\ \ lit fear Jr g T \ pr jp Jr, m ;/?Hanxaii M aria Margaret Morris K>^«SBOOK.S51^0 8 THE PHILOSOPHY f •r. S' O F Sir I s a a c Newton EXPLAINED, In Six Dialogues, O N L l G H T and C O L O U R S, .« -i Between a La ; d.y and the Author. ■ -m B Y COUNT ALGAROTTI, F. R. S. F. S. A. rf* GLASGOW: Printed for R o b e r t U r i e. mdcclxv. THE CONTENTS. DIALOGUE I. I NTR 0 DUCT 10 N; a general idea of phyftcs, and an explication of the mojl remarkable hypothefes concerning Light and Colours, page 18 DIALOGUE II. That qualities , fuch as Light, Colours, and the like, ar e not really in bodies. Metaphyfical doubts concerning our fenfations of them. Explication of the general principles of Optics, 57 DIALOGUE III. Several particulars relating to Vifion, difcoveries in Optics, and a confutation of the Cartelian fyftem, 97 DIALOGUE IV. Encomium on experimental philofophy, and an expofition of the Newtonian fyjlem of Optics, 1 42 DIALOGUE V. Expofition of the Newtonian philofophy continued. 187 dialogue VI. Expofition of the Newtonian univerfal principle of attraction, \ and application of this principle to Optics, 223 Hi T O Monf! deFoNTENELLE. I F you addrelled your ingenious and entertaining Dialogues to the illu- ftrious Dead, who had firft given you the idea of that work, and therefor thought yourfelf obliged to feek your Hero even in the obfcurity of the tomb ; how much greater reafon have I to de- dicate thefe difcourfes to one of the moft illuftrious among the Living, whom I am indebted to for the exam- ple which fet me upon compofing them, and who has given me fo perfe<51 a mo- del of polite wit and agreeable writ- ing? Your Plurality of Worlds firft fof- tened the favage nature of philofophy* and called it from the folitary clofets and libraries of the learned, to intro- duce it into the circles and toilets of A V ladies. You firft interpreted to the moft amiable part of the univerfe thofe hieroglyphics, which were at firft only for initiates; and found a happy me- thod to imbellifh and interfperfe with ' moft beautiful flowers a field, which once feemed incapable of producing any thing but the moft rugged thorns and perplexing difficulties. You may be faid to have committed the care of j revolving the heavens to Venus, and the Graces, inftead of thofe intelligen- ces to whom ignorance had anciently affigned that office. The fuccefs was anfwerable to the beauty and novelty of the undertaking. That half of our world, which always commands the votes of the other, has given its approbation to your book, and in the moft agreeable manner con- fecrated it to pofterity. May I venture to flatter myfelf, that my Light and Colours will have the fame fate as your Worlds? If a de- fire of pleating thofe who afford us fo V much pleafure, were fufficientto make its fortune, I fhould have nothing to envy you. But I am too fenfible of the very many defeats that attend my per- formance, defedts that I cannot help lamenting-, for not to fay any thing of your talents, and that happy art of rendering every thing you undertake entertaining and agreeable, the plura- lity of Worlds, which you have chofen for your fubjedt, feems of all others to prefent the mod pleafing and elegant images, and is therefor the mod agree- able to your dialogids, that the vaft field of philofophy could ever fupply you with. It prefents to the mind no- thing lefs than the liars and planets, the nobleft and mod fhining objedts of the univerfe. There are but few of the fubtile enquiries of fcience, into which you are obliged to enter. The arguments, upon which your opinion is founded, do not carry fuch a cer- tainty in them, as- to make the conver- fation grow lan quid. A 2 \ vi I have endeavoured to fet truth, ac- companied with all that is neceffary to demonstrate it, in a pleafing light, and to render it agreeable to that fex, which had rather perceive than under- hand. Light and Colours are the fub- jedt of my dialogues; a fubjedf, which, however lively and agreeable it may feem, is not in itfelf either fo pleafing or fo extenfive as your worlds. I am obliged to defcend to many difficult and minute particulars of knowlege ; and my arguments are unhappily inconteftible experiments, which muff: be explained with the greatefl: ac- curacy imaginable. It was indeed juft, that the ladies, who by your work had been made acquainted with the great change introduced by Des Cartes into the thinking world, Should not be ig- norant of the new, and, it is probable, the laft change, of which the iliuftri- ous Sir Ifaac Newton was the author. But it was extremely difficult to reci- vilize this favage philofophy, which Vll in the paths of calculation and the moft abftrufe Geometry was returning more than ever to its ancient aufterity. You have embellifhed the Cartefian philo- fophy; and I have endeavoured to fof- ten the Newtonian, and render its very feverities agreeable. However, the abftrufe points, upon which I have been obliged to treat, were only fuch as are abfolutely necef- fary, and always interfperfed with foraething tharmay relieve the mind from that attention which they require. In the moft delightful walk we are fometimes glad to find a verdant turf to repofe ourfelves upon. Lines and mathematical figures are entirely ex- cluded, as they would have given thefc difcourfes too fcientific an air, and ap- peared formidable to thofe, who to be inftrufited muft be pleafed. Mathema- tical terms are as much as poftible a- voided; and if ever any do occur, thev are explained by the afiiftance of the moft f amiliar objects. The difficulties A 3 VUL raifed againft any particular experi- ment, the hiftory of optical inventions, metaphyfical doubts, and the various opinions of different philofophers, pre- ferve the fubje<5t from that continued uniformity, which would make it dif- agreeable and tedious. I have endea- voured as much as poffible to render it lively, and make my readers intereft themfelves in it as they would in a compofition for the theatre. Is there any thing, efpecially where ladies are concerned, in which a writer fhould omit any endeavours to move the heart ? The marvellous, of which the heart, always defirous of being affetSled, is fo fond, happily arifes in true philofophy of itfelf, without the help of machines. I have made a fort of change or ca- taftrophe in the philofophy of my Mar- chionefs, who is at firft a Cartefian, af- terwards a profelyte to Malebranche, and at laft obliged to embrace the fy- ftem of that perfon* who ought to be IX placed at the head of his fpecies, if fu- periority and rank among mankind were determined by ftrength of genius and the moft comprehenfive know- lege. This great philofopher’s general fyftem of attraction is not omitted, be- caufe it has a natural connexion with the particular attraction obferved be- twixt bodies and light. Thus thefe dialogues may be confidered as a com- plete treatife of the Newtonian philo- fophy. The fanCtuary of the temple will ah^pys be referved for the priefts and favourites of the Deity; but the entrance and its otherlefs retired parts will be open to the profane. The ftile I have endeavoured to fol- low is what I believed moft proper for dialogue, clear, concife, interrupted, or interfperfed with images or turns of wit. I have taken the utmoft care to avoid thofe perplexed and long periods clofed by the verb, which only ferve to run the reader out of breath, and are befide repugnant to goodfenfe, and X much lefs agreeable to the genius of our language than is generally believ- ed, and certainly cannot be agreeable to the genius of thofe, who write with an intention of being underftood. I have left them entirely to thofe, who forfake the*Saggiatore for the'j'Fiam- metta, together with thofe antique and obfolete words which conftitute fo great a part both of their knowlege and de* light. The Count di Caftiglione, in his Courtier, two centuries ago, ventur- ed to write in fuch a manner, as to be underftood by his contemporaries, and throwing afide the affetftation of Gothic terms, adapted his manner of writing to the forms of fpeech in ufe among the polite and well-bred perfons of his time. Cuftom the fovereign judge in all languages, except perhaps our own, was his guide ; and Trus he en- riches us with the fineft piece, as far * An Fpiftle from Galileo to Virginius Csfariims, in -which the au- thor gives a very elegant expofition of his fyftem of Phyfics and A- ftronomy t A Romance, by Bcccace. xi as regards the ftyle, which the Italian language has to boaft of. For what reafon fhould I think myfelf obliged to make ufe of the antiquated difcourf- es of fome clamorous haranguer of four hundred years Handing, as a mo- del for a work of philofophy and po- litenefs ; and rather than talk to ladies in the language of the prefent age, addrefs my difcourfe to the devotees of the thirteenth century ? This minute difiertation I thought in fome meafure due to yourfelf, to let you fee how little I have negledled in a manner of writing, which may be regarded as your own. Nor was it lefs due to my countrymen, lince this work, whatever it be, is written in their original language. Young ma- thematicians, in giving the folution of a problem, generally defcribe the &eps by which they investigated it: it is only thofe of an eftablifhed reputa- tion who are permitted to give the fim- ple folution, and leave to others the Xll care of finding by what means they attained it. I would not however appear to fet a greater value upon this work than perhaps the world will think it de- fences, or fuppofe myfelf to have given a perfect folution of this problem. I am too well acquainted both with my- felf, and the difficulty of the enterprize, to entertain lo high an opinion of the performance. I have perhaps only fe'en the method, which ought to be followed, and yet have not followed it myfelf. Raphael ^nd Guercino had nearly an equal knowlege of the pre- parations neceffary for the right de- figning of a figure, and yet were ex- tremely unequal in the execution of it. Whatever may be the fuccefs of my undertaking, the ladies, for whom this work is principally intended, ought at leaf: to think themfelves obliged to me, if I have procured to them a new kind of amufement, which others may per- haps carry to a greater degree of per- fection; and if I have brought into xiii Italy a new mode of cultivating the' mind, rather than the prefent momen- tary faffion of adjusting their head- drefs and placing their curls. Travellers fliould be the importers of wit, and of thofe reciprocal advantages, which dif- ferent nations even in this refpecft have over each other. Happy the fociety formed upon the Italian fancy, the French politenefs, and Britifh good fenfe! We ought to think ourfelves obli- ged to your nation, and yourfelf in particular, for giving us an example to render common and eafy what was once myfterious and difficult, and to write in our own language what by a fuperftitious veneration was appropri- ated to the Latin, and at the fame time perplexed with Greek, that mod for- midable weapon of pedantry. We may in this refpe<5t call the fame reproach on the Italians as Mr. Pope does in a- nother cafe on the Engliffi in his fine prologue to Cato. Our fcene precarioujly fubjljls too long On French tranjlation and Italian fong . xiv Dare to have fenfe yourf elves, aftert the ft age. Be jiiftly warm'd with your own native rage. If we except fome tranflations from the French, there is nothing among us but fongs and cohesions of verfes, which every day overfpread us like a deluge, and are the torments of our age. In the modern books, written in the Italian language, the ladies can find nothing but fonnets full of a me- taphyflcal love, which I fuppofe muft affedt them as little as the antiquated expreflions of fuperannuated Cicifbei. Let the age of realities once more arife among us, and knowlege inftead of giving a rude and favage turn to the mind, and exciting endlefs difputesand wrangling upon fome obfolete phrafe, ferve to polifh and adorn fociety. I have at leaft opened the way to fome- thing, which is neither grammar nor fonnet ; and I fhall flatter myfelf to have done much more, if what the ladies infpired me with, has the good for- tune to meet with your approbation. DIALOGUES 0 N LIGHT and COLOURS. DIALOGUE I. A general idea ofPbyfics, and an explanation of the mojl remarkable hypothefes concerning Light and Colours. T HE very fame reafon that led me every day to a concert of mufic, a gay and elegant entertain- ment, a ball or the theatre, induced me to write an account of the manner in which I paffed my time laft fum- mer in the country with the marchionefs of E , and has thus, from an idle and ufelefs member of fociety, rendered me an author. And the natural defire that every author has to appear in print (whatever thefe gentlemen may tell us in their long prefaces) engages me at prefent to publifn this account. It is entirely philofophical, and compofed of certain difeourfes which I had with that polite lady on the fubject of Light and Colours. Some will, I make no doubt, condemn me for having paffed my time lo ill with a lady ; and indeed I have condemned myfelf for it. But if they knew what an engaging manner the marchionefs has of obliging every one to what fhe defires, I am per- fuaded they would forgive me, even if I had read her Guicciardini’s * hiftory of the wars of Pifa, if fhe could have defired it. But however inexcufable my error might be, I conftantly endeavoured to amend it, whenever I could * An Italian hiftorian very prolix and tedious. It was a laying of Dr. Donne’s, that if Mofcs had wrote like Guicciardini, the whole world would not have been big enough to contain the hiftory of its own creation. B i8 dialogue I. difengage myfelf a little from Light and Colours: and indeed both the beauty of the marchionefs, and the nature of the place, which feemed formed to fupport what fhe had everywhere given birth to, infpired a difcourfe quite different from that of philofophy. The little peninfula of Sirmione, the country of the polite Catullus, and thofe mountains which have fo often repeated the fine verfes of Fracaftorius *, two remarkable points, if I may ufe the expredion, in the poetical geography, formed a didant profpc£t to a fine feat, placed on an eafy afcent, that was watered below with the clear dreams of the Benaco f , which by its great extent, and the roring of its waves, feems to rival the ocean. The orange trees that diffufed their odours along the banks, and perfumed the air all around with a delightful fragrance, the coolnefs of the woods, the murmur of fountains, the veflels that fpread their fails along the chrydal lake, each of thefe agreeable obje&s would have alternately ravifhed my fenfes, if the goddefs of this delightful place had not wholly engaged my attention. To the charms of wit, and the mod polite imagination fhe joined an uncommon drength of judgment, and to the mod refined fentiments a learned curiofity. Superior to the red of her fex, without being folicitous to appear fo> * Jerom Fracaftorius was born of a noble family at Verona in Italy, about the year 1483. He ftiulied plvyfic, until a few years before his death, when he devoted himfelf entirely to the ftudy of polite learning, mathematics, aftrenomy, and cofmography. He died of an apoplexy in 1553, and was interred in the church of St Euphe- mia at Verona, where in 1559, he had a ftatue eredfed to him by or- der of that city. His poetical works are much admired, the princi- pal of which are his Syphilis ; Jofcph an epic poem in two books, but left unfiniflred at bis death; and his Alcoa, feu dc cur a canum venati- corum. See his life prefixed to his works ; foam. Imperial! s , rnuficum hiftoricinn. pag 16. Les dopes dcs homines favons , tirez del hijiorie dc JSI. dd Thou. Tom. i. pag. 189. 4 A lake in in the territories of Venice, now called Lagodi Garda ■ On Light and Colours. 19 ihe could talk of ornament and drefs whenever there was occafion for it, and alk proper queflions upon more im- portant fubjedls. A natural negligence, an eafy unaffec- tednefs, embellilhed all fhe faid. She had beauty enough to gain her confort many friends, and judicious enough not to (hew any one a particular regard ; and thele ac- complifhments being feldom found united except in books and the imagination of authors, is the reafon, I believe, that learning in ladies does not meet with fo univerfal an applaufe from the world as their beauty. When impertinent vifitors gave us fome refpite from play, that relief and plague of fociety, we palled fome part of the day [in reading ancient and modern authors, contrary to the opinion of that monarch * who preferred old books like old friends. Our principal reading was poetry, as this feemed of all others moll; agreeable to the country from whence the genealogies of polite literature tell us it derived its original. But, however, that we might preferve a certain fpirit of liberty, upon which all our converfation was grounded, we did not entirely ex- clude that fort of poetry which is formed exprefly for the town, as fatire, comedy, and epic. This fpirit had a more particular influence upon our criticifm, which re- garded an Italian, a French, an ancient and a modern author, with an equal impartiality. The fober dignity and purity of the Eneid, the variety and perfpicuity of Oi lando f uriofo, the noble finilhing of the Gierufalemme Liberata, the juftnefs, the philofophical fpirit, and the * Alphonfus the rothkingof Arragon, firnamed the Wife, who ufed to fay, he defired little more than four old things, viz. old wood to burn, old Wme to drink, old books to read, and old friends to live with. He began his reign in 12.52,, and died in 1284, B 2 --0 D I A L O G U E I. peculiar beauties of the Henriade, the invention of the Mandragora *, the characters of the xMifanthrope, the fweetnefs of verfe in f Sannazarius, and the happy negli- gence of Chappelle ; all thefe we compared in fuch a man- ner, that we neither efteemed a verfe the more harmoni- ous for its antiquity, nor a thought lefs fublime or ele- gant from any difference of country. We interfperfed our difcourfe with epifodes and digreflions, which the marchionefs did not think herfelf lefs obliged to me for, than if I had given her an encomiurcrupon her beauty. In one of thefe digreflions, I fpoke of the force and ad- vantages of Englifh poetry, which gave her a ftrong in- clination to be acquainted with it, 'imagining that a nation, to whom Minerva had laviihed her favours in fo profufe a manner, could not be deftitute of thofe of Apollo. As I defired nothing more than to give pleafure to a perfon who continually afforded fo much to me, I was extremely forry that I could trace her only a very low and imperfeift idea of Dryden’s harmonious copioufnefs. Wal- ler’s foftnefs. Prior’s various and eafy ftile, the lively wit and fire of Rochefter and Dorfet, the corned majefty of Addifon, the ftrong and manly ftrokes of Shakefpeare, * Mandragora or Mandragola, an Italian comedy written by the famous Nicolas Machiavel. f ACtius Sincerus Sannazarius was born at Naples of a noble fa- mily in 1488. He was fecretary to Ferdinand king of Naples, who honoured him with a great fhare of his confidence and efleem. He was eminent for his Italian and Latin verfes. He fpent twenty years in correcting and polillring his poem De Partu Virginis ; but his pifcatory Eclogues in Latin, which he wrote when he was young, were preferred to all his other poetical writings. He was rewarded by the Venetians with a prefent of 600 crowns for his celebrated epigram, Viderat Hndriacis Venetam, etc. He died in 1J30 of grief, becaufe the prince of Orange, who was general of the imperial army, had demolifhed a tower belonging to his country-houfe. He lies interred near Virgil’s tomb. See Pnu- ks Jovitis in Elogiis, etc. 21 On Light and Colours. and the aftonilhing fublimity of Milton. To fpeak of the merit of a poet, is the fame thing as endeavouring to de- fcribe the beauty of a face, which can be judged of only by the fight ; and to quote, even in its original language, only one particular pafi’age feparate from the reft, would be the fame as fhewing an eye, a lip, or a dimple of a face, of which we defire to fee not fingle features, but the whole, whofe beauty and fymmetry are the refult of innumerable charms. However it gave me a little confo- lation when I remembered, that, among fome papers which I happened to bring with me into the country, I had Mr. Pope’s Ode on St. Cecilia's day. None can be unacquainted with the name of this great author, with- out at the fame time ignorant that there is any fuch thing as poetry in the EngUJh language. The next morning I carried this fine Ode with me into the grove dedicated to our poetical converfation, and now become the Parnafius of all nations. After having begged pardon of the Eng- HJh mufes, I tranflated it as well as I could, and began to read. The marchionefs liftened to me with an attention that fine ladies feluom give themfelves the trouble of. When 1 came to this pafi'age — — While in more lengthen'd notes and flonn * The deep majejlic foleinn organs blow ; Ihe interrupted me, and could not enough admire the propriety of thefe epithets, which, added fhe, defcribe that inftrument in fuch a manner that I really hear it play. 1 cannot tell whether you hear it too, but I think I may reafonably conclude it from a certain pleafure you fhewed, perhaps, infenfibly, in reading this pafi'age to me. You * Mentre con tarde ed allungate note II profundo, l'olenne, e maeftofo Organo foffia B 3 22 DIALOGUE!, are fo well acquainted. Madam, with the molt fecret mo- tions of my heart, that it is impodible for you to be de- ceived ; and you commend a thing that certainly renders the image, which is the fupport of poetry, extremely lively and expreffive. Thefe forts of epithets are the ftrokes that give life to the picture. A white hand, a ferene brow, and bright eyes, are at bed but the rough draught of it. Now we are fpeaking of epithets, is not the feven-fold Light, which I read of fome time ago, replied the mar- -chionefs, in an Ode made in honour of the philofophical lady * of Bologna, fome Chinefe hieroglyphic ? at lead it is fo to me and many others whom I have defired to ex- plain it. You mean, anfwered I, • The fevenfold Light IVhence ev ry pleajing charm of colour fprings, And for?ns the gay variety of things f . If you knew the force of this epithet, you would fee ;i Newtonian picture in dead of a Chinefe hiereglyphic, though perhaps a little too philofophical for poetry. What ! anfwered fhe, interrupting me with an air of furprize, you underhand this paflage as well, as if it was the pro- duction of an Englilh author. I am of opinion, Madam, anfwered I, that the verfes of an Italian who has the ho- nour to be a great admirer of you, are infinitely preferable to thofe of an unfortunate Briton, who has the unhappi- nefs of being at fo great a didance from you. I under- hand you, continued fhe, and I need not defire a better * Laura Maria Kalherina Barfi, a learned lady in Italy, who iu at 19 years old, held a philofophical deputation at Bologna, upon’ which fhe was admitted to the degree of dottor in that tmi- veihty. •{• Odell, aurata Luce f'ettemplice I varioardenti, e midi almi color!. On Light and Colours. 23 encomiaft than you, if it be true, that no one underftands the fenfe of an author fo well as himfelf. Come then, fince you are the author of this piece, deliver me from the perplexity I am under about this fevenfold Light, and the reft of your Newtonian picture, which gives me great rea- fon to believe, that in praifing one lady, you have ufed your utmoft endeavours that no other fhould underftand, your meaning. It is certainly that profound refpefl that I have for you. Madam, anfwered I, which has made you find me out. Afterwards, reflecting that it was im- poffible to give her in few words an explication of Sir Ifaac Newton’s optics to which thefe verfes allude, a thing which fhe had not the leaft idea of, had not we better follow the example of the theatre, Madam, faid I, where the play is generally at an end when the perfons come to a knowlege of one another ? And befides. We fhould finilh Mr. Pope’s Ode, which will certainly give you a far greater pleafure, than any comment upon mine. No, no, faid fhe, we will finilh that another time, and for the prefent we fhall a cl contrary to the theatre, but without forgetting the cataftrophe, or finding myfelf i n as much ignorance as ever. Being willing to give her fome idea of the fyftem to which thefe verfes refer, and thinking that the Marchio- nefs would for once be like other ladies, who are often defirous of feeming to underftand what they are not fup- # pofed to have the leaft notion of, I told her as briefly as I could, that according to Sir Ifaac Newton’s opinion, or rather as the thing really is, every ray of light is compofed of in infinite number of other rays, fome of which are red, fome orange and yellow colour, others green, fome blue, fome indigo, and others violet ; and that from thecompoli-' tion of thefe feven colours in a direct ray from the fun arifes the 24 DIALOGUE I. white or rather golden colour of light: that if this di- rect ray from the fun is refradted by a certain glafs called a prifm, thefe rays of which it is compofed, differing in colour, differ alfo in degrees of refrangibility. 1 fee, faid the marchionefs, interrupting me in a manner very different from what I expedted, that your^comment has more need of an explanation than perhaps the text itfelf. But this is my fault in not being able to underhand your refraction , different degrees of refrangibility , and the like, which quite confound the idea I had begun to form. But pray explain yourfelf in fuch a manner that I may not have any farther reafon to accufe you with obfcurity, nor my own dulnefs with being the caufe of it. You will not be 1'atisfied, anfwered I, unlefs I make you a comment at lead as long as that of the Malmantile, which, I obferved to you the other day, feemed to be didfated by the agreeable Mathanafius # who was former- ly the Moliere of the commentators: at leaf!:, laid fhe, Newton will enter more properly here than Micheli does there, whofe difcoveries are of no fort of fervice to illuftrate this poem ; and fince all you faid was fpoke with an air of ferioufnefs, and fuch confidence that you did not fcruple faying, according to Sir Ifaac Newton’s opinion , or rather as the thing really is, you have made me extremely de- firous of becoming a Newtonian. This, anfwered I, is a very ready method of propagating Sir Ifaac Newton’s philofophy and bringing it into fafhon. Pemberton, Graveiand, and Dunch, the zealous propagators of this * Monfieur c’e St. Hyacinthe, under the fictitious name of Dr. Mathanafius, publifhed a piece intitlcd. Chef d'Oeuvre dim Inconnu avec des remarques, in order to ridicule the impertinence of fome cri- tics and commentators. The Malmantile is an Italian piece wrote after the manner of this author. -On Light and Colours. 25 fyhem, would be very glad to give the care of it to you. But what will Mr. Pope fay, fhewing her the book which I had ftill in my hand, if you leave him in the beginning of this fine Ode, for a fudden fancy that you have taken to light and colours ? Mr. Pope, anfwered fhe, cannot be offended at my leaving him for a philofopher, and fuch a philofopher as Sir Ifaac Newton, one of his own country- men too. Do not you know, faid I fmiling, that the poets look upon themfelves as facred, and when they have once got this enthufiafm into their heads, they regard neither country nor relations, but think themfelves greater than any philofopher, even if he had difcovered wherein confifts the union of the foul and body ? It is well for us> laid fhe, that the poets have more modefty than to declare this in their writings. It fignified nothing for me to plead incapacity and many other excufes, which are made ufe of on the like occafions, and which occurred to me upon this. The marchionefs infifted upon feeing my Newtonian pidture as fhe called it. I beg- ged fhe would at lea ft have patience till evening, telling her that the night had always been the time confecrated to philofophical affairs ; and that the moft polite philo- fopher in France had made ufe of it in a circumftance re- fembling mine, and made no fcruple of entertaining a fine lady with philofophical difcourfes in a wood at midnight. But we, Sir, replied the marchionefs, ought to make ufe of the day, which is certainly more proper than the night for a difcourfe on light and colours. She fpoke this with an air of authority that inforced her commands in the moft amiable manner, and made it a pleafure to obey. Thus I was abfolutely obliged to begin, but the diffi- 2 6 D I A L O G U E I. culty was how to do it ; for fhe had not the leaft notion of phyfics, which it was ncceffury to give her a general idea of, before I proceeded to a difcourfe upon light and colours on the Newtonian fyftem. At laft, after having again in vain reminded her of Mr. Pope, and other fubje&s that required lefs application and afForded greater plea- fure, when the heat of the fun, which was now almoft at his meridian, obliged us to retire into the houfe, 1 began after the following manner. It is natural to fuppofe that after fociety was fo well efta- blifhed among mankind, that fome of then} had nothing to do, which I look upon as the epocha of its perfection. Thele perfons either from that curiofity, which we natu- rally have about thofe things that concern us leaft, or perhaps for fear of being charged with idlenefs by the reft, applied themfelves to conftder that variety of things of which this univerle is compofed, their differences and ef- fects. It is probable too, that one of the firft fpeculations that thefe idle people, who afterwards affumed the name of philofoph ers, employed themfelves about, was concern- ing the nature of light, which is certainly the moft beau- tiful and confpicuous objeCt of our fight, and indeed the means by which we fee every thing elfe. T his confequent- ly led them to the colours which this light depictures upon objects, and which diffufe fuch a variety and beauty on our world. Thus, t I believe, that Optics , which is that part of natural philofophy that regards light and colours, and in general all natural philofophy, had their origin among men at the fame time with their idlenefs : indeed it was of a latter date than fome parts of morality and geometry, which were abfolutely neceffary in the ear- lieft ages of the world, but contemporary to poetry, if 1 On Light and Colours. 27 you will, and antecedent to metaphyftcs, which required a ftlll greater vacation from bufinefs. I am pleafed, replied the marchionefs, that poetry and • natural philofophy have one common date ; fince for that l reafon you will not perhaps think this tranfition fo ftrange, that we have made from one to the other upon my account. The tranfition, anfwered I, that our philofophers made from a flight knowlege of things to an ambition of unfold- ing nature and penetrating its effeffs, was much ftronger. This, in the language of philofophy, is called making fyjiems. This is juft as if any one, after having had a curfory difcourfe with a fubtile minifter of ftate about good or bad weather, fhould attempt to write his charac- ter, and pretend that he had penetrated his moft profound decrets They fhould have begun with a very attentive examination of< things, drawn from frequent obfervations and diligent experiments before they ventured upon the leaft fyftem They were to aft, if poffible, like thofe two antient philofophers ; one * of whom, in order to write on the nature of bees, retired into a wood, that he might have the better opportunity of confidering them ; and the other f fpent fixty years in making obfervations upon thefe infefts. But the misfortune is, that experiments and ob- fervation require patience and time, and very often we are indebted to mere chance for the muft ufeful and entertain- ing among them. On the other hand, men are always in hafte to arrive at knowlege, or at leaft to have the appear- ance of it. After this, the revolutions of ftates, the rude and unculti- vated manners of the people, the temper of nations, and * Philifcus. Vid. Plin N. H. L. xi. C. 9. f Ariftomachus. Id. ibid. 28 DIALOGUE I. the profeffion of thofe, among whom philofophy had for- merly flourifhed, did not a little retard its progrefs. From the Indians traditions which their priefts kept to themfelves with as much jealoufy as they did their genealogies, and from the Egyptian temples, where it had long lain hid under myderies and hieroglyphics, philofophy at length took its feat in the portico’s and gardens of Greece, where it was very foon embellifhed, and corrupted with al- legory, fables, and all the ornaments of eloquence. Ima- gination, which is the charadteridic of the Grecian genius, prevented philofophy from taking any deep root, and in- deed it was attempted to have been totally extirpated by the eloquence of a man, whofe difcourfeswerediftinguilhed a certain grave and elegant pleafantry, which made him mailer of the moll powerful arts of perfuafion, and who had been judged by the oracle the wifeft among mor- tals. He averted, that we have nothing to do with what is above us, and drove to reclaim our curiofity and du- dies from natural to moral objedts ; from the combinations of the univerfe, to the little chaos of human extravagan- cies, and from that rapture with which we are tianfport- ed by the contemplation of vaft and diftant objefts, to the melancholy confideration of our own emptinefs. And this perfon, who, more dedrudtive than Pandora, engaged mankind in a confideration of that train of evils which had ilfued from her fatal box, without giving them * any hopes of a cure, was had in the highefi veneration, as the father of a new philofophy called moral, which is of all others the mod treated of and the lead underdood. * It is probable that the greater part of thofe, who are acquaint- ed with the charaaer of Socrates, will think our noble audio palled too fevere a cenfure. On Li G itt and Colours. 27 Philofophy after this, together with luxury, riches, and corruption, was tranfported from Afia to Rome. It could make but little progrefs among a people who cultivated hardly any other arts but thofe of pardoning the vanquilh- ed, and depreffing the proud. In the firft ages of chri- ftianity, philofophy lent its affiftance to combat paganifm, and after .this was fubdued, it raifed fo many civil wars and dilfentions among thofe who by its affiftance had tri- umphed over Jupiter and Olympus, that the ecclefiaftical Ihip feemed in danger of perilhing when it was hardly loofed from the port. To this fatal war of words fuc- ceeded that which the Barbarians raifed againft learning and the Roman empire, wherein both were equal fuffer- ers; for it deftroyed the one, and funk the other, untill from the profound darknefs, which afterwards followed, fome fparks of antient knowlege were re-kindled among the Arabians. The dottrine of Ariftotle revived, and be- ing fpread through the Raft, was gladly embraced by the monks, as it was the moll fuitable to their manner of life. How much pains and lludy are neceffary to frame a right philofophy ! It requires no lefs art and labour, than to make thofe fine filks which you ladies are adorned with. But the philofophy, in which the name of Ariftotle fup. plied the place of reafon, did not greatly difturb the mo- nadic tranquillity. This philofopher.who was banifhed * from Athens by the antient priefts, was, but with fome * Ariftotle retired from Athens, in order to avoid aprocefs ofir- Teligion which the Athenian priefts carried on againft him. The circumftances of this affair are unknown : fome affert, that he was charged with impiety on account of a hymn which he had made in honour of his friend Hermius. This hymn is ftill extant, but there is not the leaft impiety difcoverable in it ; but his accufers urged that he had prophaned divine fongs by proftituting them to the ho- nour of a mortal man. Ariftotle, not thinking it fate to truft to the interpretation this little. poem might meet with, retired verv pri- C 28 DIALOGUE r. variety of fortune, received by ours; who, though they once condemned him as a* pernicious author, yet after- wards carried the zeal for him to fuch a height, as to be- 1 lieve him not ignorant even of thofe things which are a-t bove the reach of human reafon. Religion at this time was more than ever united with philofophy, which could not fail to produce the utmoft confufion in the one, and] ignorance in the other, fince both their nature and end are extremely different, A chaos of vain and ufelefs difputes, a chain of unin- telligible definitions, a blind zeal for wrangling, and a ftilJ blinder devotion for Ariftotle whom they called, by way of vately to Chains, where he pleaded his caufe at a diftance by writ- ing, which was the fafeft way lie could take: for his accufers were a let of men who would never have let him been at reft. Others af- firm that he was driven from Athens for the goodnefs of his morals. Some authors report, that this philofopher drowned himfelf in the Euripus, a narrow fea near Eubsea, becaufe he could not find out the reafon of its ebbing and flowing feven times a day. But themore; received opinion is, that his very great application, in the ftudy of' this phenomenon, brought an illnefs upon him, which occafionc-d his death. See Bayle’s life of Ariftotle in the general dictionary,' vol. II. * The French, who took Conftantinople about the 13th century,,, having brought the books of Ariftotle into their own country, his doCtrine began to be publickly taught in the univerfity of Paris, and continued fo for fome time. But Arnaury a ftudent of that univer-j: fity, having advanced feveral obnoxious opinions, and endeavoured to defend them from the principles of Ariftotle, the phylics and metaphyfics of that philofopher were burnt by order of a council 1 held at Paris in 1109, and the reading of them prohibited under pain of excommunication. This prohibition was confirmed about the year iiij, by the Pope’s legate, who was employed to reform the univerfity of Paris; but lie allowed the logic of Ariftotle to be taught. Gregory VII. renewed this prohibition in 1131, but with tills addition, that he only forbid the reading of Ariftotie’s works till they fliould be corrected. In ntfi, Simon the legate of the fee j of Rome in his reformation of the univerfity confirmed the regula- tion of the year 1x1 j, relating to Ariftotie’s writings without men- tioning the correction of them. But in the reformation of the uni- verfity in 1366, this philofopher’s phyfics, as his other works, were allowed to be read. Vid. Father Rapin’s companion of Plato and : Ariftotle; Du Pin’s Nouvelie bibl. etc. Light and Colours. 26 ••j Jiftindtion , the pkilofopher , or a fecond nature, and above all a ;ertain jargon of indeterminate, oblcure and hard exprefii ■ hj ms, either without any meaning, or confufed, overfpread, ike a deftroying deluge, the face of the whole earth, and tor many ages ufurped the pompous name of fcience. As j iamong the Chinele he is efteemed the moll learned, who can read and write more words and figures than the reft, ajfo he was counted to have mod learning amongft us, who, in a particular habit, could pronounce in certain places, and with certain geftures, and feemed to uuderftand the : greater number of expreffions in this vain and pedantic jargon^ The diftinctions and anfwers might be as eafily forefeen by any one who had a little examined their me- moirs, as the turns of muftc in country fcrapers, or the jingling of rhyme in bad poets. Such were the vails under 1 which they hid, from the eyes of the world, that ignor- ance which very often they could not hide from themfelves. The pride of fchools was fupported by the noife of empty words, and the tyranny of names. It was imagined that they really contended for truth, but thefe gray headed children in reality amufed themfelves only in fighting with bubbles. This obftinate veneration for the antients, which for a long while palled among the philofophers as hereditary from one generation to another, was the caufe that the knowlege of phyfics made little or no progrefs till the laft age. At length, among fome few others, who were to fall as it were martyrs to reafon, there appeared in Tufi- cany a perfon named * Galileo, who had the courage not * Galileo was born at Florence in 1564. He was put into the inquilition for maintaining the diurnal motion of the earth, and averting the fun and not the earth to be the center of the world. Thefe propofitions were condemned by the Inquilitors as falfe and heretical. He was not difeharged till he had promifed to renounce C 2 30 DIALOGUE I. not only to fay, but what is worfe, to demonftrate wit] the cleared evidence, that men, who had perhaps for fixt; years been honoured with the title of doctors, or fat in th< chair of philofophy, had taken very great pains all theii life long to know nothing. All this boldnefs coft hirr dear ; for to venture to make ufe of his reafon was the fame thing as reproaching them with the general abufe they had made of theirs ; and to endeavour at the promo- tion of knowlege was as dangerous as an attempt to change the boundaries of antient Rome, which the Augurs took fueh a religious care in the prefervation of. After fuch a courfe of ages, he fhewed them what ought to have been done at firft, and began to make a fearch into nature by obfervations and experiments, reducing himfelf to that ignorance which is ufeful for arriving to fome knowlege at lafr. - [ I think it not improper to call this man the czar, Peter I the Great, in natural philofophy : each of them had to do with a nation pretty near the fame charafter. No one people ever ufed fuch endeavours for knowlege, as the Mufcovites did to know nothing. They forbid all ftrang- ers to come into their country, and all the natives to go out of it, for fear they fhould introduce fomething new. ^■Tr-niua*, ,| his opinions, and not to defend them either by word or writing, or j infmuate them into the mind of any perfon. Upon his publilhing his dialogues upon the two chief fyftems of the world, the Coper- nican and Ptolemaic in 1631. he was again cited before the holy office. The fame year the congregation convened, and in his pre- fence pronounced fentence againft him and his book, committing him to the prifon of the holy office during pleafure, andcommanding him as a having penance for three years to come and repeat once a week the feven penitential pfalms, but referving to themfelves the power of moderating, changing, and taking away, altogether or in part, the above mentioned punifhment and penance. He was dii- charged from his confinement, in 1634, but the impreflion oi his dialogues of the fyftem of the world was burnt at Rome. Vid. the general diiftionary. On Light and Colours. 3* “Thus was it with thefe philofophers, who, jealous of their 'tenets, renounced every experiment, and more certain de- J: monftration of the moderns, rather than introduce any ;i: novelty or reformation into their ownfyftems: but as force 1 has generally more influence upon 'men than reafon, the :: Czar compaffed his defigns fooner than Galileo, who was at the fame time obftrudted by another fpecies of philofo- phers, who were by fo much the more formidable as they too defpifed the antients, which now began to be the falhion, and aflerted things in oppofition to them of which every one had a clear and diftindt idea. They introduced exadtnefs and order in wTiting, which were then as un- common as they are natural and neceffary, and by means alone of certain motions and figures, which they knew how to give to bodies at proper times and on proper occa- fions, promifed to unfold what feemed the mold unexpli- cable in nature. You may eafily imagine that the mag- nificent promifes of thefe philofophers, which fo agreeably flattered the ambition of the human mind, which Galileo’s obfervations ferved rather to humble, joined to a certain fimplicity that gave fuch an sir of wonder to their fyflems, as it does to a well concerted romance, mu ft naturally fe- duce many people, and form a feet. And it indeed had this effedt ; fo that thefe moderns too began to have expo- fitors, and followers as obftinate and zealous as thofe of the antients had been before ; and thefe made themfelves the more ridiculous by laughing at the fame fault in others. But it was a melancholy thing to fee an experiment fome- times offer itfelf, which had never before been known or thought on; and the fineft and moft artificial fy Items, which had perhaps coft their inventors whole months of labour and ftudy, fhamefully fall to the ground, c 3 32 DIALOGUE I. In order then to avoid thefe forrowful reflexions, fait! ' the marchionefs, it is neceffary for thofe, who would form ! a fyftem in any thing, to be careful firft to take notice oi all that is obfervable in it, that it may not be expofed to the mercy and infults of experiments. This is exaXly whati the Newtonians fay, anfwered I ; and certainly, madam , [ you muft have fome fecret intelligence with them to be fo well informed of their fentiments. It would be ridiculous for a mechanic to take it in his head, to guefs how the fa- mous clock of Stralbourg is made within fide, if he had not firft acquainted himfelf with the outfide, the manner in which it ftrikes, and thofe many other things it does be- fides telling the hour. Thus, fay they, if we can ever I hope to make fyftems that carry fome appearance of being durable, it will be then only when by the means of experi- ments and obfervations we lhall know all, that in terms of art is called phenomenon, which fignifies the appearance of things, and the laws which refultfrom thefe phtenomena, and by which nature conflanlly performs all her operati- ons. How then could Des Cartes, for example, who was the chief author of this cnterprifing feX of philofophers, make a rational fyftem concerning light and colours, when he was entirely ignorant of fo many of their qualities, which Sir Ifaac Newton afterwards difcovered by obferva- tions ? How could he form the ftatue, when he had not the marble ? This is the manner in which the reft of the philofophers of our time, and thofe learned focieties, found- ! ed and maintained by the liberality of princes, or the ge- nius of nations, proceed : they make obfervations and pre- pare materials for pofterity to build fyftems upon, more fortunate in their duration, than thofe that preceded the prefent age, This profeffion indeed is not fo pompous as On Light and Colours. 33 kjihat of thofe who will build you a world in a twinkling of njin eye ; but on the other hand it has this advantage, that . 0; t is able to make good its promifes, which is as great an ill obligation upon a philofopher, as a miftrefs. rial ■ I, who am a woman, replied the Marchionefs, confefs :.: E] that I love thofe who have the courage to venture upon ■ fo ! grand and difficult enterprifes. Is not this the reafon why ms we intereft ourfelvesfo much in the adventures of heroes ? The courage of thofe philofophical heroes has fomething i fublime and fuperior in it : if they do not attain to all they promife, mull there not be given fome indulgence to the imperfections of human nature ? On the other hand, if, as you fay, there cannot be any good fyftems, till all the phenomena are fully known, when fhall we have them ? They will happen as feldom with us, as the fecular games anciently among the Romans : and I cannot flatter myfelf that I fhall live long enough to fee fo much as one in my time. ^ I mult be contented then with thofe fyftems that we have, be they what they will. I believe. Madam, an- fwered I, that no one could have more fpecious reafons to allege in favour of trifles. I fhould ferve you right, if I put you on proving thefe reafons; but as I will ad more mercifully with you, than yom perhaps would with regard to me, fince you have a mind that we fhould reafon away that time, which might be better employed on pleafure, I will not make ufe of that right which thefe reafons of yours give me, to propofe to you ferioufly the important queftions, whether light be a fubftance, or an accident, or an ad of the pellucid, as far as it is pellucid ? Whether colours are the firlt configurations of matter, or a certain little flame that arifes from bodies, whofe parts are pro- portioned to our fight ? I might gravely alk you too, that you may fee how many things I fpare you the trouble of h dialogue r. confidering at once, whether light, or its fpirit, be the foul that Plato places between nature and ideas, to con- ned the fenfible and intellectual world? and whether it was for this reafon that Plato reprefented the element of fire, which is the feat of light, under the figure of a py“ ramid, which in fome meafure agrees with that fublime and myftic triangle which is the fymbol of the foul ? idle enigmas of the learned ignorance of pafl ages ! and who can tell but if you had fallen into other hands than mine, you might have been fet a yawning with fome gothic paf- fages out of Dante ? Or perhaps by this light, you would have been gradually conducted to divinity ; at lead you could not have got free from an explication of the myftic fenfe hid under the fable of Prometheus, who ftole light from the fun to animate his ftatue. I fee, faid the Marchionefs, that philofophers are to be dealt with in a very circumfpecl: manner, who know how to improve every thing to their own advantage. You aCt juft like tyrants, who think they confer a great favour on any one, whom they have not injured. However, I am much obliged to you, for fparing me the trouble of hear- ing all thefe fine things, which, I confefs, are quite above my underftanding. Let us fee, anfwered 1, whether you can underhand the doClrines of fome among the ancients who were more prudent and humane than the reft. Thefe laboured to explain every thing by a vacuum, and the motion and fi- gure of certain very little particles, which they called a- toms, and from thence gave their fchools the name of ato- mifts, which was perhaps the mod antient of all otherfefts, and lately tried by the fplendor of eloquence to rife upon the ruins of the Ariftotelian, in oppofition to that of Def- On Light and Colours. 35 cartes. Thefe philofophers afferted that the light of the fun, for example, was nothing but a perpetual and copi- ous ftream, of the very lfttle particles, or atoms, which, flowing from the fun himfelf, fpread themfelves every way with an incredible velocity, and fill the immenfe aerial fpace ; fo that light is always followed by new light, and one ray is as it were impelled by a fecond. You may eaft» ly underhand this by the fimilitude of a fountain. — I un- derhand it mighty well, interrupted the Marchionefs, with- out the fountain ; but I am greatly afraid that thefe ato- mihs of yours, by making' fo many particles continually proceed from the fun, will at lah turn fome fine day into midnight. Truly, anfwered I, that would be playing us a villainous trick, which no one would get any thing by, unlefs perhaps fome few beauties, who would then always be feen by candle light : but do not fear it. Revolutions of this importance require more time to be brought about, than the revolution of a monarchy. And befides, thefe a- tomifts give us fo great a fecurity that it would be a fhame to dread it. For, in the firfl place, they tell us, that the > rarity and incredible fmalnefs of thefe little particles that proceed from the fun, which fun they make to be of a denfe and clofs matter as you will fee hereafter, in a very long courfe of years will produce only a very little dimi- nution in his light. And to make you ftill more fecure, this may be confirmed by the example of a little grain of colour, which is fufEcient to tinge a very great quantity of water. An example, drawn from odorous bodies, may ferve to fhew you how very much the parts of matter may be fubtililed ; as for inftance, a grain of muffe, which, though it continually emits a prodigious quantity of parti- cles, yielding a perfume fo ftrong and quick, that at a certain 36 DIALOGUES diftance it is able to tlupify ferpents of a monftrous fizc, : and quite deprive them of motion, yet in a confiderable time its weight is but very little diminifhed. And am- ber- greafe, in the fame manner, for a long while lofes hardly any thing of its agreeable fcent. From light’s puf- fing through the denfeft bodies, fuch as diamonds, and gold when it is beaten into thin plates, we mull neceflarily infer , that the particles of light are extremely fubtile. All this is mighty well, replied the Marchionefs ; but that fuch a quantity of light fiiould continually proceed from the fun, as is fufficient to fill and illuminate the whole world, puts me into terrible apprehenfions, not- withftanding all your fine examples of mufk, amber greafe, 1 and diamonds. Have not you fome inclination, anfwered I. to the learned melancholy of the inhabitants of Dean Swift’s fly- ing illand ? who in the moll poetical allegories has given us the mod philofophical fatire upon mankind. This ifl- and, which in the language of the country is called La- puta, as it is different from all that have hitherto been dif- covered by our voyagers, fo it is inhabited by a very An- gular fpecies of men : always abltrafted and immerfed in the profoundefl fpeculations, they give themfelves up to fpleen and the mathematics, fo that they have always need of a Flapper , who, by flxikingthemfrom timetotime with a blad- der, may bring them back to the world below ; their know- lege fills them with thofe continual fears and difquietudes which the vulgar by a happy privilege of their ignorance are quite free from. They are afraid that a comet, by approaching a little too near the earth, may in an inftant reduce us to allies ; or, that the fun one day or other will fwallow us up ; or, that this immenfe fource of light and On Light and Colours. ' 37 ■’ heat will at length be exhaufted and leave us involved in a profound and eternal night. May not your fears. Madam, ' be faid a little to referable thofe of the Laputian fchool ? As to the flapper, anfwered (he, I have nothing to do with that, efpecially xvhen I am with you. But do you not think that there is fome reafon for me to be frighted at the terrible threatening of a perpetual night ? Ought you not rather to think yoarfelf obliged to me for intereft- ing myfelf fo much in the caufe of light, which you have made your heroine ? It would be quite lhameful that I fhould {hew more regard and concern for it, than your- felf. You ihall fee, Madam, anfwered I, that thefe ato- mifts have taken care to fecure your repoie, and preferve ■ Ifflts Sjiaf. aad btile. kt ceej tie what you fhew fuch a regard for. They will find you a ; method to recruit the fun with that facility -which a phi- lofopher is m after of, who knows how to make all nature :i! fubfervient to his fchemes. They will make the feeds of light and heat, which are diffufed through the univerfe, continually return back again into the fun, in order to .re* -pair his Ioffes. They will place fomething round him with which he is fuftained and reftored juft as a lamp is : fed by oil or fome other matter. We will call certain fy- 1 items to our afiiftance which will lend us comets that from time to time fhall fall into the fun and yield him frefh fup- plies : and if this be not fufficient, we will have recourfe ! to fome philofopher, who may find means to make a ftar fall into him. And if you have not confidence enough in human fyftems, we will call a celeftial one to our aid, re- vealed to Adam by an angel in Milton, who aflures us, that the fun draws his aliment from humid exhalations, and in a regular manner takes his fupper every night with the ocean. Will you have anymore? No, no, faid fhe, the 38 DIALOGUE I. one half of thefe things is fufficient to diflipate the fears of a Laputian himfelf. And I hope there will be no need at prefent to trouble any philofopher, much lefs afuperlor Being. I wilh, anfwered I, that your fears may never extend to any thing farther than philofophy, and that your beau* ty, as it has many other qualities in common with the fun, may have a common duration with him. But I am ex- tremely glad that fince I have delivered you an opinion which at firft fight gave occafion to your fear, it is capa- ble too of diffipating that fear : as you are fo very fubjedt to be frighted at every trifle, I do not know what would have happened, if I had told you the opinion of a famous antient, who affirmed the fun to be a mirror formed of a fubftance refembling the moft polilhed chryftal, that fends and refledts the light to us, which is tranfmitted to all parts of the univerfe, and there unites. What hopes fhould we have of finding proper materials above, to repolifh this mirror, if it fhould ever happen to be fullied and grow dim ? Let him, replied the Marchionefs, who made the fun a mirror, contrive how to repolifh it when it fhall want it, I had rather imagine it to be the foul of the world, and to be itfelf the fource of light. You fhould have ad- ded, that it is the fource of colours too, anfwered I, fince without light thefe entirely vanifh and are no more. Say rather, replied the Marchionefs, that they are no longer vifible. Will you tell me that an hour after fun-fet, there are no colours in this pidture ? I fhould be glad to hear you prove to me that the pidlure too is vanifhed for the fame reafon, becaufe it is no longer vifible. The pidlure, anfwered I, and the canvas ftill remain, and upon it cer- tain difpofitions in the figure and texture of thofe atoms, On Light and Colours. 39 >f which the chalks that are made ufe of m the painting tre compofed. And thefe difpofitions, at the approach of light, will again make the colours mezzotintos and ohiaro ofcuros, appear upon the canvas, and reftore to /•our fight a commanding beauty, a flight of pillars, a ver- Jant meadow, or the opening blufhes of the morning, [n the dark all thefe objects vanilh, as they are the re- fult of a combination of thofe difpofitions and light to- gether. I might allege the authority of Virgil upon this occafion, who informs us, that obje&s lofie their colours at the approach of night. Lucretius*, who, in the moft elegant verfes, has given us a body of this atomic philofo- phy, makes us apprehend moft terrible confequences from a fuppofition that bodies and their principles are endued , with colour. For, fays he, Seeds are colourlefs =, without a dye. For either this cannot to feeds agree ; Or feeds are not immortal all and free From change , and therefor things may fall to nought, Creech. You give me confequences and verfes, faid the Marchi- onefs, when I want evidence and explications. Defcartes, anfwered I, will afford you enough of this, who has dif- cufled this matter much more fully than Lucretius. His principles are different, but in this point he agrees with, the atomifts. But you want fyftems, and I muft fatisfy you : you (hall fee the moft daring proaudts of imagination, which have for fome time deceived thofe, who affumed the pompous title of fearchers after truth. The illufion is at length vanifhed, and philofophers are grown more Proinde colore cave, ire. D L icrct. 40 DIALOGUE'!, cautious arid difficult, and examine one another with nl violence than the Egyptians did their dead before t would allow them the honour of fepulture. Come, the Marchionefs, explain me this fyffem of Defcartes, fhall not be lo difficult as not to receive pleafure fron e ven if it be iuch a cue as you make me expert. It is p Madam, anfwered I, but that every thing lhould ill this time be propoied to you under the form of a phili phical fyilem. Suppofe to yourfelf, that all the matter, of which whole world is compofcd, was from the beginning divi into exceeding fmall and equal particles, of a figure ne; refembling a dye. Suppofe too, that fome of thefe p tides turn round one point, and fome another, and t at the fame time they all turn round themfelves lik wheel, which, while it is moving to any particular fj makes many revolutions about its felf. The points ah which thefe particles turn are the (fars, the moll lumim and fhining points in the univerfe, and which will h you to conceive it full of vortices , for this is the name t is given to any mafs of matter that is whirled round a pc or common centre, juft like the circles of water in a ri\ or the dull that flies when it is agitated by the wind, [ believe you will not fcruple to grant the fun a vortex of own upon my aflertion, fince he is not at all infeiior any of the ftars. if you defire it, anfwered the Marc onefs, I will go farther, and allow him the largeft i moft magnificent vortex in the world. For I think highly deferves it, to whom we havefo many obligatio Philofophy, anfwered I, is lefs interefted, and has no m partiality for the fun, than for the leaft ftar in the mi way. It is fufficient if you grant the fun a vortex , b with efore one, carta efro On Light and Colours. 41 ,t it will. From this vortex, you fliall iee the fun him- arife; for hitherto I have fuppofed him and the ftars the better to aflifl your imagination; and with fun, all the charms of light and colour, and I know what befides. In fhort, it is like an inchanted palace, It is ere you have only need to alk what you want, and it Jd i i appear in an infant. plii iVhat I have granted you is fo little, replied the Mar- onefs, that I cannot flatter myfelf with the hopes of lo lid at a happinefs as you flatter me. The mathematicians, . wered I, are faid to refemble lovers. If what you. re mt them at firf be ever fo little, they know howto ke fo good an advantage of it, as to lead you infenfibly ther than you ever imagined. Now you are to confider it this philofopher, to whom you have granted what 1 think fo flight a conceffion, was a mathematician. I ! |ve as little Ikill in the artifices of love, faid the Marchi- ;fs, as in thofe of philofophy and mathematics. But it nconceivable to me that any thing reafonable can be nduced by thefe vortices , which after all are nothing t colledlions of extremely fmall particles, that keep whirl- n ' round a point at the fame time that each of them turns jimd itfelf. They may; whirl on forever, and I believe it will be the chief of their bufinefs. Who would ever ve imagined, anfwered I, that the accidental meeting b! a hero and heroine in a romance, and a certain Je ne d qttoi, that he difccvers in her, could have fupplied itter for twenty volumes ? and yet there are many in- (nces of this, perhaps too many, in a nation very near r own. And without giving the heroes any trouble in is afFair; what an infinite number of things might there proauced from that Je m fgai quo:, that every one fee& D^2 12 dialogue I. in you ? Let us fee at prefent, faid the marchionefs : what Defcartes’ vortices will produce ; for after theft twenty volumes, I lhall begin to think every thing poffi- ble. Thefte particles then, continued I, in the figure of a dye, which you now begin to have a better opinion of, whirling in this manner round themfelves, mull make terrible collifions, and, confequently, break the angles or points of each ; wdftich deprive them of a power of turning freely round themfelves. You know, Madam, that, if any thing be taken away from the corners of a dye, it will grow round, and in proportion as the angles of what re- in tins of the dye keep fucceffively diminifhing, it W’ill gradually approach Hill nearer to the lhape of a ball. And this you are to believe was the cafe with thefe particles, which by continually firiking againfl one another, were at length changed from their firll figure of a dye, to that; of fo many little balls or globules. The matter which a. rofe from the fhavings of thefe angles, and which by its continual collifion mutt neceffarily be reduced into very fmall and volatile particles, did not remain idle, but had its proper office. It immediately declared open war againfl the vacuum of the atomifts, and threatened to deflroy and baniffi it from the univerfe, wherever it w T as to be found. The firft undertaking of this matter was to fill up thofe little voids which othervvife would have remained between the globules; for though they touched one another, yet 1 there mufl have been fome empty fpaces between them arifing from the nature of a globular figure. But with- out the affiftance of this matter, there would have remain- ed a much more confiderable void in the centre of the vortex. The globules were reduced to a much fmaller On Light and Colours. 4 ? j Gze than they were at firft; and were proportionably re- moved from the centre, by a law common to all bodies ■ j (moving in a circle ; which recide as far as they poflibly can from that point about which they turn. This matter then : ; run into the midft of the vortex in order to fill the centre of : it, and began itfelf to turn round together with the globules, andanimate the reft of the vortex. This fubtile and volatile : fubftance, which is called the matter of the firft element, or the fubtile matter, forms nothing lefs than the fun and liars in the centre of the vortices ; as the globules that turn round :rk them, and which are called the matter of the fecond ele- :::■ meat , furnilh matter for the heavens; and though the di Cartesians have deprived it of that tranfparency and adamantine folidity that formerly rendered it fo venerable ■:1s among the antients, they have taken care however to a- tone for this injury, by making it the original of light,, thai and by this means it has gained more than it loll. What, cried the marchionefs, are we got already to ; the origin of light ? Your heroes and their twenty volumes : T have made a very bad ufe of their time, compared with j us. If you give a farther attention, anfwered I, you will It (find they have made- a much worfe ufe of it, even than you believe. The fyllem of Des Cartes prefents you a 1( j fcene, fuch as, I believe, you never beheld in the fineft and moll fplended opera. The whole extent of the uni- verfe is fown and filled- with innumerable vortices joined to one another of different fize mid figure, but all of them nearly round. Thefe keep each other in a- mutual equi- librium by their reciprocal preflure. In the midll of every one of thefe vortices is a liar or a fun, that is to fay, a large ball of fubtile matter that drives to dilate Itfelf, and et Ipreffes the vortex all round. This preflure of the fubtile communicated to the globular matter , or that of the fecond B 3 44; DIALOGUE I. element, gives birth to light according to the opinion of Des Cartes. The different bignefs of the ftar, and much more its diftance from us, caufe the light of it to appear more or lefs lively to our fight: and hence it is that the fplendor of the fun in whofe vortex we are • w ith fuperior Haze Dims the pale lujlre of the farry rays. It is believed that Syrius, though his diftance from us be more than two millions of millions of Englilh miles, according to the calculation of a celebrated mathematician, is yet the neareft ftar that we have ; becaufe it appears larger than any of the reft, and its lively and fparkling light makes the longeft refiftance againft the dazling fplen- dor of the fun. I fuppofe, Laid the Marchionefs, that out of partiality to your Syrius, you omit that ftar which the peafants call Diana, and the poets the harbinger of the rifing day, and to whom, comparing earthly with heavenly things, they j rive the fame honours as to Aurora. You muft take care, anfwered I, not to confound two things together, which are very different from each other, as a body that is lu- minous in itfelf, and one that derives all its fplendor from another; or in other words, a fun and a planet. It is true, that all the planets, as Venus, which in the language- of aftronomy is the fame as your Diana, Mercury, Mars, Jupiter, Saturn, and our earth itfelf, were antiently fo many funs, and may, perhaps, for who can penetrate into the fecrets of futurity ? hereafter be again reftored to that honour. I have not yet mentioned to you another fpecies of matter which is called the matter of the third element , and which has occafioned the greateft and moll remarka- ble revolutions that are left upon record in the annals of the Cartefian philofophy, Among the particles of that On Light and Colours. Back 45 r ubtile matter of which the fun is compofed,’ there are fome :hat by their rugged and irregular figure unite and cling ;ogether, and by thefe means form maffes that are fome- t times bigger than our earth. Thefe maffes are driven away from the fun, and repelled to his fuperficies. The preflure that communicates itfelf from the fubtile to the globular matter , or in other words, the light is interrupted fi ts !in that part of the fun’s fuperficies where thefe maffes are lilts, placed, and from hence they appear to us as fpots, which, iturning round with the fun, eclipfe part of his fplendor and glory. Flattery perhaps made certain courtly aftro* nomers take thefe fpots for little planets, that get betwixt b the fun and us, and made ufe of them to tranfport the families of thofe princes to heaven, from whom they ex- pected fome little penfion on earth in exchange for the in- veftiture of a thoufand planets which they with great r j confidence promifed them. Philofophical politenefs tranf- formed thefe maffes into patches upon the fun’s face ; if you are better pleafed with the idea under which they were reprefented to the queen of Pruffia by the famous Mr. Leibnitz, who thought that philofophical terms fhould du Ee foFtencd for the ear of queens. The thing is too ferious to bear a jeft, faid the Marchionefs ; patches as big as the ^ ; earth might quite demolifh a face. Hitherto, continued I, our fun has been lucky enough to efcape this misfortune. The motion and agitation of the fubtile matter breaks and diffipates thefe maffes as fall as they are formed. There once appeared one of thefe fpots, which darkened the fifth part of the fun’s difk. This •was a mod; enormous and terrible bignefs, enough to make aftronomers tremble, and the whole vmrld melancholy The fun at laft difengaged himfelf, and got the better of it, fo there is now no reafon to fear any fuch unlucky ac- 46 DIALOGUE I. cident ; but all the other funs were not born under fu'ch favourable circumftances. There are eertain ftars which are confiderably diminilhed, fo that what has formerly been placed by aftronomers among thofe of the fecond magnitude, is now fcarce worthy of being reckoned a- mong thofe of the fixth. This mull be afcribed to thefe fpots which by length of time are fo increafed, as to form a fort of cruft almoll over the whole ftar, and confequently weaken its light. On the other hand, faid the Marcldonefs, might not certain ftars arrive to a greater magnitude, if the agitation of the fubiile matter was ftrong enough to diftipate part of their cruft ? You are throughly poffeftfed, Madam, an- fwered I, with the fpirit of Cartefianil'm : this fedt places its glory in conjectures, and you have made a very good cne. But what a terrible defolation would it make in the poor ftar, if this cruft fhould entirely cover it, as it too often happens, and Ihould be ftrong enough to refill the force of the fubtile matter that drives to break and diftipate it ! When this is the cafe, we may bid farewel to the fun, or ftar which has loft that place of honour which it be- fore held in the univerfe. Its light is fuffocated by the cruft, ; nd from a luminous and fplendid body, it becomes dark and cold The force of its vortex is confiderably weakened as it arofe from the fubtile matter , which has now no communication with the global Th equilibrium is broke, and confequently its vortex delfroyed. Some one of the neighbouring ftars carries it away with it and now become a planet, it is forced to whirl round at the mercy of the moft powerful. Thefe are the moft remarkable me- tamorphofes that can poffibly happen, and to which our metaphorical funs here below are no lefs fubjech When, thefe begin to lofe their luftre and have nothing left to inch icl ®r onj i a* leie 'i'm itiy not ioa ari ID- Oil no hi m; K ss If w If r On Light and Colours. 4? feed that paffion which fo agreeably flatters the pride of the fair fex, and which ought to be the fubjeft of your philofophy, they are carried away and-become flaves to another, which for their confolation they call virtue. Our fallen funs, anfwered fhe, have at lead: the advantage in this, that they acquire a fine name, and under the fhelter of that they with great authority condemn what is no longer in their power to pradtife, and in fome meafure re- cover their loft empire. But what confolation is there for a^luTTeriibTe 'fun above', when it is inveloped with a cruft, and changed to a planet ? The confolation, anfwered I, of not having an odious and imaginary empire after having been poflelfed of an amiable and real one ; the confolation, in fhort, of not growing like an old Sybile after having re- fembled one. This miferable metamorphofis of a fun to a planet, ac- companied however with fome degree of confolation, is pro- bably what happened to a fine ftar which we have entirely loft in the conftellation of Cafliopeia ; and this too, according to the Cartefian fyftem, was the fate of our earth, which was once emprefs of an extenfive vortex crowned with light, and one of the brighteft eyes of heaven ; but at length in- veloped with a deformed cruft, unhappily loft its power and fplendor, and was carried away by the immenfe vortex of the fun, as a ftraw in a river by the impetuo- fity of a whirlpool. In the fame manner, the other pla- nets that revolve about him, Jupiter, Saturn, Mercury, Mars, Venus, fell vidtims to his fuperior power ; nor could even the comets efcape, though thefe are planets of a pe- culiar nature which keep rambling from one vortex to ano- ther, and like certain people among us here below, rove from one country and government to another. And thefe DIALOGUE I. 48 vortices are the grand machine invented chiefly by Des Cartes, to guide the planetary danCe round the fun. Is the earth then, replied the Marchionefs, after a fhort paufe, like the other planets obliged to dance round the *un ? And do all the mighty preparations, you made with your matter of the third element, amount only to this ? The earth, anfweredl, does not need that concern which you fhew for her degradation from a fun to the inferior rank of a planet ; fince by this means fhe was dellined to give birth to you, who are but another name for the moft charming thing, that all the vortices of the univerfe put together could ever have produced. Is not this a fufEci- ent compenfation for her lofs ? If it was in the power of gallantry, anfwered the Marchionefs, to make her amends, yours would certainly do it. But what can ever free her from the difgrace of being obliged among the croud of o- ther planets to whirl round the fun like a ftraw, agitated by the caprice of a whirl-pool ? I am fenfible that you phi- Jofophers look upon the earth with great indifference, and fuffer it to turn round without regret ; but for my part — • Let it whirl round for this- time, anfwered I, upon the word of Des Cartes. Hereafter if you have a mind to be convinced with pleafure, we will read M. Fontenelle’s dia- logues upon the plurality of worlds. There you will fee a Marchionefs, -who exaftly refembles you in every accom- plifhment of mind, and whom you have nothing to envy but her philofopher At prefent you are to look upon the earth only as a compofition of the matter of the third element, which renders it opaque, and as a body which no longer fhines by its own light ; and by this means I be- lieve you will be pretty indifferent towards it. A gloworm, one of thofe reptiles that glitter by night in the country, is On Light and Colours. 49 much more worthy your attention ; whatever is not lumi- nous is nothing to us. You have feen, continued I, what fort of a thing light is : you fee too how the fun may continually fupply fo great a quantity of light as he does, without any expence to himfelf, which is what gave you fuch terrible apprehenfi- ons in the atomic fyflem. He has nothing to do but to prefs the globular matter, and this preffure cofls him no- thing of his own, and frnce it is communicated on all fides, we are to conclude that he is luminous quite round. The light, according to Des Cartes, is but a moment in pro- grefs from the fun to us notwithftanding the diftance of a million of miles. The globules of the lecond element are continued from the fun to the earth, like fo many firings of beads, and touch one another. In the inflant that the firfl in the firing moves, or endeavours to move, it muff alfo endeavour to move the laft. Juft as a pole, though ever fo long, in the moment that one end moves, the other moves alfo. The meaning of all this is, anfwered the Marchionefs, that by means of thefe vortices philofophers may make and give a reafon for every thing. In a moment’s time we have produced the fun, liars, planets, comets, the earth and light. I fuppofe we fhall form colours with the fame facility. Nothing more eafy to Des Cartes, I replied. As motion or a tendency to motion in the celeftial matter, raifes in us the fenfation of light, fo the different motions of this matter excite in us the perception of different co- lours, which are nothing but certain modes in which bo- dies receive light, and afterwards tranfmit it to our eye. Thefe modes confifl in the increafe or diminution of that motion, by which the globules of light naturally turn 5° DIALOGUE I. round themfelves, and which is called the motion of rota tion. Thus thofe bodies, whofe fuperficies is difpofed ii fuch a manner as confiderably to augment this motior of rotation in the globules of light which fall upon them and are thence tranfmitted to us, appear to our fight red : thofe which increafe the motion fomewhat lefs, appeal yellow: thole, which confiderably diminilh it, appear blue, and thofe which diminilh it in fuch a manner that thefe globules turn round flower than ufual, appear green ; and to conclude, thofe bodies, that tranfmit a great num- ber of globules of light without altering their motion, ap- pear to us white, and thofe feem black, which extinguilh them, and as it were abforb the light. Here then you have the origin of colours, do you defire any thing more ? It is only fpeaking; the vortices are as ufeful to Des Cartes as the cocao-tree to the Indians, which fupplies them with all they want. No, no, faid the Marchionefs, let us at prefent confine ourfelves to colours : I need only increafe or diminilh the motion of rotation, in the globules of light, in order to form the fhades of a fine filk, and variegate the parterre of a garden with the different beauties of hyacinths, ane- monies and violets, in fliort, to diverfify the face of nature juft as I pleafe. Rather, faid I, if this increafe or dimi- nution fhould give you any trouble, you need only fup- pofe the globules of light to be entirely deprived of all rotation, which we will grant them only in the very ac- tion of variegating your filk or parterre, or in other words, in being repelled from the bodies upon which they fall. You may freely choofe which of thefe methods fuits you beft. Each of them will equally ferve your purpofe. Des Cartes, feems to have had this too in common with the phy- td blii ttbd more! On Light and Colours. 5 1 : clans, that he thought it unworthy his fruitful imagina- ion to confine himfelf to one fingle method of making his lefignsfucceed. Notwithftanding your malicious infinua- ion, replied the Marchionefs, I think myfelf much obliged o Des Cartes for this copioufnefs. I dare fay it will not ' ail him in explaining how it comes to pafs that one body hould give the globules of light a certain rotation, and mother body a different one. You are not confined here 5 sa lieither, anfwered I, but have free liberty of choofing what method you like beft for the explanation of the thing in 'VP jueftion, either different figures of thofe particles of which ;he fuperficies of bodies are compofed ; or their different • lifpolitions, their different inclination towards each other, Dr their being more or lefs fmooth, and a thoufand other e filings that you may imagine to yourfelf. By thefe means iti iwill your dextrous philofopher compofe not only the finery of filks, and the variegated beauties of a garden, but all ■ fe the elegance of a Paul Veronefe or the delicacy of Titian; if ( and hence too arifes that lively bloom on your complexion, which perhaps not all the art of Paul and Titian could ever have imitated. I fhould not have thought, anfwered fhe, that the colouring of my cheeks would ever have en- tered into the Cartefian fyftem. It enters, anfwered I, into other fyftems more generally underftood, and of fomewhat more importance than thofe of philofophy. But even thefe muft receive great honour from the explication of fo beautiful a phenomenon. I proteft, faid the Marchionefs, that this great plenty of caufes, and above all the fimplicity that reigns through- out this fyftem, quite charms me, not to fay any thing of thofe difficulties which it removes in all the reft. I fhould £ be glad to fee how any other woman in my place would E Iri flip ofal T25 5 2 dialogue I. guard againft it. I am too well acquainted with the lar guage of ladies, anfwered I, not to believe you alreadl conquered. You have not fufficiently clofed your ears t the fong of this philofophical fyren, nor guarded you heai t againft the alluring pleafures in the luxurious garde: ' of this Cartefian enchantrefs. But you have forgot tha I yourfelf at firft condemned this precipitation in buildin fyftems, which cannot afterwards bear up againft the ob ftinacyof obfervators. Hypothefes, or imaginary fyftem cannot long refill the force of experiments, which ar juftly called by a man, who carried them farther than peF haps any one that may follow him, natural revelations A liar, even if he was as ingenious as he in Corneille’ comedy, will at laft be found out. I had no notion, faic ihe, that fo many things could have been produced fron fo little a matter, as thefe whirling particles, and I thin! upon this account a little precipitation might be excufed 1; : and all this moralizing laid afide. I am extremely fond of the Chinefe, becaufe I am told they effedt whatever they take in hand, with much fewer inftruments and lefs apparatus than we do. And I think French mufic much ! preferable to ours, becaufe by a few fimple and plain notes'! it touches the heart, and moves the paffions. Whereas ours, with all its divifions, fugues and fhakes, leaves us for the moft part in a tedious and ftupid tranquillity. Thofe, who for every little thing make ufe of fuch great machines, put me in mind of the dictators antiently eledted at Rome, with the utmoft folemnity, and who never omitted choofing a mafter of horfe for no other end, than to fix a nail in the capitol. You may add, faid I, fince you feek for examples illuftrioufly ridiculous, thofe kings of Perfia, who never eat, walk, or go into the feraglio, tillanaftro* 'D, dfrfl On Light and Colours. 55 oger, after many obfervations and calculations, has af- iired them, that it is a lucky time to undertake one or ither of thefe important enterprizes. If we had been in j’erfia, how many aftrologers, how many calculations, fnuft there have been employed before you could have rJl been made a philoibpher ! which I take to be a thing of J much greater importance, than the walk of a king. I am ■ afraid, anfwered fhe, that before the aftrologer had fi- ■ nifhed his calculations, my inclination for philofophy ■" would have left me. But thanks to my good fortune, ithat I was born in a country, where if we have a mind to :a f' walk or hold philofophical difeourfes, we may do either without giving the ftars or the (ky any trouble about it. You ought rather to thank your good fortune, Madam, anfwered I, for being born in a country w r here your charms are not like thofe of the eaftern beauties, confined to the narrow limits of a feraglio. With thefe reflections of yours, faid the Marchionefs, you will make me lofe fight of our colours, whofe variety charms me the more, becaufe the production of them cofl me fo little trouble. But how fhall we produce thofe va- rious colours which appear in looking through a certain glafs which I once faw placed over-againft a window ? per- haps you have fome other fort of motion to produce thefe colours which only appear to be in objedts, when they are looked upon through one of thefe glafies. You may form thefe, anfwered I, in the very fame manner as the firfi. You need only make the globules of light that pafs through the glafs you mentioned, which is called a prifni, turn round according to thofe rules you have already learnt, and according as the variety of colours which it produces require. As to that diftindtion, which you feem E 2 atei idle mui .not here d 'hoi hint m lira 54 DIALOGUE I. to put upon thofe colours which are really in bodies, an thofe which are fo only In appearance, Des Cartes will nc grant it you ; for he, as well as the atomifts, as you ma remember, affects, that there are abfolutely no colours i: bodies, and that they only appear to be fo. Thus for in fiance, betwixt the red on your cheeks, and that in th rainbow, or prifm , there is no fort of difference, only per ! haps it would be more pleafant to make obfervations oi one than the other. But after all, they are of the fame nature, and only apparent. Do you think, continued I. laughing, that fo many poets would have compared fint ladies to the rainbow, if there had not been fome refem- blance in their colour ? as, for example, one of the^greatefl philofophers in our time has done in thofe fublime verfes, where he is deferibing fome beauty who perhaps refembled you. # Tale in fomma tie gia qual di rubini E d'or ricca, e di gemme e d'ejiro adorno Sorger veggiam la matutina aurora, 0 qual ful variato e lucid arco Apparir fuol dopo nernbofa pioggia Di taumante la figlia ; allorche, i venti venti Si fan fofpefi a vagheggiarla e intanto V infano mar depon /’ ira, e s’achera. You fee, faid I, that one of the moll fplended and pom- pous fimiles, that the poets have in their whole collection, would have been guilty of too effential an error. Serioufly, anfwered the Marchionefs, I always thought that the colour on my cheeks, whatever it be, was really * As our author does not mention where he had thefe verfes, I would not venture to tranflate them from the Italian, fince I am not certain, whether they were not originally written in Englifh. On Light and Colours. £5 here, and that the prifm or the rainbow were only in ppearance ; pray explain this paradox to me, which, to A y truth, I am very much perplexed with; and deliver i ie-from the uneafinefs I cannot help feeling on your com- aring me to the rainbow, notwithftanding you made me . great compliment by this fine fimile. This, faid 1, is educing things to that fimplicity you feemed fo fond of, i>y taking away the diftindtion which you put between eal and apparent colours. But the intereft you have in his diftintfion, and your felf-love, that makes you trem- )le at the thoughts of lofing your rofes and lilies, to peak in the paftoral ftyle, has at prefent got the better of ^our love of fimplicity. I will engage there are many adies who would have the fame fcruples : but after all> ^ou cannot with honour adopt a fyftem without being willing to admit the confequences. We’ have before faid, that there is in bodies only a certain difpofition and tex- iture of parts, and in the globules of light a certain rota- tion which thefe parts give, them. Thefe globules in a (certain manner tickling and Ihaking the nerves of the re- \tina, which is a very thin membrane at the bottom of the jeye, give us the idea of fome colour, which we by the help o£ our imagination refer to the body from whence thofe globules of light are derived to us. But I think we 1 are called to dinner, and it is time for us to fee what tafte our imagination will help us to give the foup. Our ima- gination, replied the Marchionefs ! I do not know whe- ther he, who has laboured thefe three hours to give it a real tafte, will be very well pleafed with you philofophi- cal gentlemeq, who would reduce every thing to mere appearance. I dare fay, anfwered I, that he will give himfelf very little trouble about fuch a trifle as a philofo- E 3 $6 DIALOGUES 6c. pliical opinion. But however, if he did, he muft bear i for as bodies are in reality without colour, fo they a likewife without tafte, fmell, found, heat, cold, and ev> when they appear moft luminous, without light. The Marchionefs was very defirous that I Ihould expla this paradox more fully : but I allured her, that if \ ftayed till the foup wanted heating again, not the lint and moft limple explications in the world would help ot imagination to give it a good tafte. She was fully coi vinced of this truth, and we ended our difcourfe in tl manner of Homer’s gods, who after their confultatioi are fure never to forget their ambrofta. That qualities, fuch as light, colours, and the like, are :tu not really in bodies. Metaphyfical doubts concerning Ipo our fenfations of them. Explication of the general prin- r cc ciples of optics. L L the while we were at dinner, the Marchionefs entertained herfelf with making the globules of light turn round, fometimes one way, fometimes another, as the different colours of the objects before us required, and looked upon herfelf, as die faid, to be the emprefs and arbitratrefs of nature, fince {he was polfeffed of materials to diverfify it as many ways as die pleafed. As foon as dinner was over, and we had returned into the garden, I am ready, faid {he, to deprive the foup of all tafte, and willingly renounce every colour, even what 1 had the greateft fondnefs for. In diort, I will be quite a Cartefian, provided you can fumidi me with good reafons. Thefe globules, it is true, lead me to ftrange confequences, but perhaps they may furnifh me with fome expedient to evade them. You treat philofophy, anfwered I, as attorneys do the law. But there is no expedient that will hold good at the fevere tribunal of reafon. Not all the monarchs in the univerfe, nor all the beauties which are far more pow» erful, can influence the impartial judgment of philofophy, nor induce it to interpret the lead text in their favour. This is a trial, a mortification that Des Cartes will make you undergo in your novitiate of philofophy. But are 5 8 D I A L O G U E II. you terrified at fo fmall a hardfhip as this ? Take courage and fear nothing ; you will at lafi. add to the pleafure you receive from your fenfes, that of contending with them, and giving them no credit. Hitherto, faid the Marchionefs, I have only the morti- fication of feeing that we are under a perpetual delufion, fince, if what you fay be true, things appear to us very different from what they really are. Bodies appear to us of a certain colour, whereas there is really nothing elfe in them but a certain difpofition of parts. They feem to us to be hot, cold, and yet they are poifefTed of none of thefe qualities. Really I cannot help thinking, that we are in ' a very ftrange condition. It is certainly very tlrange, an- fwered I. Our knowlege can make but very little progrefs, unlefs it be conduced by the fenfes. They continually make us believe things, which a more refined fenfe, or our reafon, afterwards contradicts. You think, for inftance, that your hands, which have been the fubject of fo many fine verfes, are fmooth and polifhed ; and poflibly might be greatly offended, if any one fhould dare to difpute them this quality. And yet if you were to look upon them through a microfcope, you would be furprized to fee a great number of pores that feparate the texture of them, and to find that they are covered with feales like thofe of a fifh. You would difeover in them cavities, promontories ; vallies and hills, for the abode of a nation of little animals, who perhaps fpend their life there. And to increafe your wonder, you would be prefented with the fight of rivers and feas. In fhort you would not know them again, and you would be obliged to confefs that they are very diffe- rent from thofe which your poets deferibe. Nature, faid the Marchionefs, has done us a great favour in not making On Light and Colours. 59 our fenfes too refined. It would be very bad for us, if our touch was exquifite enough to feel all that the micro- fcope difcovers to our fight, We fhould certainly be ex* tremely unhappy, anfwered I, if our fenfations were fo perfect, that in handling the fmootheft furface, our touch fhould fail us at every pore, and every little eminence fhould make us fhudder. It is to the filence of our reafon, and the want of more refined fenfes, that we owe our per- ceptions of pleafure. And he gave a very juft definition of our happinefs, who affirmed, that the moft tranquil poffeffion of pleafure confifts in our being agreeably de- ceived. It muft be confeffed, replied the Marchionefs, that our fex is greatly obliged to the complaifance of philofophers, who, notwithftanding they are fo well acquainted with the nature of our fuperficies, are fo genteel as to behave to- wards us like the reft of mankind. But if I had a mind to pleafe any ignorant perfon, the very firft thing I would do, fhould be to forbid him the holding any correfpondenee with thofe gentlemen who deal in microfcopes ; for thefe might do me a very great prejudice. Not all the micro- fcopes nor all the philofophy in the world, anfwered I, could ever hinder your appearing agreeable to the naked eye, and even a Cleopatra might be contented with this. Virgil makes Corydon warn his Alexis not to confide in his beauteous colour. But I may freely give you leave to con- fide in your hands. As our fenfes are not microfcopical, fo neither are our hearts philofophical. It would be very bad for us, if our pleafure was in the hands of philofophers, and if beauty, in order to prove its exiftence, muft ftand out againft all the experiments of a naturalift. This is juft as if the chafti- 6o DIALOGUE II. ty of a lady fhould depend upon the ill-grounded fufpicion, and diligent enquiry of a jealous hufbatid. Thefe two lcinds of men have this in common, that they both equally tend to dcftroy the moft valuable things in the world. But philofophers, faid the Marchionefs, deflroy without mercy; for they can leave but very little elfe to bodies, after they have deprived them of colour, tafte, and thofe many other qualities which they have taken from them. They leave them, anfwered I, in pofieflion of extenfion, that is, length, breadth, and depth ; impenetrability, motion, figure, and all the fine things that mathematici- ans and mechanics deduce from thefe qualities, upon which 1 1 could produce you fo many formidable volumes, that all which has been written upon the Crufca , would feem, com- pared to thele, no more than a king’s declaration of love. Do not you think it enough for bodies that they are no more than bodies ? Befides, what philofophers do with re- gard to thofe qualities we were fpeaking of, is not properly , a definition : they take nothing away from bodies, but what was falfely applied to them, and what they had | uniuftly pofTefled ; and reftore thofe qualities to us, to whom they rightly and properly belong. Prefcription 1 has at prefent no influence on philofophy, as it formerly had. If a lover, for example, fhould fay, that there was hope in a certain favourable glance, which had darted |i on him through a fan, what harm would a philofopher ' do, who, without deftroying either the hope or the glance, fhould tell him that there was nothing in the glance, | but a particular motion of the eye, cau fed by certain muf- || cles, either from a principle of pity, or if we would trace the thing to its original, coquetry: but that the hope was entirely of himfelf, and excited by the means of that ■■i mti gmmmmm 6 1 On Light and Colours. ■>■121102. Juft in the fame manner, when we are pricked with a needle, the pain is entirely in ourfelves; and there is nothing in the needle but a motion by which it disjoins and lacerates the fibres of our body : this feparation is the caufe that we feel pain. In fhort, bodies are only matter, and confequently can have no properties but what ■ . 5 ■ / depend on matter; and thefe the Cartefians have con- fined to extenfion, mutual impenetrability, diverfity of figure, and a different difpofition of parts. And thefe are fufficient to give bodies a power of exciting dif- ferent ideas in us, as thofe of light, colours, tafte, and the like. It is not neceffary, for inftance, that colour fhould really be upon the furface of a body, in order to make me fee that colour, any more than it is neceffary for pain to be in a needle, in order to make me feel it when I am pricked. It is fufficient that as the needle caufes a certain difpofition in the fibres of my body, by the means of which I feel the pain, fo that particular rotation, which is in globules repelled from the furface of a body, fhould caufe another motion upon the nerves of the retina, which car- ried from thefe to the brain excites in me the idea, or, as they call it, the fenfation of colour. Thus, if in any body there be a certain motion by which it preffed the globules of the fecond element, and thefe globules be carried to our eye, they will raife in us the idea of light. A certain con- figuration of particles, or perhaps certain little animals which are in bodies, by playing upon the nerves of the tongue in fuch a particular manner, raife in us the fenfa- tion of fome tafte. Thefe fenfations are generally raifed in us by means of certain bodies, and becaufe we fee nei- ther their particles nor the little animals which are in them, the globules of the fecond element, nor the im- preffion which is made upon our nerves, we afcribe to 62 DIALOGUE H. thofe bodies both light, colours and tafte, which in real! ty are only in ourfelves. Reafon at length convinces u of the illufion that our imagination continually puts upoi us, and allures us, that the delighful and hitherto undefinec tafte of the pine-apple, the pleafing verdure of a mea' dow, and even the light of the fun which animates and revives the whole univerfe, are all our own. I underftand you, faid the Marchionefs; we are enriched at another’s expence, and are like antient Rome, which founded its grandeur upon the fpoils of the whole univerfe, Philofophy would be in a bad ftate, anfwered I, if its rights had no better foundation, than thofe of policy and ambition. I fee you have not yet a right notion of it. In order to convince yourfelf that philofophy is no ufurper, but only takes its due, prefs one corner of your eye with your finger, and you will fee on the oppofite part a round flame of a reddilh colour. In this cafe there is certainly neither light nor colour without your eye. The only rea- fon of your feeing them is the prelTure which your finger makes upon the nerves of your eye. The globules of light, which flow from the furfaces of bodies, occafion the fame effedt upon the eye as your finger, only their opera- tion is more impreceptible. The different difpofition and configuration of the parts of a body, are the reafon why the globules make different impreffions upon us. The power of a body’s exciting in us the idea of any particular colour, confifts alone in this difpofition, and the configu- ration of its parts. Is it not evident from hence, that if this difpofition be changed, the colour is changed alfo ? which could not happen if the colour was really in the parts of the body itfelf. Coral, which is of a fine red, if it be ground to powder turns pale. One liquid mixed with another changes its colour. The reafon of all this On Light and Colours. 63 , that the difpofition and configuration of the parts of hefe bodies are changed by being ground or mixt, and rom hence they tranfmit the light to us in a different nanner, and confequently our idea of the colour is chang- ed ; from no other reafon proceed the venerable -white ocks of old age ; the tranfient whitenefs of many animals if the north in winter. From hence too it is, that certain rofes in China are in the fame day both white and purple. • From this caufe arifes that furprifing variation of colour f which generally follows the change of pafiions in the ca« melion, which has furnifhed the moralifts and poets with fo many allufions, the antients with fo many fables, and the moderns with fc many obfervations. And what is it elfe but one difpofition which hinders us from feeing you igoddeffes when you firft rile, and another which gives you jto our fight and adorations after you have fpent two or three hours in the facred rites of the toilet ? I perceive, replied the Marchionefs, that there is nothing fecret to philofcphy ; we may hide ourfelves from men, but not from philofophers. And indeed to what purpole would it be for us to endeavour to conceal ourfelves from a fet of people who are quick fighted enough to difeover the globules of light endowed with a certain motion, and thofe nerves and fibres to which this motion is communi- cated and thence conveyed to the brain ? A fight which mortal eyes have uever yet penetrated into. But I muff ! confefs, I hand in need of your affillance to guide me ; through this obfeure labyrinth. I do not fee what relation all thefe motions have to any colour that I have a conception of. This is a thing which feems to toe quite different from thefe motions. Have you any better conception, anfwered l, of the relation between the idea of pain, and a fenara- F 64 D I A L O G U E II. tion of the fibres of your hand ? Or between the idea c hope and a certain motion in the mufcles of an eye ? An* yet you fee that thefe things are in fad connected, ani that the one is the caufe, or at leaft the occafion, of th other. You feek for more than it is pofiible to give you;! Unhappily for us, thofe things which are of the greatef importance to human knowlege are the moft doubtful Who can tell you in what manner objefts occafion certaii ideas in the foul, and how the foul on the other hanc gives certain motions to the body? how the foul which is unextended, yet is prefent in every part of our whole machine, and though incapable of being feen or felt, yet fees and feels every thing ? Philofophers can with a greai deal of eafe tranfmit the motion of the globules of light, or any other motion, to the nerves, and from thefe to the brain, where they all terminate, either by means of a fluid that runs through them, or a certain tremor raifed in them. Nay, philofophers will go yet farther, and tranf- mit this motion to certain parts of the brain which are imagined to be the feat of the foul. But how thefe mo- O tions, when they are arrived to the brain or feat of the foul, fhould produce in it different ideas, is an abfolute my fiery. This paflage, which in appearance is fo fhort, is to philofophers what the innavigable ocean was to the antients. What communication, what connexion can there be between body and foul, between extenfion and thought, motion and idea, matter and fpirit ? What fort of communication thefe can have with one another, is be- yond the reach of our imagination. The fame, anfwered flie fmiling, that .Eneas had with the fhade of his father Anchifes in the Elyfian fields. They mutually communi- cate the moft agreeable things in the world to one another On Light * n d Colours. 65 5™M great oubtfi Here eriai I wlii i Ut when /Eneas.^empts to embrace the old man, he ianifhes away and is diffipated into air. We P' a Y draw a fine allegory from this pafFage, anfwerea ivhich would have done great honour to a learned and ■nifty commentator of the laft age. Now in order to put our allegory in a clear light, and to let you fee on the ither hand that nothing is able to difeourage a fet of people nought up and educated in the midft of difficulties, fomc )f them will tell you, that there is a certain correfpondence or ’jore-eftabliftied harmony betwixt foul and body, fo that though they have no more connexion with each other, than a harlequin dance in our operas has with the death of Dido, or ! the fate of Rome; yet by virtue of this pre-eftablifhed " '.harmony, at the fame time that certain motions happen 'fin the one, certain ideas and defires arife in the other/ 1 In fhort, that they are like two clocks independent of each other, whofe weights are adjufted in fuch a manner, that ■ when this ftrikes one, that (hall always ftrike two, and fo on. Your Des Cartes will tell you that upon occafiom when bodies without us in the material world excite cer- tain motions in our body, the foul fees certain ideas in the intellectual world. So that in the material world, you have nothing but extenfion, and certain motions, and con- figurations, and whatever other qualities you poflefs, and which render you fo agreeable and charming, exift only in the intelle&ual world. Others will tell you, that by means of certain motions in the body, God reveals and difplays certain ideas to the foul. But they have fo little regard for any connexion between thefe motions and our ideas, that they affirm, we might as well hear with our eyes, or fee with our ears, provided the laws of the union of the foul and body were different from what they now F 2 ; 66 DIALOGUE IE ecre, which is not impoltible, fince vla e f e laws are merel arbitrary. One of the laws of this union ; Sj t h at w h e there are certain motions impreffed on one of n things. Two people, one of which fnould give a chief magiftrate the name of king, from wdiofe good or ill ad- miniftration depend the life and properties of his fubjedtsj and the other fhould give the name of king to a chief ma- giftrate, who is only the ratifier and guardian of the laws of nature, to which he, as well as the reft, is fubjedted: thefe two people would both agree in the found, by which they denote their chief magiftrate, but not in the idea which they annex to this found. Both you and I had a certain meafure at firft fhewn us, which though it appears to you of a different fize from what it does to me, yet both of us agree in calling it a foot, becaufe we are told that mankind diftinguifhed fuch a meafure by that name Ac- cording to this, which is the rule of our menfurations, we both fay that this tree is fo many foot high, though it may appear to me of a greater or lefs height than it does to !J literal h! , ivni 70 DIALOGUE II. you, and fo every other thing in proportion to the diffei j ent idea we may poffibly have of a foot. Who can te then, but you may appear to yourfelf, and I to you, lik'j one of Gulliver’s Brobdingnagians ; on the contrary eaci | of us may appear to my fight as fmall as a Lilliputiai does to yours, and who knows too but you may fee tht I whole world after the proportion of my Brobdingnagian, I and I of the fame fize as your Lilliputian ; fo that if it | were poffible for us to fee with each other’s eyes, which Would be a good exchange for me, you would defpife the diminutive fize of my Coloffufes, and I fhould tremble at the gigantic ftature of your pigmies. Wemayeafily tranf- fer the fame way of reafoning to colours. We here too agree upon names, but may very probably differ in things. Each of us, forinftance, calls the leaves of this tree green, becaufe we were at firft told that the colour of leaves was green; but it is poffible, that if things could appear to your eyes as they do to mine, you would be furprized to fee thefe trees and the whole country clothed in a colour which you perhaps might call purple or fome other. Be- caufe we fee that all men refemble one another in the make of their body, when they have all tw® eyes, one mouth, two legs, and two hands, we are led to imagine from thence that they mull all refemble each other in their ideas, and from hence arile many inconveniences in focie- ty which would not have happened, had men been a little more philofophical than they are. From hence it is, that a politician, when you are thinking on fomething quite dif- ferent from his projects, will plague you with a long ac- count of the end and intentions of all the privy councils in Europe, and the divifion which he has already made in Italy ; for he thinks it impoffible that a man, who refem- lin s e : : On Light and Colours. 7 1 es him in his outward appearance, fhould not equally itereft himfelf in his vifionary fchemes. From the fame aufe a lover will talk you dead with the hiftory of his ontinual fighs and hopelefs paffion. In fhort, this miftak- n notion gives birth to numberlefs other inconveniences n fociety. None greater, faid the Marchionefs, than the jhilofophers who endeavour to reverfe the ideas that man- kind have formed to themfelves, and make us believe that we do not all fee the fame thing of the fame fize and co- lour. Cannot you find fome method to explain to me whether the world really appears fo different to different perfons, as you fay it does \ It is not poffible, anfwered I, to find fuch a method as you require, unlefs there could be any one meafure which all men were certain of feeing abfolutely of the fame fize, and certain colours which, in the fame manner, they could be affured, appear the fame to all eyes, and to thefe they might refer all other colours, as well as all other fizes ' to the meafure. As thofe two people who make ufe of the fame word king to fignify their chief magillrate, though the one be in effect very different from the other, can ne- ver come to a clear explanation of the different ideas they would annex to the fame word, unlefs they define and compare it with other words, and more fimple ideas, fuch as both parties are agreed upon. Now red, yellow, and the fmalleft imaginable meafure, are in themfelves fuch fimple ideas, that they can neither be defined nor com- pared with other ideas more fimple. Therefor we have no way of knowing whether all men have the fame con- ceptions of them, or not, fo that mankind are much to blame in being fo confident that the world appears in the 12 D I A L O G U E II. fame manner to all, for it is a great chance but they s| miftaken in this affair. But what ill confequences can there poffibly follow fro 1 our faying that the world appears to every fingle man di 'j ferent from what it does to all the reft ? Nay, if we fhoui I go farther, and fay that even the world itfelf does not e> I ift, and that all thefe bodies, this fun, thefe ftars, an' thefe fine ladies, are nothing elfe but dreams and appear ances. There is one philofopher who affirmed, that «j perfon need only to have flept once in his life-time, to bi l convinced of this. So that while fome are difputing about) the manner in which the world exifts, others abfolutelyl deny that it exifts at all. But though I have flept more than once in my life, I will not preach up a fyftem to you which would mutually deftroy us both. I will rather af- fure you, that though we really fhould fee the world in different manners, yet I am willing for my own intereft to confult your prefervation. They will all agree in faying, that this tree is fo many feet high, and the leaves green, and that you are of a juft height and a fine complexion ; and does not this difference of ideas diffufe an infinite vari- ety over the whole fyftem of nature, which feems even in the minuteft things to take a pleafure in diverfifying her- felf a thoufand ways ? but what a pleafure muft you find in imagining yourfelf to appear to fome under the height of a wax baby, and to others as tall as the image of Flora at Farnefe ! to fome of an azure complexion, with the green locks of a Nereid, and to others of a vermilion dye, and adorned with the rofy treffes of Aurora, and under thefe different afpedts, to be agreeable to all, and adored under various forms, as the goddeffes formerly were among the antients. I muft confefs this imagination, that every fin- Ok Light and Coloitrs.. 73 e man fees the face of the world in a manner different om all the reft, though, if you will have it fo, it be a Dubtful point, gives me fo much pleafure, that I make a fcruple of carrying it beyond fize and colours, to tafte, .neb, and all other qualities. I faid, if you will have it fo, aly out of complaifance to you; for if it be confidered ow very different the nature of things is from what it ,, r ppears to our fight, fince we reckon, for inftance, thofe odies to be fmooth and folid, which are in reality full of ^ ores, cavities, and rifings, and imagine them to be en- ued with colour, tafte, and other qualities which exift nly in ourfelves : when we confider too that the fame bo- ies have a different appearance according to their diftance nd the other circumftances in which they are feen ; when II this, I fay, is well confidered, I do not know whether re may not affirm that every fingle man fees them in a dif- erent manner from all the reft, and that our judgment ; as much deceived in fuppofing that the fame things raife he fame ideas in different perfons, as it evidently is in the ither refpeft ; at leaft we may reafonably doubt whether t be not fo. You will fay perhaps, that this is raifing loubts and queftions to hide our ignorance. But it is how- ;ver one of the parts of a philofopher to fearch for motives lpon which he may form rational doubts upon things, or ather, fuch is our misfortune, this is the beft part of phi- iOfophy. However, we every day clearly fee that the ame objects do in effeft appear differently to different per- bns : not to fay any thing of the more important affairs )f morality, law, and politics, where what is efteemed in )ne nation an objeft of veneration and refpedl, is reckoned candalous and deteftable in another. Did not the ladies n one age drive all the colour out of their cheeks, and net 74 D I A L O G U E II. , afFeft a pale languid look, which were capable of infpi ing the mod lively fentiments, at a time when a painti face would have been as Ihocking as a fury. But in tl next age, this very fury becomes a Venus, and inftead llghs and fine fpeeches, the pale beauties are recommends to the care of a phyfician, or the ufe of Spanifh woe Were not the very fame graihoppers, that weary us wit their troublefome chirping, called by an ancient poet tl fweet harbingers of the fummer ? There are whole natioi who efleem black teeth a Angular beauty, and others wh paint one eye white, and die other red or yellow. I fome other countries, a beau i'acrifices and gafhes his fac to appear more agreeable to the eyes of a brutifh creature who is alone the millrefs of liis heart. An olive complexi on joined to a long head, a pair of deep funk black eyes a flat nofe, and the feet of a baby, are charms that mak great havock in the hearts of the Chinefe, and occafioi whole volumes of gallant verfes and love epiftles. Our Ga latea’s and Venus’s would not get fo much as one bille. doiiXy or a Angle ode there, but would be looked upon a: mere caricatures. In the fame country, learning is a ftep to the higheft honours of ftate, and there is more ceremony in making a dodtor there, than the Polanders ufe in eledb ing a king. Are not mufic and dancing, which are with us, as antiently among the Greeks, an exercife for perfoni of the firfl rank, looked upon in PerAa, as they formerly were at Rome, as fcandalous employments ? And would not the fame ladies, who caufe fo many commotions and difturbances in Europe, be clofe conflned in a feraglio and guarded by eunuchs in the eaftern countries? If you will not confent to admit a different appearance of things be- tween men, yet you muft allow it to be fo with regard to On Light and Colours. 7 S tations, as for inftance, between us and the orientals, un- efs you will except fome particular follies which feem to lave ufurped a more extenfive and univerfal right over nankind. The antients Greeks, the Romans, Orientals ■ md Americans, though feparated from each other byfuch aft t rafts of land and fo many feas, yet all agreed in the idiculous notion, that when the moon was in an eclipfe, which is occafioned by the fhadow of the earth, that de- prives it of the fun’s light, flie was in great danger, and j aboured extremely hard, and imagined they could be of fervice to her by howling, rattling with their timbrels, and naking the moft horrible outcries and noifes they could poffibly invent. I find, faid the Marchionefs, you begin to grow a little ' more moderate after this philofophical enthufiafm which had carried you fo far, that you endeavoured to reverfe the whole order of things. But you have now confented to grant, that we think alike in thefe opinions which you call ridiculous. As to all the reft, I am very well fatisfied, if you place this difference of ideas at fo great a diftance as is between us and the Oriental countries. In order to make you ftill eafier, anfwered I, we will at prefent place thefe different xvavs of conception at a dif- tance ftill greater, and in proportion as you grow a greater proficient in philofophy, we will bring them gradually nearer to us, till at laft we will agree to put fome differ- ence between your ideas and mine, and from thence be- tween the two eyes of fome perfons to whom the fame ob- jeft appears bigger when feen through one eye, than it does when looked upon by the other. How is this poffible, faid the Marchionefs ? There is no end to your vifionary fancies, and you feem refolved to 76 DIALOGUE II. put me to the utmoft proof of my credulity. Not coi tented to make a difference of ideas between different pe fons, you carry your notions fo far as to make this diffei ence between the two eyes of the fame p-erfon. I mu confefs, I think this a very daring way of proceedin'. Did not Gaffendus, anfwered I, one of the celebrated ph Jofophers of the haft age, affirm that he faw the charadtei of a book larger through one of his eyes, than the other You fee the fault is not to be thrown upon me, but upo; the eyes of Gaffendus. You would find many other per fons with theft fort of eyes, if they were but as curious ii examining their fenfes as they are diligent in making uf of them. To fome perfons an object is laid to appear green when looked at through one eye, and yellow or blue, wher, feen by the other. But do not we fee every day, thal what one perfon efieemeth cold, another calls hot ? Oi rather do not we ourfelves think the fame thing to be cold or hot, according to our different difpofitions? Would not the very fame thing that Milo might have thought ftnooth as a mirror, appear rough as a nettle to that lux- urious youth whofe bed was ftrowed with rofes, and who could not fleep for a whole night, becaufe a fingle leaf happened to be doubled ? And do not thefe different fen- fations which are fo extremely oppofite, as hot and cold, fmooth and rough, proceed from a different difpofition of the fenfitive organs; from a different affe&ion of the nerves, or the more or lefs delicate texture of the parts ap- pointed to carry thefe fcnfatiom to the brain ? and is it not very probable too, that thefe differences may be in that membrane of the eye, upon which the images of ob* je&s are depictured, and in the filaments of the optic nerve which tranfinit thefe images to the brain ? Hence it would On Light' and Colours. 77 illow, that as we receive different fenfations of hot, cold, , mooth, and rough, we Thou Id find the lame difference in - ,ur fenfations of colours, and the like. In order for me to enter into your fentiments, faid the l,i larchionefs, you mull explain what you mean by faying pi fat the images of objedts are depictured upon the mem- ; s irane of the eye ; and that the optic nerve tranfmits thofe ! nages to the brain ? Do you know, anfwered I, that an Explication of this will be no lefs than an explication of a r : f ifion itfelf ? So much the better, faid fhe : indeed it feem- d pretty firange to me, that after you had fpoke fo much, pon the different ways in which it is pofhble for us to fee, .. on fhould be filent upon the manner in which we really jj f be, I will not defer this explication any longer, anfwered jj \ , and I fnall be extremely happy if my fhewing you in ; vhat manner you fee me, may induce you to look upon f Joe in a different way from what you have hitherto done. 1 Light is principally fubjected to the two accidents of 'eflexiov. and ref 'aft ion. Reflexion , according to the Car- efians, happens when by collifion of the globules of light ivith the folid parts of bodies, thefe globules are repelled pack again, juft as a ball rebounds when it is ftruck againft he earth. And it is by this reflected light, that we fee ill bodies, the moon, the planets, heavens, and every hing elfe, except the fun, ftars, fire, and all thofe other bodies here below, which fhine by their own light. Re- daction is caufed when the globules of light in pafling hrough air, water, glafs, etc. meet with the pores and :avities of thofe bodies, fo that the ray, which is only a :hain or feries of globules, breaks and is turned out of ts proper path, and takes a different direction in its paf- !age from what it had before. Pellucid or tranfparent G 2 78 D I A L O G U E II. bodies which fufFer the light to pafs through them, fuc as water, air, diamond, and glafs, are called medium i Hence refraction is faid to happen when light pafles fror. one medium to another. And this refrattion is greater o lefs, that is, the rays are more or lefs broken and turnei a fide from their path, in proportion to the different den fities of the mediums through which the light fucceflively pafles. Thus for example, the rays are more broken ii palling from air into glafs, than in palling from air t( water, becaufe glafs is much more denfe than water; anc for the fame reafon they will be more broken in palling from air to diamond. If this was a proper time, faid the Marchionefs, to make criticifms upon poets, it might be faid, that TalTo has not exprefled himfelf very accurately, when fpeaking ol Armida, he fays, As limpid Jireatns tranfmit the unbroken ray , etc. Poetry, in thefe verfes, does not feem to agree with optics, which will not allow that a ray can be tranfmitted un- broken. Taflo perhaps, anfwered I fmiling, would be underttood to fpeak of thofe rays which fall perpendicularly upon water or chryftal, that is, without being inclined, with regard to the furfaces of thofe mediums , either to one fide or the other ; as a threed would fall upon the ground if it had a weight fattened to it : for in this cafe the rays pafs on without being broken, and continue to proceed in the fame path as they firft fet out in : but the truth is, that poets do not addrefs themfelves to philofophers nor to you, •who have nothing but refractions in your mind : but they write for the people, and confequently mutt often make ufe of vulgar prejudices and opinions. And provided the images be lively, the paffions ftrong, and the num- On Light and Colours. 79 iers harmonious, we may pardon them a miflake in op- ics. What do you think of Ovid, who has perhaps rretched the poetic licence too far, and made the lun in ; . day run through all the figns of the Zodiac; whereas r :; .ccording to the exact rules of aflxonomy, his diurnal courfe :-j i confined to about the thirtieth part of only one ngn ? ' n the fecond book of the JEneis, that mafter-piece of lub- -5 ime poetry, there is a very fine image, which, if examin- :• d by the law’s of optics, would lofe all itsjuftnefs. tineas, a .fter he had been allured by Hector in a dream of the ir- a separable ruin of his country, afcends a turret, and there lifcovers the treachery of the Greeks, whofe dreadful X -frects appeared from every quarter. The palace of Dei- yihobus already levelled to the ground, his next neighbour a Jcalegon on fire, and the flames of that city, which a ten •ears fiege had attacked in vain, dreadfully reflected by he waves of the lea. Now in the fituation in which Tineas < lood this could not poflibly be ; for the opticians will a ell you, that in order for him to fee the flames of the city . hine upon the fea, the fea mnft have been placed between -[ aim and thofe flames, which it was not. But who would j not excufe this error, which can be fecn only by a very few, for the fake of thofe flne verfes which all the world admires ? But to return from poetry to phyflcs, a tranfition which jrou have rendei’ed very familiar to me, the manner in which the rays of light are broken in palling from a rare to a ilenfe medium, as from air to glais, is different from what t is when they are tranfmitted from a denle to a rare me- Hum, as from glafs to air. I would be underftood, al- ways to fpeak of the rays which fall upon, thefe mediums obliquely, and with fome inclination ; for as I mentioned to you before, thofe rays which fall perpendicularly dw G 3 So DIALOGUE II. not fuffer any deviation. If you fuppofe then, that a ra of light coming from the air fhould fall upon the furfac 1 of a glafs, it will be broken in fuch a manner, that afte its trajedlion, it will be lefs inclined to the furface of th glafs, and immerging will approach nearer a perpen dicular. After the fame manner, a ray of light proceedin, from your eye would ftrike the middle of this bafor. provided it were dry. But fuppofmg it filled with water as it now is, the ray could not continue its courfe diredH to that point as at find, but in its tranfmiffion through th water would be bent in fuch a manner that it would fa on one fide, and ftrike the bafon in a point nearer to us Thefe are all the lines and figures that I will draw you, ti explain the prefent fubjedt. What need is there of lines and figures, replied tin Marchionefs, to underftand that a ray of light paffinj from air into water or glafs, will be bent in going toward: it, and approach nearer to a perpendicular? And doe: not the contrary happen, when the ray paffes from glafi into air? Yes certainly, anfwered 1; the ray in this caf< is more inclined after its t inject ion to the furface of the air, which immediately touches the glafs, it becomes more un- like a perpendicular, and places itfelf as it were behind, the furface of the earth. Thefe ref rations of the rays of light which were known, though very imperfedtly, to the antients, and to the con- fideration of which we in great meafure owe the perfedfion of aftronomy, are the caule of an infinite number of ftrange and amufing phenomena, which we every day obferve ; fuch as objedts appearing out of their place when viewed through a prifni : an oar broken in the water, and t I k fur prize of feeing ourfelves deformed and crooked whei in a bath. This is the very thing, faidlhe, interrupting On Light and Colours. 81 ne, that I lately obferved when I was In the bath, and : was extremely furprized and puzzled to find out the rea- Ton of it. It is nothing elfe, anfwered I, but the refrac- tion which the rays fuffer in pa fling from air into water. Thefe refractions, befides what we have already mention- ed, are the caufe too why we fee the bottom of veffels and rivers much deeper than they really are, and that failors after a long and tedious voyage, have the pleafure of fee- ing and faluting the land, much fooner than they would otherwife do. This too is the reafon that the fun and full moon appear to our fight of an oval figure when near the horizon, and many other things of the like nature, which, proceed from hence, that the rays in their palfage fiom thefe objects to our eyes are refra&ed, and come from places ] different from thofe where the objects themfelves are. The eye, which is not fenfible of thefe refractions , always re- fers and tranfports the objeds to thofe places from whence the rays appear to proceed, or in other words, it fees them in the diredfion of the rays which penetrate and ftrike it. Hence it is, that the figure and fituation of things which are feen by refradled rays, come to be changed. If, with- out knowing any thing of the fcience of optics, the firfi time I had the honour of feeing you, a prifm had been placed before my eyes, which by refracting the rays which pro- ceed from you to me, had given them 'the fame direction which they would have had f they had come from the fky, you would certainly have appeared to me to have been tranfported into the world of chimeras, and incom- paffed with an infinite variety of colours, and I Ihould have intreated you to defeend, as Endymion did the moon, and addreffed myfelf to you in fome florid defeription of a Ihady grove or lonely vale, in order to tempt you from the ftars. And all this fine delufion would have been occafi- 02 dialogue n. oned by that direction which the prifm had given to th rays, which would have flowed from you to my eyes. I I fancy, faid the Marchionefs, that mankind alwayl look upon thofe, who are in a condition much fuperior ti their own, through certain /rZ/m, which make them ap pear as if they were tranfported to heaven, to revel upoi ambrofia, enjoy the converfation of the gods, and be fur. rounded with glory and happinefs ; whereas the more they are elevated above others upon earth, the more fubjed are they to the fport and caprice of fortune. This com- parifon will appear Hill jufler, anfwcred I, upon this ac- count, that as when we quit the prifm , we fee the objeds again return to their proper place : fo when we forfake the opinions of the vulgar, and fubftitute thofe of good fenle in their room, tbefe demigods appear nothing more than other men, and in a condition no 1 greatly to be envied. But to return to our fubjed : A philofophical eye every day difeovers an infinite number of ftrange and diverting phtenomena arifing from the change of diredion produced in the rays of light, not only by refracliohs but by reflex- ion too. From hence proceed all the wonders of concave glafles, by the help of which, that poet, who wrote a diflertation on the nature of bees, could difeern the fmall members and diminutive parts of that noble and induftri- ous infed, and magnified them to that degree that each of them feemed as big as a dragon. With thefe glafles too the veftals rekindled their facred fire, whenever it happened to be extinguifhed. From hence arofe the fables of Ar- chimedes and Proclus ; and ignorance and impollure have rendered thefe glafles one of the favourite inflruments o£ magic. But among the phenomena which arife from a change made by refledion in the rays of light, you will On Light and Colours. 83 -‘perhaps be furprized to find one which is every day prefent with you, and which perhaps you have never yet confi- F lered as a phenomenon, much Iefs a matter of wonder. ‘What phenomenon can this be, faid the Marchionefs, to Fwhich I have paid fo little regard ? It is, anfwered I, the ' image of your felf, which appears beyond the looking glafs r ' every morning, when you hold a confultation with the ^ Graces in what manner it will be bell: to give an artificial negligence to your hair. This reprefentation of your felf 111 j proceeds from hence, that all the rays, which flow from • all the points of your face to the looking-glafs, are reflec- ; ted in fuch a manner to your eye, as if they proceeded - from as many other points as there are in your face, equi- diftant from each other, and as far beyond the glafs, as ' r ou are of this fide of it ; and confequently you fee your • image at as great a diftance from the glafs, as you your felf are, and exaftly like you; and from the pleafure this ' beauteous reprefentation affords you, you eafily conceive what pleafure the original mull give to others. The ce- lebrated Milton has in his fublime poem finely defcribed the delight and lurprize of Eve the firft time Ihe lurveyed ! herfelf in a fountain, That Jlood unmov'd Pure as the expatfe of heav'n . And this image of herfelf appeared fo charming, that, like another Narciffus, Ihe afterwards ingenuoufly confef- fed to Adam, that though Ihe thought him fair, yet he feemed, -Iefs fair Lefs winning foft, Iefs amiable mild. Than that fnooth wat'ry image Does not this paffage of Milton convey fome malicious in- 84 DIALOGUE ll. finuation, faid the Marchionefs ? And is not his real mean* ing that the fight of a hulband gives a woman lefs plea* fure than even an image or a fhadow ? However, I agree : that our firft parent was in the right to admire this fine ' phenomenon, and I have been greatly to blame in my riegledt of it ; but we are too early accuftomed to the fight j of thefe things, for them to make a ftrong impreffion upon us. If any one had told me a few days ago, that certain rays, flowing from my face, would have been reflected from the looking-glafs, I fhould have believed it to be one of thofe ufual enigma’s which gallantry borrows from tradi- tion, or founded upon the authority of fome old romance, i But I coniefs that from this time, I lhall furvey myfelf in the glafs with a fort of philofophical pleafure. There is no greater pleafure, continued I, to philofo- phers, than that of obferving the various fportings of the rays of light, in palling through a gibbous glafs, or one that is convex on both fides, and from which its refem- blance to a grain of lentille , is termed a lens. And upon this depends the explanation of vifion. If two rays of light mutually parallel , that is to fay, which always keep the fame diftance from each other without approaching nearer j or removing farther oif, like the efpaliers of thefe walks, fall upon a lens , by means of that refraftion which they fuffer, they are united beyond it, into one point that is called the focus of the lens, which is more or lefs diftant in proportion as the lens is more or lefs convex. So that the greater the convexity, the lefs will be the diftance of the focus ; and the lefs the convexity is, the diflance of the focus will be the greater. And this diftance of the focus is what diftinguifhes the lens : as for inftance, we fay this lens has fo many feet of focus , aud another fo many, juli On Light aud Colours. 85 is we fay fuch a machine can raife the water to fuch a ■-t leight, by which we would fignify the force and adivity i pf it. I fancy, faid the Marchionefs, that the reafon why ; his point is called a focus, is becaufe a candle may be fet aij )n fire when placed there, as I once faw done by a perfon 5II ,vho undertook to light a candle without the help of fire :on iy the fun. He might fafely have engaged, anfwered I, a o light the candle not only without fire, but even with :a ce. For a lens made of ice in a little fpace of time pro- )f luces the fame effed: as one that is formed of glafs. How nany impertinences might this have furnilhed the poets :e, vith in that time when their language was, See guarded by the watchful powers of love , Fair Delia f umbers in the peaceful grove ; Struck with the fight , Jet world' ring mortals own, Amidft the gloomy foades , a radiant fun ! But the reafon that you give is a very good one : the burning which follows in that point where the lens unites die rays which were at firft parallel, and forms them into 1 flame, is the very reafon why it is called the focus. All :he rays, which are not mutually parallel, but in going r rom a point keep continually removing from each other, ind which are called diverging rays, unite beyond the lens ' .n another point, which is always more diftant than the ; r ocus of the lens itfelf. Hence we fay, that a convex lens : renders the parallel and diverging rays converging. For : thofe rays are called converging, which proceeding from various parts, have a tendency to unite themfelves in one point. Jult as the alleys of thofe woods which are formed in the fliape of liars, continually approach to one another till they all meet in the centre. Thefe walks, faid theMar- thionefs, interrupting me, might be called diverging, with 86 D I A L O G U E II. regard to one in the centre of the wood, from when* they proceed, always removing ftill farther from one an< ther. You only want, Madam, anfwered I, to turn ov< Euclid and Apollonius a little, and fometime put on a abftradted look, and you will be a complete geometr cian. But to follow the trad! of thefe rays as we have begu! the more that point, from which the diverging raj fet out, is diftant from the lens, the nearer the lens and it focus is that point where the rays unite ; and fo on th contrary, the nearer that point from whence the divergin; rays proceed is to the lens, the farther off from it and it focus is that point where they unite; provided however that the point from whence thefe rays proceed be not a fuch a diftance, that inftead of uniting they are thrown ou of the glafs either diverging or parallel. Opticians, in or der to find out the innumerable variations which thefe ray may form, make ufe of a certain fcience called Algebra which after having extended its empire over all the region: of natural philofophy, has fince by the ingenious contriv ance of intereft been appropriated to civil ufes, to deter mine the chances of thofe games which are.the moft fub jedt to the caprices of fortune, and has even infmuated it felf into the litigious provinces of law and morality. B] the help of this fcience, they have always certain letter at hand, called fymbols, connedted with each other bj certain figns : with thefe, provided they know the qualitj of the lens, that is. the diftance of its focus and of the point from whence the rays proceed which fall upon the lens } or the diftance of the point to which the rays tend if they fhould fall converging upon the lens, Opticians can tell you in a moment, whether the rays will unite or not, whe- On Light and Colours. 87 er they will go out of the lens diverging or parallel, and what point they will unite. This looks like a fpecies ‘ magic, which perhaps would not have efcaped unpu- ifhed in that age, when it was a crime to affert the motion 'the earth, and the exiftence of the Antipodes. The uniting of the rays diverging from feveral points, ;; to the like number of points beyond the lens, which n ems in itfelf a very indifferent thing, fupplies us with ne of the fineft fights you can poflibly imagine. If to hole made in the window -fhut of a darkened room, you ; pply a lens, and over-againft this at a proper diftance J iere be placed a fheet of white paper, you will fee all the - t bjedts which are without the window, efpecially thofe 'hich are diredtly oppofite to the lens, inverted and paint- fl upon the paper with a beauty, vivacity and foftnefs of . olours that would make a landfkip drawn by Claude Lor- ain, or a viflo by Canalleto, appear faint and languid, ou will perceive the difiance of the objedls exadlly the ime as you would do in a pidlure, that is, the fmalnefs of lofe objedls which are far off, from a little confufion and bfcuritv, from a certain faintnefs of the colours, and in tort, from a moft exact perspective the grand fecret of lat happy art of delufion, painting, which accompanies nd affifts all I have been defcribing. It is impoffible to sprefs to you the pleafure that refults from the motion nd life which animates this fine piece : the trees are really gitated by the wind, and their fliadow follows the motion. he flocks bound upon the lawns, the fnepherd really ralks, and the fun-beams play upon the waters. Nature raws her own pidlure inverted and in miniature. It is pity, faid the Marchionefs, that fo fine a pidlure rawa by the hand of fo excellent a mafter, fhould be turn* H 88 dialogue ir. ed upfide down, which I am as much at a lofs to find reafon of, as I am of the manner in which it is form Let us fuppofe, anfwered I, without fide of the wind over againft the lens an arrow to be placed horizontal that is, even with the bottom of the window : let the po of this arrow be on the right-hand, and the feathers on t left, Suppofe too that the extremity of the point em^ rays npon the lens w’hich entirely cover it. Thefe ra^ unite beyond the lens itfelf in another point, but in paffii through the lens, infiead of being on the right hand they were at firft, as proceeding from the point of the row which we fuppofed to be on the right-hand, thi' change their fituation, and are placed on the left. In tl fame manner the extreme point of the feathers throws ra J upon the lens which unite in another point, and after the paffage through the lens are turned from the left to tl right hand. Juft in the fame manner as if a perfon hel two fticks, one in each hand, and fhould crofs them tc gether; that which before the crofting was on the rigi will afterwards be on the left-hand, and on the contrary that which was on the left will be on the right. Not' the rays, that fall upon the lens, crofs each other, juft a thefe two fticks do in the point where they touch. Th fame may be faid, if the arrow lhould be fet upright Thofe rays which proceed from the top of it, after bein^ crofted and palling through the lens, remain at bottom and thofe which came from the bottom at top. Thui you fee the wftiole fituation of the rays is changed. Thai which was at top is placed at bottom, and what was at bottom appears at top. That on the right-hand is turned to the left, and that on the left to the right. If a fheet of paper be then placed behind the lens in the place where On Light and Colours. I 89 hefe rays unite, they will draw you an image of the arrow in finch the point fhall be on the left hand, and the feathers n the right, or in other words, the image will be the ^jeverfe of the objedh You may eafily transfer what I Jiave faid of the arrow, to a landfkip, a piazza, or any o- , Jher objedt, with this difference however, that all the parts ■I'f a landfkip or piazza cannot be equally diftindt in the •idlure as thofe of the arrow are, becaufe the rays unite j a -t different diftances from the lens, in proportion to the lifferent diftance of the points from whence they flow, f, for inftance, an objedt in the middle of this walk is feen liftindtly upon the pidlure, as it will be if the paper be fet n a place where the rays which come from it unite, thofe >bjedts which are nearer cannot be diftindl, becaufe the )oint where the rays unite is at a greater diftance ; neither jCviU thofe objedts which are farther off be diftindl:, becaufe Jhe point where their rays unite is nearer the lens, and J :onfequently the rays, as well of the one as the other, fall lpon the paper disjoined, and only form an image there vhich will be very dim and languid, or in other words, , :onfufed; fo that for thofe objedts which are far off, we nuft place the paper nearer the lens, and fet it at a greater j, liftance when we fhould fee thofe which are near. It will now be neceffary, faid the Marchionefs, that you hould provide your felf with a lens, and give me a fight )f thefe fine landfkips all round us upon a flieet of paper. ?or I muft confefs, I have a great curiofity for this, both is a woman, and as a woman whom you have rendered lalf .a philofopher. I wifh, anfwered I, that I had one vith me to fatisfy your curiofity this moment" which by vhatyou fay muft be extremely ftrong. But I will fatisfy fou as foon as I am able with a view of this ca?/iera obfcura • H 2 po DIALOGUE II. I But what will you imagine if I fay to you when we are ii ■.it, fnppofe yourfelf to be placed in one of your eyes, am : to fee every thing that paffes there ? x The camera obfcura reprefents the inlide of our eye which is nearly of the fhape of a ball: the hole in th window is the pupil which is in the fore-part of the eye and appears in all as a dark hole, fometimes greater, fome times lefs. The lens is the chryftalline humour which ii exactly of that figure, and is placed over-againft the pupil and fufpended by certain little fibres called the ciliar pro cedes, which proceeding from a coat or very thin fkin which incompafles the infide of the eye, are fixed in the edge of it: the paper on which the image of objedts is de pidtured, is the retina, compofed of the filaments and medullary fubftance of the optic nerve, which is fattened to the eye behind, and is the great channel of communi- cation between that and the brain. The fpaces which are between the fore-part of the eye and the chryftalline hu- mour, and between this and the retina, are filled with two humours lefs denfe than the chryftalline, but denfer than the air. By the help of all this apparatus, external ob- jedls are pidtured upon the retina in miniature juft as in the camera obfcura, and thus we fee. Really I did not think, faid the Marchionels, that I fhould be tranfported thus in an inftant from the camera obfcura, to the infide of my eye, nor that the fine pidlnre, you before defcribed, had fo much relation to vifion. Many muft have obferved this, anfwered I, before you, without fufpedling any fuch relation. If there be a hole made in any room which is otherwife dark, and this hole does not exceed a certain bignefs, this will be fufficient to _ V Ciew you thofe objedts which are over-againft the hole, n On Light and Colours. 91 painted upon the oppofite wall or the floor of the cham- ber. Is there no need of the lens then, faith the Marchio- lefs, in order to the produdiion of this picture ? It is ne- - . :elfary, anfwered I, to give it in fome meafure t£ie finithr : ng ftroke. But even without the lens if the hole be flnall - enough, and the oppofite wall or the floor not very dif- ant, the rays which pafs through the hole are near enough v iot to appear confufed, and may draw a tolerable pidture : '5 i>f the external objedts upon the wall or the floor. J If the chryftalline humour becomes opaque, which is - vhat forms a cataradt, there is no other remedy in this ■ afe to recover the fight, than by depreffing the chryftal- ■ [ne humour, and cutting away the fibres which hold it fufr ■ "ended, and then fome faint reprefentation of the objedts ray be drawn on the retina of thofe unhappy perl’ons. !ut as the pidture in the dark room is much weaker and aore confufed if there be not a lens applied to the hole, o is that which is made upon the retina of thefe perfons, then the chryftalline humour which is the lens of the eye ; no longer fixed over-againft the pupil. It is true, thofe wo humours which remain, the glaify and aqueous, help he rays to unite, and a convex glafs may in fome meafure apply the defedt of the chryftalline humour. It would i e well if this convex glafs could affift the eyes under a nuch more terrible diftemper, in which, though they feem veil and found, the retina or the optic nerve being weak- ed and obftrudted, cannot tranfmit any fenfation to the rain of the images of objedts, though they are clearly nd diftinctly drawn upon it. lhis diftemper, whicn is ailed a gutta Jenna, occafioned the blindnefs, if not of he Greek, at leaft of the Britifh Homer, which he inter- H 3 $2 DIALOGUE II. weaves in his poem among the beauties of Paradife Lof! the battles of angels, and the pregnant abyfs. This picture then of the camera obfcura, faid the Mat chionefs, which feemed of no other ufe than to implo idle people, or fuch as have a tafle for painting, is in rea Ihy of very great fervice to us, and in fome cafes even re {lores fight to the blind. Are we not obliged to Des Car tes for having rendered it fo ufeful.to us ? Des Cartes, an fwered I, is very happy, to whom you would willingly b obliged for every thing. But in this cafe your acknow legements are due to an induflrious German, who laid th foundation of many things which others have fince brough to perfection. He was the firft who gave us a true expli cation of Vifion, which has always been a fubjeff of fpe culation among philofophers ; and confequently has hac its lhare of ridiculous notions. For fome among the an cients fuppofed certain rays, which, extending themfelve; from the infide of the eye to its fuperficies, preifcd the aii as far as the objedl to be feen; and this air finding fome refinance from the objeft, made it perceptible to the fight; others affirmed that Vifion was formed by the reflexion oi the fight ; that is, becaufe rays flowed from the eye to the objedtj and were from thence reflected back to the eye ; fo that thefe gave it an exad information what the objedl was. Nor were there wanting fome who affirmed that certain effluvia go from the eye, and meeting in their way with other effluvia of bodies, they link themfelves with thefe, and turning back again with them to the eye, give the foul a perception of objedls. And the moft rational among them aflerted, that extremely fine membranes form- ed of particles and atoms are thrown off from the furfaces of bodies, and have mutually the fame difpofition an 1 On Light -and Colours. 93 )rder, as there is in the furfaces of the bodies themfelves from whence they proceed, and that thefe membranes, 1 which they call Jimulachra, or images exatftly refembling the bodies from whence they are fent, enter into the eye, and this is the caufe of our feeing. And it is furprifmg to 'think that in fuch an age as this, fuch a country as Eng- . land, there (hould be found any perfon * who, (hutting his r eyes againft the light of things, would be again immerfed in the profound darknefs of unintelligible ivords, and affert that Vifion is formed by means of the different degrees of the expanfive force communicated from bodies to the eye through a plenum, and that the different modifications of It, as clearnefs, weaknefs, and confufion in the fight, arife from the proportion which thefe expanfive forces have 1 with the contradile ones of the optic nerves. However, all the moderns except this, (who, like him that wrote in thefe latter ages againft the circulation of the blood, was neceffary to give us a fpecimen of the infinite varieties and extravagancies of the human mind,) have rejected thefe * Dr. Robert Green, fellow of Clare-hall, Cambridge, published in 1711. a bookintitled the principles of natural philofopby, in which is {hewn the infufficiency of the prefent fyftems to give us any juft account j of that fcience , and the neceffity there is of fame neiu principles in order to furnijh us -with a true and real know lege of nature. In this book he un- dertakes to {hew the unreafonablencfs of the greatefl part of that philolophy hitherto received under the name of the Corpufcularian, and then proceeds to lay down the principles upon which alone he thinks it poihble for nature to be explained. He farther endeavours to evince the incompetency of the prefent mathematics to furnifh us ! with any juft or adequate reafonings upon nature, and the neceffity there is of fome new principles in that fcience, which he has in fome manner explained in the geometria folidorum annexed to this book, and from which he has been long allured that the fquaring of the circle is not impoffible. The celebrated Mr. Cotes pro- ! feffof of aftronomy ufed to fay that this book {hewed the author to have bad as extraordinary a genius as Sir Ifaac Newton, fince it mud have been the effect of defign to guard fo effedhially as he did '• j againft faying any one right thing throughout fo large a treatife. 94 D I A L O G U E II. chimerical explications, the offspring of pride and Ignor- ance ; neither have they greatly eileemed the reafonings of thofe who thought that the effluvia proceeded rather from the eye, than from the objects; fince it was more reafonable they fhould proceed from an animate than an inanimate fubftance ; that the ears, the mouth, and the nofe, were made concave to take thefe effluvia in, whereas the eye was made convex, and therefore proper to fend them out. Notwithftanding all thefe fine reafons, optici- ans have reduced the eye to a perfeft camera obfcura, re- jecting and extinguiffling that light which the greater part of the ancients fuppofed to proceed from it. Indeed the auguft eyes of Tiberius mull perhaps be excepted, who, as it is faid, when he walked in the night, could for fome- time lee as well as in clear day light, which is faiu to arife from his emitting certain fparks from them. You may fay the fame thing of any other perlon, who is confidera- ble enough to deferve that an exception fliould be made in his favour. It will be neceffary for us, faid the Marchionefs, to look upon cats as confiderable perfons, and make an exception in their favour too. We lhall willingly grant them that honour, anfwered I, only they mull not take it ill if we fay that the light, which feems to proceed from their eyes in the dark, ferves only to give light to objeCls, and by this means the image may be drawn upon their retina: for Vifion, as well as innumerable other things, is performed in the fame manner in men as in brutes ; or rather we may acknowlege ourleives obliged to thofe for that evidence which we have of the manner oi its operation . for in or- der f o demonfirate it, we make ufe of the eye of an ox, or fome other animal, at the bottom of which when the On Light and Colours. 95 eoats are taken away, if we place a very thin and tran- fparent paper, we fhall fee the image of thofe objects, to which the eye is turned, drawn upon it and inverted, juft the fame as in a camera ohfcura. This fhews how very capricious our fenfes are. For inftance, we fay that there is heat in the fire no lefs than in our hands. Thus we confound one motion which is in the fire, and another that it raifes in our hands, with I the fenfation of heat, which fenfation is neither in the for- mer nor latter. But we do not fay that colour is in our I eye as it is in objects, though without difpute the colours raife fome vibration and motion upon the retina , and are painted upon it as ftrong and lively as they are upon the objedls themfelves. Thus we confound two things in the perception of heat, and only one in that of colours. It appears, faid the Marchionefs, that we are much obliged to our fenfes in this point, for exempting us from one illufion at leaft. But do not they amply repay them- felves by thofe many others to which they have fubjedted our fight ? We fee only one objedt, though it be looked at with both eyes, and fee it upright, though it be drawn inverted upon the eye. You are a little too much pre- judiced againft the fenfes, anfwered I, and I muft for this time undertake their defence. Is not the reafon of all this violence which you exprefs againft Vifion, becaufe you had not the explanation of it from Des Cartes ? De- fend it, ifyoupleafe, faidlhe, without accufing me, and refcue it, if you can, from the charge of thefe two illufion s which I allege againft it. Would they not rather be illu- lions, anfwered I, if we were to fee an objedt double which we know to be Angle, and that to be inverted which we 96 DIALOGUE !I, know to be direct ? To-morrow we will enter upon a di cuffion of thefe two points, which Huygens, one of tt great promoters of knowlege in the lafl: age, thought be! yond the reach of human underftanding. To-momr perhaps you may know more than that great man, but i is impoflible for that acquifition to render you more charm ing than you are to-day. Ul» SsM, [ 97 ] DIALOGUE III. ?veral particulars relating to Vifwn , difcoveries in Op- tics, and a confutation of the Cartefian fyftem. r H E Marchionefs felt the utmoft impatience to be more learned than Huygens. She was not for lof- ig a moment’s time, but would have continued our dif- Mirfes upon Vifion, the next morning as foon as ever we •ere up. I told her that we mull prepare ourfelves with nmewhat more ceremony for fo high a degree of know- :ge, and that it well deferved that we fhould at leaft wait 11 after dinner. In the interim not to lofe time, (he might :arn how it comes to pafs that the eye fees the obje&s r hich are without it, but cannot at all fee itfelf. And 'om hence fhe might form a clearer idea of certain ver- :s which no doubt mull have been often addreffed to Ser. This was all the optics fhe could get from me in the lorning. She waited for the afternoon with as much npatience, as an Initiate full of the expe&ation of being :t into fome profound myftery. In order to underhand ,-hy we fee only one objedl with two eyes, would you be leafed, Madam, faid I, if I fhould tell you that in reality ?e fee only with one eye, and that the other remains idle nd at reft? You had better, faid fhe, at once reduce us 3 a fingleeye, and then you will have no farther difficulty, fhould be as well pleafed, if you was to fay that we walk lily with one leg. You are more moderate, anfwered I, 98 dialogue iii. than the Latin poet, who fays, that women would bj ill pleafed to have but one lover, as but one eye. this ftiange explication however was given by a grave j lofopher, and refembles the pride of the Chinefe, v fancy that all nations except their own fee with but 1 i eye, fince both the one and the other are equally the <| spring of ignorance. But this may ferve to let you | what difficulties there are in folving the queftion we ; now upon. Another made the optic nerves to refemll two lutes compofed of various firings, which have an < adl correfpondence with each other, fo that the two ima^i of the objedt falling upon firings wound up to an eqcl height or a unifon, the objedt mufl appear fingle. But ;| thefe fine and ingenious explications will not make you better philofopher than Huygens. I believe that the tri explanation ©f this difficult phenomenon, like many othe in Vifion, depends upon experiments. The fenfes of fee! ing and fight lend each other a mutual affiflance in tl formation of our ideas, juft as our eyes and ears help ead other when we learn a new language. The fenfe of feel ing, which is much ftronger than the fight, has conftantl informed us that in the ordinary way of feeing, the objedt i but one, and by a long habitude we join the idea of on fingle objedt with the two fenfations of it. In the farm manner an objedt that is felt with two hands or two finger ■! at a time, notwithftanding the two fenfations which wecame fingle, and in time all the reft, though the diflo- :ation ftill continued. I may venture to affirm that, by nrtue of this experience, Argus with all his hundred eyes lid not fee the fine heifer committed to his charge by the ealous Juno, at all more multiplied than Polipheme did biis Galatea with only one eye. You feem to exult mightily, faid the Marchionefs, in this experience which we gain from our touch : will it give you confidence enough to undertake by its affiftance the folution of that queftion I propofed to you yefterday : How it comes to pafs, that obje&s, which are drawn inverted upon the eye, appear direct in the mind ? Thefe experi- ments, anfwered I, extend farther than you perhaps ima- gine, and the ideas of fight confidered with regard to thofe which we received from touch, are no more than four I 100 D I A L 0 G U E III. ftrokes of a pen compared to a fine relief. We have ; example of a ftatuary, who though he was blind, yet the help of his feeling made tolerable good likenefles : o of the greateft mathematicians in England, that land phenomena, and who could give you a much better < planation of optics than I can, was yet deprived of fight fo young, that he may be affirmed to have b< born blind. This perfon is certainly much moi'e wonde, ful than that learned Frenchman, who, without eith voice or ear, undertook to learn mufic, and very muc, improved the greatefi and moft curious myfteries in th; art. Feeling furnifhes the imagination of this great ph lofopher with much clearer and more diftinft ideas, tha others receive from fight. What a pleafure would h| have in making ufe of your fine fingers to explain the con verging and diverging of the rays ? On the other hand what could we learn, or what could we do without ou;| feeling ? We fhould be incapable to judge of the fituation diftance, or figure of objects, as Berkley had prophefied, who perhaps confidered the metaphyfics of Vifion more than any one ever did ; and experience has verified this in fome perfons, who, after being cured of cataracts born with them, could not form any judgment, till the touch lent them its affiftance ; without this, our eyes would con- tinually tantalize us with a view of knowlege and pleafure, which we could never enjoy. The daily experiments then, that we make with our feeling, inform us that objefts are dire£t, in the fame manner as they teach us they are fingle, that they are placed in certain fituations, at certain dif- tances, and of certain figures. I believe Des Cartes is the only one who ever pretended to give an immediate expli- cation of this difficult phenomenon by a fimilitude. Sup- 101 On Light and Colours. fe yourfelf, faid he, to have two fticks acrofs each other, e in your right, and the other in the left hand, and to ilk with your eyes fhut about a room with thefe fticks fore you. There is no queftion but you will think thofe mgs which you touch with the ftick in your right-hand, .d which by this means will make a prelfure upon that nd, to be on the left ; and in like manner whatever you ' |uch with the other ftick in-tfee left-hand, you will affirm be on the right. After the fame manner the rays w'hich J oceed from obje&s to the bottom of the eye, crofting ch other in the chryftalline humour, thofe which prefs le retina on the right fide will make you refer thofe points - Dm whence they proceed to the left fide, and thofe rays ‘ %hich prefs it on the left you will refer to the right fide ; a |d thus thofe rays, which prefs upon the upper parts of ■ le retina , will make you refer the points from whence •ley proceed to the lower part, and thofe of the lower to le upper. And by this means the image, which is in- irted upon the retina , makes you fee the obje&s direct. Indeed, faid the Marchionefs, this is very ingenious; I tiy may not we confine ourfelves to this without feeking y other, fince it gives us an immediate explication of ir phenomenon ? Experience, anfwered I, unhappily forms us, that this is not an ingenious explication : a ..by who ftands upon his head fees every thing inverted, I itwith (landing the images of external objects are pictured >on his retina , in the very fame manner when he is in is fituation as they are when , he ftands upon his feet, e has no other idea of high and low, than what regards s own fituation ; and when he is in this inverted pofiti- i, he imagines the whole univerfe to be fo too. Befides, te explication of Des Cartes fuppofes the idea of hi^h i ° I 2 102 DIALOGUE Hi. and low, right and left, which, we can only have fro feeling, to be antecedent. | It is our feeling, which by an experiment every mome 1 repeated has conftantly taught us to call the . earth, t| wards which we find ourfelves continually carried by gt vity, low, thofe things which are contiguous to the eart as the pedeftal of a pillar or our feet, below; and tin things which are diftant from the earth, above; as o head or the top of a tree. The fenfe of feeling conve thefe and the like ideas into the foul of a man born blic with as much exadtnefs as that of fight does the ideas colour into ours. Now, if we fuppofe that vail whi hides the vifible world from his fight, to be taken aw ail at once, and confider in what manner he would jud of the fituations of obje&s, we might from thence arrive a dear knowlege of the manner in which we ourfelves jud of them, fince we have the ideas of high and low in coi mon with him : he would certainly be more furprifed firft opening his eyes, than the famous * Epimenides w after his long fleep of fo many years, who remember nothing which he faw about him when he walked, n even the place where he had been born and brought u A new fcene of ideas difplays itfelf to him, a torrent new perceptions rufii upon him through this new aven by which obje&s enter the foul. Amazed and overwheli * A Cretan philofopher, when he was a boy, being fent by 1 father into the country, to fetch a fhec-p, he turned out of the ro at noon, and repofed himfelf in a cave, where he dept s 7 years. . J ter this refrefliment he awaked and looked about for the flieep, in gining he had dept but a little while; not finding it, he proceed to his 3 father’s country eflate, where he faw every thing altered a. in podelTion of another. He then returned to the city, and wt to his father’s houfe, where his younger brother, now grown an c man at laft knew him, and gave him an account of all that h happened. He was held in great veneration among the Greel who imagined him a peculiar favourite of heaven. He is faid to ha lived till i jo years old, or, according to others, ip 7 . On Light and Colours. 103 d with them, he finds himfelf tranfjported, without know- lg how, into another world. What a pleafure, what n extafy muft this be, faid the Marchionefs ! If novelty i'hich always hovers about thefe things of which we have n idea, and is nothing more than an. unufual combination ;f thofe objeCts we are already acquainted with, affords b much delight, what an infinitely greater pleafnre muft his man have in a world of things really new, and a new ombinations of thofe ideas which he before had joined ;0 thofe, with which the addition of another fenfe abun- lantly fupplies him. But as human happinefs is too often ittended with fome alloy, is it not poffible for him to fee omething that would make him wifh his eyes {hut again hen they were hardly open ? He would have great rea- on to believe, that thofe objects would appear pleafing o this new fenfe, which had been fo to the reft, and flat- i;||:er this as agreeably as they had done thofe. But might liaot the event happen quite contrary to his expectation ? . tnd thofe objeCts, which had delighted his touch and hear tog, prove very difagreeable to his fight ? So that infteajl of increafing the number of his pheafures, this new fenfe iivould deprive him of the moil fenfible of them, and per- haps cruelly diffolve fome pleafing tye which the others had clofely bound. It is true, anfwered I, that thefe fenfes do not always agree : how many perfons do we daily fee, who, convinced by forrowfnl experience, that the reality of things does not agree with their outward appearance, find themfelves too foon in poffeffion of what they once thought they could never obtain foon enough ? A blind man, anfwered the Marchionefs, at leaft, while he is in love, Ihould never defire to fee ; fatisfied in the judgment of thofe fenfes which I 3 104 DIALOGUE III. reprefent an object agreeable to him, why fhould he 1 that of another, which perhaps would at once conde his choice, and, like reafon, probably make him fee||i misfortune without giving him any affiftance to avoid) The only confolation, anfwered I, that this miferable } fon could have under the misfortune of fight is, that! would not be unhappy fo foon as you perhaps imagi How ! faid fhe, if the joy of receiving his fight did | entirely deprive him of all complaifance, would not very firft thing he defired to fee be that perfon for wh fake he principally wifiied for the fight of his eyes? A •when he had feen her, he would immediately, if fhe fhoi appear difagreeable, perceive his unhappinefs, if with | gard to beauty, love did not render him a fecond till blind. He would enquire for her, anfwered I, would ! her, and yet would not by that means know her aga This would be a miracle even beyond the power of love effeft • he would hear, if you will, the found of thofe woi pleafing to his ear, and ftill more pleafing to his heai but he would not know the mouth from whence they pr ceeded. Yet more, he would be fo far from diftinguifhii] another, that he would not diftinguifh himfelf, his owl feet or hands, from any affiftance his new fight coui give him, fince he mult be utterly ignorant of the coi r.exions which the perceptions of fight have with thofe < the touch ; yet this connexion is ubfolutely necelfary in ordi for his knowing thofe objedts again of which he had no ides but what he received from fenfes of a nature very differer from that of fight, and depends upon an experiment whic he has never yet made. His own hands would be the fir objea he would learn to diftinguifh, by touching and loof ing upon them at the fame time, and remembering ths On Light and Colours. 105 ich an idea of his feeling would agree with fuch another ief his fight. When he had learnt this fhort leflon, love rould the more eafily conduit him to thofe experiments hat would foon, either to his joy or forrow, fatisfy his cu- piofity, and we will conduit him to thofe that may content urs, which is of a more philofophical nature. One of the firft he would try, would be to lift up that and which he has now no trouble to diftinguifh, and in oing this, he would perceive fome change in the fituation not-i 1 hvhich he received of it from his fight, and the reafon of A his change is becaufe the image changes its fituation in the (lot etina, in proportion as the hand is higher or lower. Guid- artd by nature herfelf, he would diligently obferve what ;irort of fenfation he felt when he held his hand up, and .1 (whenever he felt the fame fenfation raifed in him, either by aii he fame or any other objedts whofe image would fall in the ove ame fituation of the retina, though unknown to him, he V or siould conclude that objedt to be high, or in that fituation hearlti which his hand at firft was. By this means connedting ,'Jhe old ideas of feeling, with the new ones of fight, he Stodges of the height or lownefs of the objedt, of its being e iirect or inverted ; and it is of no importance, whether the :oul :nage of this objedt be pictured upon the retina , diredt, or ^averted, or in any other pofition. i,' e l External objedts zvtfignifed to him, if I may ufe that ex- T( j|)reffion, by certain fenfations of light and colours, as the thoughts of the foul are to us by certain charadters, not by Jjirtue of any refemblance between the one and the other, hiJmt by means of an arbitrary, yet conftant and perpetual. Si onnexion which we have obferved between them. And -i| is when we are accuftomed to any particular manner of ii writing, it makes no change in the order of the ideas which 106 DIALOGUE III. thefe charadters excite in us, whether they be written fror left to right, as ours are,, from right to left like the Oriental or from top to bottom after the Chinefe manner; fo whe ther certain images be drawn diredt or inverted upon th retina , it does not at all change our judgment of their fitu ation. The blind perfon, who has hitherto fafely conduced u through this labyrinth, refembles each of us. We en ter into light with our eyes lhut, and probably do no. begin to fee till we have for fometime felt. Thus, Madam you are indebted to the predominant fenfe of feeling for this new explication too, and however little you may imagine it, you will find that to this you have had the greateft obligations through the whole courfe of your life. I fee very plainly, faid fhe, that you intereft yourfelf for the honour of the touch, much more than for that of Des Cartes; and it is not poffible to propofe any difficulty but you will be ready to give it a folution by the help of this fenfe. There are other difficulties, anfwered I, which I will give you a folution of without this, that you may fee I have great plenty of explications. One of thefe perhaps may be to know what change muft be made in the eye, in order for it to have a diftindt view of objedts placed at different diftauces. For as in the camera olfcura, the rays which flow from objedts that are near unite at a greater diftance from the lens, than the rays of thofe which are more remote ; fo the very fame thing happens in the eye, where the rays, which pro- ceed from the pillars of this gallery, unite at a greater dif- tance from the chryftaline humour, than thofe that come from thefe trees which are farther from it : what ch mge then muft be made in the eye, in order that when we look On Light and Colours. 10? upon thefe trees, after having looked upon the pillars, the rays which proceed from them may be united upon the retina , or in other words, that we may have a diftindt view of them ? The retina, anfwered fhe, mud be brought ■ nearer the chryftalline humour, juft as the paper in the camera obfcura is brought nearer the lens, in order to give us a diftindt image of the more remote objedts. You have hit upon the true explanation, anfwered I; j ! and fome have affirmed, that certain mufcles, which in- : compafs the eye, are made ufe of to produce this effedt, and prefs the retina farther back from the chryftalline hu- • mour, or bring it more forward, as different occafions require. Thefe mufcles have befides another office, and help us to lift up or deprefs the eye, to turn it to the right or left, and give it a certain oblique motion which Venus 1 has the principal care of regulating. Others have fup- pofed that the retina remains immoveable, and that the chryftalline humour approaches nearer to it, and removes farther off, or that the chryftaline humour only changes its figure, growing more convex for near objedts, and lefs fo, for thofe which are diftant ; and others have affirmed, that each of thefe happens at the fame time, which will produce the fame effedt, as if the retina approached to or receded from the chryftaline humour ; but you had better fuppofe this latter, becaufe it is eafieft to imagine. For every diftance then, there is required a new conformation in the eye, and becaufe this cannot be effedted without motion, and a certain effort, fome are of opinion that the eye informs us of the various diftances of objedts by a certain natural geometry. But this way of judging, efpe- cially where very diftant objedts are concerned, is extremely Io8 DIALOGUE III. uncertain, as indeed almoft aO the reft are which hav< ever appeared upon the ftage of philofophy. But however this be, there are fome perfons who can- not bring their retina fo near to the chryftaline humour ns is necefTary, in order to give them a diftindt view of dif- tant objects. There are others, who, on the contrary,) cannot prefs it back far enough, to make objedts which are near appear diftindt. The firft of thefe, who are vul- garly called Ihort-fighted, are by opticians named myopes, and the fecond, commonly called long-fighted, presbyta : \ thefe may be confidered as the extremes betwixt which that fight, which is called juft and perfedt, ftands. Not- withftanding the honour of being diftinguifhed by names drawn from Greek, thefe perl'ons could not help perceiving they had a defedt in their eyes, which led them to feek for fome remedy : the myopes in order to have a diftindt view of diftant objedts, and the preslytx of thofe at hand, Thefe laft found relief in convex-glafles, which, applied to the eyes, removed their defedt ; for thefe makingthofe rays to become converging, which would without their affift* ance have fallen diverging upon the chryftalline humour, unite them at a lefs diftance than they would otheiwife have done ; and the image of thofe objedts which are op- pofite to the lens, is drawn diftindtly upon the retina. The ?7iyopes found their remedy in concave glades which difperfe the rays and make them diverge ; contrary to the convex ones, which make the diverging rays become con- verging. Thefe concave-glades then give adifpofition to the rays, as if they came from a nearer objedt than they really do, and applied to the eye of a myope, they in a cer- tain manner tranfport the diftant objedt to a nearer fitua- tion, and thus a diftindt image of it is drawn upon his re- On Light and Colours. 109 tina ; for there Is nothing more required to give Ihort- fighted perfons a diftindt view of any thing, than, to bring it nearer to their eye. It was very happy for them, replied fhe, to find thefe ' jlafies as fafe and eafy a remedy perhaps as ever the art )f phyfic itfeif invented. But what did they do before hey were found out ? Till the thirteenth century, anfwer. d I, when thefe glafles are fuppofed to be invented, the dyopes were obliged to approach near to diftant objedts in 'rder to fee them diftindtly, hoping perhaps that an ad- , anced age, when according to the common opinion the etina approaches nearer to the chryftalline humour, might ive them fome relief from this inconvenience ; but indeed bis is a remedy much worfe than the difeafe. The Pref- ? ytae, on the other hand, were obliged to remove a great fay off, without any hope of ever feeing the objedts fitu- tednear them diftindtly, if they fhould at any time have a triofity for it, and they continually tormented their eyes ith plaillers and coilyria , without gaining the leaft ad- intage to their fight. I think the condition of thefe laft, id the Marchionefs, much more to be pitied than that te fir ft, both becaufe they cannot flatter themfelves wfith e leaft hope of growing better, and becaufe they lofe a •eat deal more in the converfation of ladies than the My- >es do. How miferable muft have been the ftate of a fjior Prefbyta, who could never have a diftindt view of his .iftrefs, unlefs he breathed his fighs ten foot diftant from .r ! Thefe are not fo much to be pitied, anfwered I, as you i agine, fince this defedt generally happens in an age when Ipe and the converfation of ladies naturally defert us. Ir this is a defedt of old men, as the very word Prelbyta no DIALOGUE III. imports. But there are other defedts and infirmities of tl fight incident to all ages, which are never placed in tl number of defedts, for the very fame reafon that the fol of being more folicitous for the future than the prefen and by that means continually procraftinating our happ nefs, is never reckoned among the lift of follies, namel becaufe it is common and univerfal. Philofophers, wl! have a quicker perception of things, have difcovered ar fought remedies for thefe defedts; one of which is, th very fmall objedts are inviftble, however near they may 1, placed to the eye; the other, that very diftant objedts caij not be difcerned, even if they are of a very great magn tude. Thefe are inconveniences which you fee are not all felt by the vulgar, but referved for the curioftty ar. nice perception of philofophers. The reafon of both di fedts is, becaufe the image of very fmall or very diftant ol jedts, painted upon the retina, is not big enough to l perceived by the eye, notwithftanding the proximity of tl one, or extraordinary magnitude of the other. The r medies invented by philofophers to fupply them are certa: inftruments, whofe only bufinefs is to magnify this imaj and render it perceptible to the eye, by means of vario ! combinations of glalfes, or by one alone. Thofe whit are made ufe of to difcern diftant objedts, are called tele, copes, and thofe which help us to a fight of exceeding fmf objedts, niicrofcopes. We are obliged to each of thefe ft an infinite number of difcoveries, which could never hai been made without them. The heavens are the princip; objedt of the telefcope, from whence it hasfurnifhed phi I of phers with more curiofities than ever Columbus could brin from America to enrich the cabinets of the naturalift For not to fpeak of the hills and vallies which they ha' Ill On Light and Colours. .(covered in the moon, the fatellities of Jupiter fo very i ;ful to geography, thofe of Saturn with his ring, it is to i ofe telefcopes that we owe our difcovery of the fpots in the .■ : n, Jupiter, and Mars, which are necefiary in order to Jtermine the periods of their/evolution round themfelves, 4d by the affiftance of thefe, aftronomers have given us J: exa£t a map of Venus, that they are as well acquainted pJith her mountains in heaven, as the geographers are , Jtith thofe upon earth. They have difcovered that this ■ ( anet has an increafe and decreafe, that it is at one time, df, at another full, in fhort, that its appearance and Jhafes exactly referable thofe of the moon, as it had been - pnjectured by the celebrated Copernicus, before the in- • jjmtion of the telefcope. Thefe give the celeftial bodies •jlieir proper diftances, and have {hewn us an infinite num- br of ftars, unknown to the antients, difcoveringfo great t 0 j quantity in the milky-way, 'as is fufficient to fupply ten r twelve worlds befides our own. In ihort they have iven us a true fyftem of our world, by extending its con- . nes to infinity ; fo that if a poet, to flatter a nation which i ad made a greater progrefs in the conqueft of the world, - pan in the knowlege of its frame, could fay, that when iupiter turned his eyes upon our earth, he could fee no- hing in it that was not fubjefi to the Roman empire, we nay affirm with greater truth, that if he looked upon the , leavens, or at lead the folar vortex, he could not fee any hing in it, but what is the difcovery and conqueft of the elefcope. You reprefent thefe telefcopes to me, replied the Mar- hionefs, under fuch fublime images, that I am afraid the nicrofcopes will make but a very infignificant figure, when ompared to them. There is, anfwered I, a very remark- K I 12 DIALOGUE III. able difference between them, in which I believe the have the advantage. The telefcopes, it is true, by covering to us the hills and valleys in the planets, their lions, revolutions round their own axis, that is to fay, tl day and night, the moons that from time to time fup the abfence of the fun; in fhort, by repreienting then be of the fame nature as our earth, have furnifhed us w materials to people thefe vaft and immenl'e bodies wh were before uninhabited, flood negledted in a corner the univerfe, and were believed to exift for no other t than to pleafe our eyes. But microfcopes have made us; reality fee an infinite number of animals, of which we b not the leaft knowlege before, in things which were i looked upon as very proper to afford them a habitatic Not to fay any thing of the difeoveries in anatomy and 1; tural hiftory, which we owe to thefe glaffes ; aromatic i fufions, a drop of vinegar, are peopled by fo prodigies a number of little animals, that Switzerland and Chi. would appear empty and uninhabited, when compared 1 them. Thejmicrofcope, faid llie, is the compafs of ph lofophy ; each of thefe have given their alhftance to tl | difcovery of new worlds ; the only difference is, that tl microfcope has lent its art to people, and the compafs l deftroy. It is very wonderful, anfwered I, into what innumerab animal worlds philofophers have penetrated, under tl: guidance of this compafs. It is an amazing thing to r« fiedt upon the rninutenefs, art, and curiofity of the joints bones, mufcles, tendons, and nerves neceffary to perforr the fwift motions of the fmalleft microfcopical animals. Thefe difeoveries fhe\v us in how little a compafs all ai and curiofity may be comprized, even in a body lefs tha On Light and Colours. i i 3 ..'mall grain of land, and yet as complete, as exquifitely r'med, and as finely adorned, as that of the larged ani- il. Their multiplicity is no lefs furprifing than their treme fmalnels. A drop of the green fcum upon water, > bigger than a pin’s head, will contain no fewer than t hundred ; which, far from being confined in that narrow tent, play about in it with all the freedom imaginable. ■ he eye of a butter-fly will contain more than twenty -four ■ dllions ofeyes ; and the wonder is dill greater, when we come ■ confider the organization of their fine aiid minute p3.ri.s. : the eye of a fly, which feems to be a little misformed ■otuberance, be looked on thro’ a microfcope, it appears ' be only a compofition of thoufands of little eyes, juft as 'me nubilous dars, on being viewed with a telefcope, ap- ear to be a cinder of innumerable [other liars. In fome ifedfs there have been counted no lefs than thirty four loufand of thefe little eyes, which, notwithdanding their ctreme fmalnefs, had each of them a chrydalline humour ; perfect as ours. Why are not our eyes, faid the Marchionefs, of fo fine textufe ? This quedion, faid I, Iras been already an- 1 vered. 1 For this plain reafoti , man is not a fly. i, Say to what ufle were finer optics given ? To inflpecl a mite, not comprehend the heav'n. But in fadt, there are fome infedts, that with thefe mi- rofcopic eyes can fee as far as the greated part of men. The bees, an indudrious fpecies of flies, from whofe labour ve reap fo great an advantage, can diredt themfelves fafely o their hives, though at a mile didance, when they re- urn laden with the fweet treafures of the fpring. It ap- )ears that what nature has given us in reafon, fhe has de- li 2 ' 1X4 DIALOGUE III. nied us in exquihtenels of fenfe. Pigeons, the couri ; of the eafl, fuch as that which brought news from Eg ) « to Jerufalem, when it was befieged, of a quick and powi ful fuccour, or that beautiful one prefented by Venus j Anacreon in exchange for one of his odes, and whic for having fo often carried his letters to Bathyllus, deferv to deep, and be fungupon that lyre which could refoui 1 ] nothing but love ; thefe flying couriers, I fay, being 1 ioofe by the perfon, who has a mind to fend home ne 1 of himfelf, afcend a prodigious height, and from thenc 1 ; though at a very great diftance, can fee their native cou try, and fafely diredl their flight to it, without the he of either flars or compafs. Moles feem to be quite coi trary to thefe fharp-fighted couriers. Nature, faid tl Marcliionefs, has perhaps made them amends fome othi way. It is probable, that fhe has conftituted the cond tion of animals pretty near as equal as that of men. Thei eyes, anfwered I, are certainly not to be envied : they ar fo fmall, and covered with hair, that it feems as if natur had given thefe tenants of darknefs, eyes to fee the light for no other end than to fly from it. Thefe animals ar not formed to contemplate the wonders of the microfcope nor fee in one drop of water fo many thoufands of animals : organized w’ith that exa&nefs which is neceflary to enabl* them to fee, move, andnourifh both themfelves and othes little animals, which repay them the mifchief they do tc us, and to contain within them an infinite number of lliU other little animals of their own fpecies, much lefs than they, and which only wait to unfold themfelves to make their appearance in the microfcope Thefe obfervations open a fcene of innumerable other worlds of animals un- known before, which, notwithftanding their extreme and On Light and Colours, 115 urprizing fmalnefs, have their greater and lefs, their ele- i F jt >hants and ants, juft as ours has; the only difference is, poi hat our ants become elephants when compared with their emu iirgeft animals, or rather are as the immenfe diftance of whi laturn from us, is to the extent of a grain of fand, elan Indeed, faid the Marchionefs, this new fcene of pigmy gives me as much pleafure, as that other immenfe ingi nd gigantic fcene of vortices , or funs diffufed over the :r,e thole univerfe. The little has its beauties as well as the ks ;reat, or rather, anfwered I, there is no great or little, ut with regard to ourfelves. Gulliver, who could deftroy :j]j he Liliputians like fo many flies, was among the Brob- : inagians kept in a cage like a Canary bird, or for an or- ament upon the chimney, like a Chinefe pagod. it is otli rincipally the microfcope, and that infinite number of :onJ 'gmy worlds difcovered by it, which has rectified our Tlj ieas of great and little fo much, that I am perfnaded, hat the confideration of this incredible and furprifing r . mallnefs, which it has rendered perceptible to our fenfes, „as ferved to foften and familiarize to mankind another onfideration which is the mafter-piece of human under- cc , : landing, and direflly leads us to the fubvernon of great nd fmall. This is the confideration of infinitely finall u uantities, which has made fo great a noife in the learned ^ rorld, and which you perhaps may have heard of. The : meaning of this expreffion is, that there are parts and uantities in extcnfion, fo exceedingly fmall. that they may e reckoned as nothing when compared with our meafures, s the fathom, foot, inch, and the like. So that if one f thefe quantities was added to the extremity of a line, ar example, of a foot, it would not increafe the Jen gih of ’• c, nor decreafe it if it was to be taken away. And \h$ K 1 1 6 DIALOGUE III. mathematicians affirm, that in thefe quantities, infinite! Wll with regard to the ordinary meafures called difr rences, there are innumerable orders and gradations, | that a quantity, which is infinitely ftnall compared wit the order of our common meafures, is infinitely gre; ■when compared with an inferior order of infinitely fma quantities, and fo of the reft. The moft enormous fize we have may become infinitely fmall when compared wit an order of greatnefs infinitely fuperior. To how fma a fize is reduced the coloftus of Nero, or that of Rhode; when compared to mount Athos, carved in the fhape of man, and holding a city in one hand, and pouring out river in the other ? Compared to Milton’s Satan, Virgil 1 Fame, the formidable Shade of * Camoens, that Polephem of the ocean, which appeared to the Portuguefe failors, hii its head in the clouds, and its feet in the unfathomable abyl of the fea ; or in fhort, what would all this appear to tha angel feen by Mahomet in his myfterious night, whof eyes were feventy thoufand days journey diftant from each other? It is computed that if he were of a human fhape '•here muft be the diftance oj^forty thoufand years journey ^g-^^irom his head to his feet. _ ^ Probably, faid the Marchionefs, there muft be a grea; number of telefcopes and fpeaking-trumpets in the Turkift paradife, in order for the Mahometans to be able to fe< and convene with thefe diabolically great angels of theirs r * Camoens, the famous Portuguefe poet, in his Lufiada, the full jedl of which is the ilifcovery of the Eaft Indies by his countrymen, conducts their fleet round the coaft of Africa, and as it fails in figjil of the Cape of Good Hope, he introduces a formidable fpedtre walk' ing in the depth of the fea, its head reaching to the clouds, its armf extended over the waves, and its whole form furrounded with clouds, florms, winds, thunders, and lightenings. This fpectre is the guar- dian of that foreign ocean which no flrip had ever pafled through be- fore, complains of his being obliged to fubmit to fate, and the bold undertakings of the Portuguefe, and foretels them the misfortunes 'hey muft undergo in the Indies. On Light and Colours. li 7 There are, anfwered I, the fame orders of infinites in die fucceffion of time, as there are in extenfion. An hour, i minute, a fecond, are of an infinite duration compared with periods of time infinitely Ihorter. How enormous muft the duration of the Roman empire feem to an animal, i which in the fpace of five or fix hours is born, grows up, produces one like itfelf, becomes old, and dies ? What we fhould call the flight of time, would feem to this infedt an eternity. But what are thefe durations of empires, . this long fucceffion of kings, emperors, confuls, and thefe ■ litedious fieges, when compared with eternity ? Is it more n than a point in which we live, fight, raife fuch great com- i jmotions, and make fo much noife ? The Orientals fay, ■there is a god that governs this world, who dies at the end d of a hundred thoufand years, and this fpace another fu- iperior God efleems but as a minute. And yet all thefe ' examples give us but a very imperfedt idea of infinity. This 1 confideration, the utmoft flxetch of the human mind, which ; we owe to Sir Ifaac Newton, and which entirely overthrows || all the ideas of abfolutely great or little, was the founda- I ition of the famous arithmetic of fluxions , or infinitely fmall | quantities, which tranfplanted geometry into a province entirely new. Here it made fo rapid and great a progreft, that all it had done before feems nothing, and here by the Jiaffiftnnceof new difcoveries it produced fuch ftrange para, doxes, that they have in fome meafure clothed truth in the agreeably furprizing drefs of fiction : and what is the moft remarkable in the new geometry is, that by confider- ing the properties, relations, and habitudes between in- finitely fmall quantities, it arrives at the difcovery of com- mon and finite meafures, which are the objedt of our en- quiries. 1 1 8 D I A L O G U E III. If the fagacity which we fo much admire, faid (he, con- fids principally in uniting thofe things in the mind, and finding their relation, which feem to be in their own na- ture disjoined and feparated, what an unlimited under- funding mufl Sir Ifaac Newton have had to find the rela- tion, and in fome meafure unite thefe quantities, disjoined and feparated from each other by the immenfe tradts of infinity, where the human imagination quite lofes itfelf! And, continued I, the confideration of thefe infinitely fmall quantities that we neither fee, nor can conceive, which appeared only fit to perplex geometry, have in fail fervcd to render it more eafy, and reduced it at the fame time to fuch general rules, that the mof fublime and abfirufe truths, in this fcience, are at prefent nothing but one of the infinite confequences which is loft among the croud of thofe that are deduced from the ftroke of a pen ; and, if you pleafe, in a circle of ladies ; truths that once required an Archimedes, with all that attention of thought which was neceflary to make a perfon infenfible of the noife of a town taken by form, and be knocked on the head with out perceiving it. This confideration then of infinitely fmall quantities, faid the Marchionefs, and the obfervations of the micro- fcope, which have rendered it more familiar and common, have given a very ftrange turn to geometry. It now treats of quantities, which from their extreme fmalnefs were once utterly unknown, and does not at prefent difdain to enter into the company of ladies. A province with which I be- lieve it was once as little acquainted, as with that of the infinitely fmall quantities. It is true, anfwered I, that geometry is rendered fo very familiar, as fometimes to fuf- fer itfelf to be treated by a hand as beauteous as that of On Light and Colours. 119 Venus of Medicis. But it is true likewife, that it fometimes refumes its fierce and favage difpofition, efpecially -when it is attended by that train of confequences, deduced from the broke of a pen, as I before mentioned to you, and goes back into folitude and retirement. Mankind however, faid fhe, ought to think themfelves greatly obliged to the microfcope, for having contributed to foften and familiarize a thing whole very name alone in- spired fo much terror. Mankind, anfwered I, are not . I very often guilty of the fin of gratitude, and, as that po- lite philofopher, who is to inftruCt you in the motion of the earth, obferves, there are fome who makemo fcfuple I to treat the ftudy of anatomy, which perhaps may have faved their lives, as a ufelefs thing. You may judge from hence, whether it be probable that mankind will be grate- ful at the expense of fo much confederation as is neceffary in order to know whether the microfcopes have contributed any thing to familiarize the calculation of infinitely fmall quantities, what this calculation is., and what ufes it may have ; all which things are neceffary to form a well-ground- I ed and rational gratitude. An Engjilh frier, called Roger Bacon, who lived in the thirteenth century, and had a general knowlege of the effect of the rtfrattions of light by a lens , and was befides acquainted with many other things which are commonly believed to be the production of much latter ages, fuch as the invention of gun-powder, the reformation neceffary to the calendar, and was fenfible of the falfe method of ftudy at that time in fafhion ; this very man, worthy of a ftatue and immortal honours, was ill treated, perfecuted, kept prifoner for many years, ac- cufed as a conjurer and wizard, and of holding intelligence with the Devil, in order to effect what required only fu- 120 D I A L 0 G U E lit. perior parts, and a free ufe of reafon ; and all the honouj thefe inventions, which we at prefent fo greatly admire, met with at that time was, that the inventor was judged worthy to be burnt alive. It is true, that at prefent the learned cannot admire the depth of underftanding, and the quick penetration of a man, who, in fo barbarous an age as the thirteenth century, thought in a manner that very few of his fpecies do even in this, age, as enlightened as it is. But what gratitude is this to perfecute, imprifon, and almoft burn him when living, and at the end of five centuries, to republifh and give him the higheft encomi- ums ? Is not this like deifying Homer after his death, when he had been fuffered to ftarve with hunger, while living ? The telefcopes, which have been the caufe of fo many fine difcoveries in the heavens by their afliftance, did not by that means at all advance his fortune here upon earth. It is furprifing, faid the Marchionefs, to fee the folly ; and caprice of mankind. In fome cafes they are fo ex- tremely fond of novelty, as to adopt the moft extravagant things merely on that account. This, we fee, happens, every day in the fafhion of drefs, fitting, taking fnuff, and even fneezing. At another time, novelty is an obje&ion to the moft ufeful and weli contrived fchemes. Are our judgments never to be guided by reafon ? The wife men of paft ages, anfwered I, appear to us like the moon juft on the edge of the horizon, and thofe of the prefent time, like the fame planet, when it is a ' great way above it. The image of the moon painted on ! our retina , when fhe is at the horizon, is lefs than when {he is elevated a great way above it, at the meridian, for example ; and this is occaftoned by the diftance of the moon from us, which is greater in the firft cafe than the fecond. 121 On Light and Colours. Yee notwithftanding this, we imagine her to be much big- ! ger at the horizon than at the meridian. This miftake proceeds from the interpofition of other objedts, as trees, houfes, tradts of land, fea and Iky, which are betwixt u* and the moon, when at the horizon, but not when fhe is ] at the meridian, for in that fituation fhe is left entirely to herfelf. Now as the objedts placed betwixt us and the moon, make us imagine that fhe is more diftant from us at the horizon, than the meridian, they are the reafons too why we imagine her to be bigger, becaufe the apparent bignefs of an objedt depends on the fize of its image on ;; the retina, joined to the judgment we form of its diftance; ■ ! Ifo that the image being always of the feme fize, the objedt mult appear fo much the greater, as.it is judged to be more ! liftant. Hence it is,, that adtoits, when they come from the aottom of the theatre, appear to us like, giants, the per. pedtive and the delufionof the feene making them ap- aear a great way off. Why fhould thofe objedts placed i ietwixt us, and the moon when at the horizon, feid the Vlarchionefs, interrupting me, make us imagine her to be arther off from us, than when fhe is at the meridian ? I hould think they would rather make her feem nearer, for n that fituation fhe appears to touch them, and it feems irobable fhe fhould appear at the feme diftance from us as he objedts themfelves: whereas at a greater altitude, we ee her placed in the Iky, and confequently judge her to >e at a great diftanee. We know, anfwered I, that the noon in both cafes is in the heavens, or rather that the leavens themfelves are an immeufe vault, to which our magination always refers the heavenly bodies. But the dy itfelf feems much more diftant from us at the horizon, han when we look diredtly above our heads, fo that it ap- 122 DIALOGUE III. pears to us as a comprefled vault. Between us and th; part of the heavens which is over our heads, there is nc thing to regulate our judgment of its diftance; wheret at the horizon the long feries of intermediate objedts helj us to form the diftance, and make us judge it very grea Hence it comes to pafs, that diftances appear much gfeate! upon a plain than a mountain ; becaufe the equality of th! plain lets us fee every thing that is placed between us an the diftant objedt, which the inequality of the mountai will not fuffer us to do. In the famous picture ©f Correggio, at Parma, fo ill c< pied by the chizel of Agoftius Caracci, who was other heads and feet, place a diftance between St. Catharine an the head of the Madona, fo fenftble,' that you would imr gine it might be meafured by the touch, and which, adde to the other beauties and graces of art all united ther render it a mafter-piece of painting. Now, to finilh our optic comparifon, the antients appe; to us through a long feries of emperors, kings, archon confuls, and many other objects, which greatly magnii them: but we fee the moderns alone, feparated and le entirely to themfelves like the moon at the meridiai] Hence it is, that the manner in which the antients buttonc 1 their coats, will be a fubjedt of admiration to the learnec whereas there will be only two or three men of good fen to applaud any ufeful invention of a modern, who h; the misfortune to be born in the fame age with ourfelve and not to be diftinguiftied by a name with a Greek te mination. And this is the way in which a great part | thofe who value themfelves upon their learning, thin j! Horace very finely fatirized this folly in the time of Augij On Light and Colours. 123 us. So true is it, that a wrong turn of thinking is the rowth of every age. But would not the Chinefe, faid the Marchionefs, be ainers by the immenfe diftance between them and us ? md may not a million of miles produce the fame ede£t as • many fucceffions of kings and confuls ? They are certainly r; 0 lofers by it, anfwered I ; but however, thofe very per- Jbns who moft idolize this nation, which in the midft of bfervators and aftronomers could not produce a tolerable Imanac, agree that we are fuperior to them. This con- i'] d -.{lion perhaps is the effect of natural felf-love. The Chinese : arm a nation entirely feparated and different from us; ,'hereas the antients are as it were of the fame family with ,• urfelves, and we regard them as our anceftors. And ; : fter all, fome few forry thoufand miles can never be e- Jluivalent to a lift of archons or confular Fafti. In Ihort it ; here, as in the compofitions of the theatre, in which eople fuffer themfelves to be much moreeafily deceived in .’hat regards the cuftoms and manners of the antient 'ireeks and Romans, than in thofe of the Turks, or Ja. ..jonefe. . < Another inftance in which this comparifon holds good, etween the antients and the moon at the horizon is, that ie appears the greater to us upon the account of her being :fs refplendent there, than when five is at the meridian, ’hofe objefts which are the fartheft ofF, are the leaft illu- minated. So that if two objedls, are of an equal fize, the :aft illuminated will be thought the moft diftant, and con- :quently the biggeft. Hence trees and houfes appear ! reater to travellers in the twilight, than in full day; the :n feems bigger when feen through a cloud, and objedts mft generally appear greater in England, than they do CO 124 DIALOGUE nr. In Italy. The fun, after the death of Julius Cteflar, tinued pale and languid for the fpace of a year, and accor mg to the expreffion of an elegant poet, threatened th guilty age with an eternal night. If the Romans h; ! dealt in obfervations, I do not doubt but they would ha informed us, that he appeared likewife bigger than ore nary. Objedts then, faid fhe, are magnified by the mii of antiquity : many of thofe great philofophers, who names now pafs for a proverb, were perhaps no more their own time, than the regent of a college, or the le tor of an univerfity. Thofe, anfwered I, who are tl mold devoted to them, are the mod likely to fee them great ly magnified : for, as the fined and mod judicious veri in the world inform us, fools admire , but men of fen; approve; and every thing appears magnified to dulnel as objedts do when feen through a mid. 1 fhould not : all wonder, if fome profound admirer of the Greeks fhou prefer the Epicurean explication of vifion to that of tl moderns, for this only reafon, that one is more antiej than the other. What explication is this, faid the Marchionefs, for I c not remember that you have mentioned it to me before It was the lad I fpoke of, anfwered I, when we were tall ing yederday about the explications which the antien have given of fight. This fuppofes that certain fhadow or images fly oft from bodies, by whofe means we fe> Though this may feem reafonable enough to fome perfon vet there arifes a great difficulty to explain how it happen that when we are in the dark we fee objedts that are placei in the light ; but when we are in the light, we cannot di: :ern objects placed in the dark : fince according to th explication of the Epicureans in both cafes, there are ft?! On Light and Colours. 125 nvs which fiy off from the objects, and raife in us the nl'ation of vifion. Lucretius calls a certain lucid and . btUe air to their affiftance, which, entering into the eyes hen they are in the dark, difengages them from the more lick and black air that obfcured them, and by this means o- ens a paffage to the fhadows which from objects placed in . le light proceed to the eye. When objedts, on the con- •ary, are placed in the dark, the thick black air fills the ; yes, and by this means, denies a paffage to the fhadows hich are tranfmitted to the eye from thofe objedts. , The image of any objedt, faid the Marchionefs, cannot s drawn upon the retina, unlefs there are rays tranfmitted • rom the objedt to the chFyftalline humour, juft as in the amera obfeura, an objedt, in order to have its image ainted upon the paper, muft tranfmit rays to the lens. |f then the objedt be placed in the light, and we in the lark, its image will be drawn upon the retina , and we ball difeern it; but if the objedt be placed in the dark, it .annot tranfmit any rays to the chryftalline humour, there an be no image drawn upon the retina, and confequently he objedt cannot appear to our fight. But I do not fee Ivhat relation there is between the thick or fubtile air of -ucretius, and thefe images. It is true, anfwered I, hat this air has nothing to do with the image on which dfion depends, but it has a great relation to thefe fhadows )n which depends the honour of the Lucretian philofophy. 4nd what is there in the world, that a philofopher, em- I oarraffed in the explication of a phenomenon, does not ay hold on ? But fince you have fo well explained this, I i ivill venture to propofe to you another, which you muft often have obferved; it is, that in going from a very light place to one which is much lefs fo, and may even be cal- ’ L 2 126 DIALOGUE III. led dark when compared with the other, the objedls this place are at firft not at all difcernible, but by degrt they begin to appear, and after fome time are feen ve difi.in.6Uy. This often occafions great miftakes in focietl which are Tery foon found out, and repented of, Ai one, for infiance, going into the chamber of a lady, wh cither becaufe (he is indifpofed or fancies herfelf to be i likes to fit in the dark, may take one perfon for anothe and a fine compliment be wrong addrelfed, and the err< afterwards appear to the great confufion of the perfon wl had been at lb great an expence of wit in forming it. This phxnomenon, faid the Marchionefs, finding, hi very important confequences, and merits the utmoft attei tion. But I mufi confefs, it appears to me a little moi perplexed than the firft, and I do not know how many d« grces of fubtilty in the air Lucretius would require to ex plain it by. Yet the explication of this phxnomenon anfwered I, depends entirely upon a thing which you mui very often have obferved with the utmoft diligence. Hav you never remarked that there are no eyes, not even you own, but appear much finer by night than in the day ! agree to this, faid the Marchionefs, that we may not fpoi. our obfervations by compliments : But does it not proceei from hence, that the night does not Ihew the defedts o the face fo much as the day, and therefor the eyes toe mufi be gainers ? The true reafon of this phxnomenon anfwered I, is, that in the dark, the pupil is more open and dilated, which makes the eyes look blacker and bright' er in the night than in the day, when the pupil is more contradled. How many eyes have triumphed in the even- ing and gained conquefts W'hich they loft the very next morning at the approach of the fun ! The pupil is contrac- On Light and Colours. 127 ed in very light places, in order that it may not admit :oo great a quantity of rays, which would only ferve to 3 o it hurt. On the contrary, it is dilated in the dark, :nough to admit fuch a quantity of rays as are fufficient 0 caufe vifion. The reafon perhaps, why fome animals lever creep out of their holes till evening is, becaufe they ire not able to contrail: their pupil fo much as is neceffary 1 i:o hinder the light of the fun from injuring their eyes. When we go therefor from a light place, to one which nay comparatively be called dark, the pupil, being at fird 'ery much contraded, does not admit fuch a quantity of •ays into the eye, as is fufficient to raife the idea of vifion. The pupil afterwards begins to dilate itfelf, and we begin " 0 fee. And as this dilatation is made by degrees, fo ' We defcern the objedt by degrees (fill clearer and clearer, fill at lad, when the pupil defilfs from dilating itfelf at a certain point, we afterwards continue to dilcern the ob- Wedts with the fame degrees of clearnefs. ! you have not given me the lead time to think on this, aid (he. Who can tell whether I might not have found out his explication, which now at lead does not appear at all difficult to me ? It is fufficient for you, Madam, faid I, to aave explained one phtenomenon, and feen the difficulty >f another. A very great exploit, truly, faid the Mar- ihionefs with fome emotion, to fee difficulties and not be able to refolve them. It is a very great honour indeed for 1 general to bedege a town and not to take it ! No, faid I, )Ut it is fometimes an honour for him not to undertake he fiege at all. The fird dep to wifdom is to ceafe from t olly, and the fird point of learning not to be too arrogant, >ut perceive our own weaknefs. This is a point of mo- lefty very little pradifed by thofe gentlemen who with the l a 128 DIALOGUE HI. vulgar gain the reputation of philofophers, merely by the declaiming in affemblies and coffee houfes, againft tl antient philofophy which they know nothing of but tl name, Stigmatizing thofe who profefs it with the title J Ergotifts, and having read perhaps fame preface or lit|| rary journal. Such fort of perfons never doubt of the knowlege, but explain and pafs a decifve judgment upc every thing. Thefe are blind men who would walk in garden with the fame freedom as other people, but the fir bafon they come to, fall in. There is an obfervatic which the more it is examined, the truer it will appeai that nothing in the world is fo difficult to be met with, ; common fenle. I perceive, faid the Marchionefs, that I have fome righ to call myfelf a philofopher. I have my head full of vor tices; I form light by the preffure alone of the globule of the Second element, and colours by their rotation, have renounced the mod agreeable qualities, and retail nothing but a little extenlion, and infinitely fmall quanti ties. I am not certain whether the world appears th< fame to all eyes : I explain one phenomenon, and fee thi difficulty at leaft of another; I think I have contempt e nough for the antient philofophy ; and after all this, 1 hope it will not be faid' that I am not wifer than I was, Do I want any thing elfe to make me a complete philofir pher ? — Yes, Madam, anfwered I, perhaps you Should! have a little lefs beauty, or make a better ufe of it. But •you do not perceive that the philofophy you are fo fond ol needs a reformation, and 1 wiih this reformation might be the laft. What, faid She with fome emotion, will you tell me that Vifion is not performed in the manner you have On Light and Colours. 129 hitherto explained it? This is plainly betraying me, and affirming upon your word, what afterwards ap- pears not to be true. No, no, Madam, anfwered I, be aot uneafy, I am not of a chnrafter to propofe to you :hings differently from what they are. Vifion {hall re- nain untouched; that abjuration, which you have gene- -oufly made of the rofes and lilies in your cheeks, fhall band good and be ratified in form. The doubts you are under, concerning the different appearance of objefts in I different perfons, {hall ftill continue to be reafonable, and your preferring the moderns to the antients, fhall ftill be :ompatible, and remain as it is founded on the very beft 1 reafons. The reformation I fpoke of will affeft nothing but the globules of light, and the manner in which they excite in us the fenfation of colours. You may hereafter f you pleafe regard the fyftem of vortices, as one of the pneft and mob entertaining philofophical poems in the world, which is the idea under which I at firft propofed it :o you. This is abfolutely difconcerting my ideas, faid the Vlarchionefs. 1 would willingly look upon this fyftem as i omething more than a fable, were it ever fo fine a one. ; cannot think of changing any thing in the globules of ight, which with fo very little trouble fupplied me with he moft agreeable colours. If I once quit thefe, who mows how much pains, and how great an apparatus it I svill coft me after this to make even a lorry metzotinto ? It will coft you no more, anfwered I, than it did with your globules. This reformation was produced by father Malebranche ; one of the greateft and moft illuftrious Car- :efians that ever appeared in the world. The authority I af fo great a name may let you fee, how very neceffary this reformation was, and you may moreover be fure that ;he funplicity which has always formed the delight of this *3° dialogue iii. fe<51 cannot fail here. This fimplicity is an idol, t which they facrifice every thing, even truth itfelf lornc times, that truth, which an antient called the citizen c heaven, and companion of the gods. But before I procee< | to this reformation, it will be proper to lay before you th great difficulties which mull make you for ever renounc | your globules. This fyllem, like Hercules in the fable had very great difficulties to encounter with from itsverj birth ; but perhaps it did not overcome them with equa honour. i Some objected, and with great reafon, that according to thofe laws affigned to the vortices by their inventor him felf, as the liars are not compofed of the fubtile matter!; but of that of the third element, inllead of being luminous, they would be covered with an opaque cruft ; and even il they were luminous, the contrary and equal prefture of the vortices would not fuffer us to fee them. However weighty thefe objedtions might be, they would not be able to lhake the faith of the Heady Cartefians. But j this, which I am now going to mention, appears an indif- foluble gordian knot, even to the moft zealous and ardent! among them, You have this formidable enemy of the Cartefian philofophy in your own houfe, nay, in the very gallery where we are, and you do not perceive it. This;! painted wall is an adverfary that makes war againft the fyllem you are fond of. Deliver me from this perplexity, j I intreat you, faid the Marchionefs, or I fhall erafe the picture. You have a mind to make me quarrel with my; own houfe for prelenting me with fuch deteftable objedts. |j No, Madam, anfwered I, finding, that is not my inten- tion ; I would rather have you perfuaded that every corner |! of it is fince yefterday become philofopbical. Let us fix upon one point in the air to which your eye On LiGHt and Colours. I3 1 md mine may be equally directed while we are both look- ng at the fame time upon different parts and different :olours of this wall. Do you, for inltance, place your- felf at this pilafler, and look upon the red on the vefture of Achilles. I will hand at the window, and look upon the • blue of the fea ; fo that while you are looking at the red md I the blue, our eyes may each be direded to the fame . uoint of air. It is certain, that two rays will pafs through this point, one from the robe of Achilles, and the other from the fea. Thefe rays you know are nothing but two feries or firings of globules immediately touching each other, the one continued from the robe of Achilles to your eye, the other from the fea to mine. Thefe two firings of glo- bules interfeft each other in that point which we have fixed in the air, and confequently in this point there will be one i globule common to both firings. Do you underfland all ' this ? Yes, too well, faid fhe, and I begin already to trem- ble. In order for thefe globules to excite vifion in us, an* fwered I, the preffure of thofe contained in that firing, which comes from the robe of Achilles, mufl be continued from thence to your eye, and the preffure of thofe contained . n that firing which comes from the fea mufl from thence be continued to mine. Now that globule, which happens to be in the point of air, where the two firings interfe<5l, and which is common to each of them, mufl at the fame time prefs towards your eye and mine, which is utterly impoffible if the globule be hard, as Des Cartes fuppofes it to be ; becaufe the clofe union of the parts of fuch a body can never fuffer it to prefs at the fame time towards two different fides. But this is not all. And yet this is fufficient, faid the Marchionefs, to demolifh my globules. ■ The very fame globule, faid I, as hard as it is, mhft have 132 DIALOGUE III. I at the fame time two different rotations, one to excite it you the idea of a red colour, which is communicated tc the whole firing that comes from the robes of Achilles tc your eye, and the other to excite in me the idea of an azure colour, communicated to the whole firing that comes frorr the fea to my eye. But the difficulty will be ftill greatei| if we fuppofeother fpedators to be placed in this gallery; who all direifi their eyes to the fame point in the air, a; W 7 e have fixt upon, and other rays to pafs through thi; point, fome of which fhould convey the golden colour ol Achilles’s hair, that Minerva lays hold on in order to calrr his deftru<5Hve and impetuous rage ; others the green of thii meadow, and the innumerable other colours which varie- gate the pidture. You fee then, that fuppofing your glo- bules, fuch as Des Cartes has made them, it would bt Impomble for us to fee what, however, we really do fee, I underhand this but too well, anfwered {he ; but I befeechj you, for the love of philofophy, never mention thefe glo- bules to me again. I am refolved to think no more of them! fince they have fo fhamefully yielded to the very firft diffi- culty. They feem to refemble thole unexperienced lovers, who at the firft. repulfe think of a retreat. But pray let me fee what your reformed Cartefian Malebranche fubftitute! in their place ; for I am perfuaded he will be able to make a better refiftance. Malebranche, anfwered I, entirely reje&s thefe folid globules which you have forbid me to mention, and fub ftitutes in their place certain exceeding fmall and fluid vor- tices compofed of an ethereal and very lubtile matter, whicl, fills all the great vortices, as the great vortices which arc the feats of ftars and light do the univerfe. Thefe little vortices, by that power which they have of dilating them ! On Light and Colours. 133 I elves, keep a mutual equilibrium in their refpe&ive vor- :ices, juft as the great vortices do in tne univerfe. In this fyftem of Malebranche, light is nothing but the undulati* jn or vibration of the vortices, occafioned by the vibration of the luminous body which is always repelled in the fame moment that it impels ; and the greater or lefs force of the ight depends upon the greater or lefs force of thefe vibra- :ions, juft as colour depends on their greater or lefs velo- city. For inftance, if thefe vortices fliould rail'e fifty vi- brations upon the optic nerve of the retina, in any deter- minate fpace of time, it would give us the idea of a certain colour ; if in the fame time there fhould be a greater or lefs : number of vibrations raifed, we fhould have the fenlation of a different colour. Malebranche ingenuoufly confeffes however, that he was not able to affign what determinate : idegrees of quicknefs were neceffary to form different co- lours in particular. A confeffion fo much the more in- genuous as it is extraordinary in a philofopher. ' This fyftem of light and colours has a very great affini- ty with that of found, with this difference only, that air is the vehicle or channel of the one, and ethereal matter i or the vortices compofed of that matter, the channel of the • other. The vibrations, which a fonorous body when it is ftruck, raifes in the air, and from thence in the auditory nerve, excite in us the idea of found. In the fame man- ner, the vibrations which a luminous body raifes in the ethereal matter, and from thence in the optic nerve, ex- cite in us the idea oflight. If the air be entirely excluded from any place, which may be done by the help of a certain machine, a fonorous body put into that place would not be heard to found. In the fame manner if it were poffible to exclude the ethe- 134 DIALOGUE III. real matter from any place, a luminous body put into that place would not appear refplendent. The greater or lefs force of the vibrations on the air, or the auditory nerve, produces a great or lefs intenfenefs ol found. In the fame manner the greater or lefs force of the vibrations on the ethereal matter, or the optic nerve, produces a greater or lefs intenfenefs of light. j The different quicknefs of the vibrations on the air, or the auditory nerve, produces different founds, as bafs, treble, and their different degrees ; fo after the fame man- ner, the different quicknefs of the vibrations raifed in the ethereal matter or the optic nerve produce different colours, as red, yellow, and the like, which may be confidered as the tones of light. I do not believe, faid the Marchionefs, that even our preachers ever carried a fimilitude farther than this. It may be carried ftill farther, anfwered I. As various and different vibrations crofs and interfe<5t without deftroying,! or rather, without giving each other the leaft interruption which we every day fee in conforts of mufic, where the vibrations of the firings of a violin do not interupt / thofe of any other inftrument, fo the different vibrations, < which flow to our eye from different colours, do not inter- rupt each other, notwithftanding they crofs and interfeft. The fluidity of thefe vortices gives them a power of tran- fmittingthe vibrations of different colours to various parts, which the folidity of the globules would not fuffer them to - do ; in the fame manner as the fluidity of the air does the different founds in a concert of mufic. The explication of t this feems fo very difficult to Malebranche, that he affirm- ed a fyftem, capable of effecting it, muft be conformable to i truth. On Light and Colours. 13d Sound and light, replied the Marchionefs, appear to be ■ is faithfully copied from each other, as nature was by the [paintings of Apelles, which were fo very accurately done, :hat an aftrologer could predict the future fortune of the :3erfons whom they reprefen ted. I have not yet finilhed the comparifon, anfwered I. An pbjedt, placed between two looking glaffes over-againft each other, will be greatly multiplied. One candle is changed into a thoufand, and brings to mind the celebrated annual feaft of the illumination of candles among the Egyptians, [ from which, fome imagine the Chinefe to have borrowed their feaft of lanthorns. And does not the famous echo of the caftle of la Simonetta, not far from Milan, produce ( the very fame effect upon found ? The report of a piftol in this place is repeated more than forty times, and a fingle inftrument of mufic forms a fffinefs of found fuperior to that of the mod numerous concert. T wo great wings of a f building oppofite to each other with windows, which are ail falfe except one, and formed of a matter very proper i to throw back the vibrations, refledt and multiply the found ! i juft as the two glaffes do the candle. The great lord Bacon, the harbinger of true phiiofophy, has among innumerable other curious things, propofed the examination of this affinity, betwixt light and found, to the confideration of naturalifts. Perhaps he could not ft have wiihed to find a more clofe union betwixt them, than what the fyftem of Malebranche difcovers. But he advifed too, that philofophers fliould carefully examine in what points they might difagree ; and the greateft difference betwixt them is, as I firft told you, that the channel of found is the air, and that of light the ethereal matter. Hence it follows, that found rnufi be propagated from a M 136 DIALOGUE III. fonorous body in time ; for the fpaces and inteftices betwei f he particles of air make it abfolutely neceftary, that the ftiould be fome little time before the motion can be con municated from one particle to another. Light on tl contrary mult be propagated in an inftant, or an exceec ing little fpace of time, becaufe there are no fpaces betwij the vortices or ethereal matter, fince the whole univer;| is every where filled with them. Light and found hay the lame refemblance to each other as the Nereids engrav ed by Vulcan upon the filver gates of the fun’s palace, ij Ovid’s Metamorphofes. Their features are not exadtly th 1 fame, but fo extremely like, but it is very eafy to perceiv they are fitters. | Let us then become reformed Cartefians, faid the Mar chionefs, by accepting a reformation which not only ex plains all that the globules did, but fomething more, and of much greater importance, which they were not abli| to explain. Let us adopt Malebranche’s fyftem of light and found, thefe two new brothers in natural philofophyl I do not abfolutely defpair, anfwered I, but the harpficorci of colours, and the mufic of the eyes, which gives a ftill! greater confirmation to this new alliance, may in time meet ■with a favourable reception from you. What do you mean, replied the Marchionefs, by this new invented mufic and harpficord ? Have you a mind to ridicule the philofophical fimilitude you have been enter- taining me with ? I Ihould be forry, anfwered I to have any temptation to ridicule what you have adopted inftead of your globules. This harpficord is indeed a new inven- tion, but is not therefor the lefs true or real. Upon mov- ing the keys of this inftrument, inftead of hearing founds, you will fee colours and mezzotintos appear, which will On Light and Colours. 137 roduce the fame harmony as founds do. The fonatas of Yameaux or Corelli will give the fame pleafure to the eyes 'hen feen upon this philofophical harpficord, as they do 1 the ear when they are played upon the common fort, 'he concords of a piece of purple and fcarlet will raifc ie paffions of love, pity, courage, or anger in our fouls : lis furprizing inftrument is now making beyond the moun- tins, and you m2y for the future expedt your filks and ibbons in mulic. The tranfient pleafures of the ear will e fixed in the eye ; you may continually enjoy the fine airs f Farinelli wove in a piece of tapeftry. The inventor, anfwered Ihe, probably took the firft; dea of this, from the drefs of a harlequin. However, we •’ re greatly obliged to him, for we lhall have no occafion 0 embarrafs ourlelves for the future in adjufting the colours : if our clothes. We need only confult the thirds and oc_ aves of this harpficord, and we lhall be fure never to make my difcord in the lhading. The painters, anfwered I* nay find relief in their indifpofitions from this new invent- d mufic of colours, as fingers and muficians are faid to do rom that of founds. ! Why will you reftrain the effedts of fo lingular a thing, aid Ihe, to the painters only ? It will help phylicians to ncreafe their prefcriptions and prolong their confultations. phylicians, anfwered I, mull adl with regard to their pa- tients, as muficians do with weak voices ; and as thofe are :areful not to difcourage their fcholars with difficult notes, o thefe in certain difiempers, as the bite of a tarantula* which can be cured only by pleafure, mult take care not o prefcribe any colours for which the patient has an a- /erfion. But we iriuft leave the phyficians to divert their patients in this new method as they judge proper. This M 2 J 3 8 dialogue III. new inflxument will help to give us a proof of the juftnej of that fine companion made by an elegant poet betwee th^ giadual languifhing and dying founds in the voiced! our tuneful Orpheus, and the infenfible fading and vanilll ing of the colours in the rainbow. Who knows, replie the Marchionefs, but we may fome time or other form I dinner by the affiftance of a harpficord, and find harmon in a fricaflee ? After this difcourfe, as we are taking the air in the gab den, the Marchionefs fuddenly cried out, — What fhall w do ! I fee a gentleman in the neighbourhood coming tc wards us, who in every vifit he makes does me the favou to repeat fonnets by the hundred, and yet always find time for fome ode. How fhall we difengage ourfelves fror his troublefome company ? Will there be no vortex fo mer ciful as to fnatch him away with itfelf, and remove hin from our fyftem ? For want of a vortex, anfwered I, wii will ferve him as I once did a mathematician, who hap pened to be very talkative, a fault which thofe fort of peo pie are feldom guilty of. Wlhen you are walking with friend, and difcourfing about the country of Kouli Kan, 01 fome fuch trifle, he will entertain you with the molt ab ftrufe points in geometry. He alfaulted me one day as 1 ! | was walking with fome company in a garden, and wc prefently found by his air, that he was preparing to tor- ment us with his demonftrations and corollaries. I and 1 the others who were with me began to talk of poetry, and repeat verfes, a language to which he was an utter flranger, without fuffering him once to open his mouth, B y this means we compalfed one of the moll difficult enter- prizes, that of tiring the moft tirefome perfon in the world. Now we need only continue our difcourfe upon philofophy, On Light and Colours. 139 id I will engage your fonnetteer will fuffer the fame pu- :fhment as my mathematician. Thus we refolved to pro- ved. After the firft compliments were over, the poet, who new nothing of our fcheme, took occafion to inform us, lat the mufes had for a long time ufed him ill, and that mi e was refolved to renounce them for ever. After we had villy contradiffed him, he anfwered, that he was ready " i prove his affertion by a few fonnets which he had lately ll lade, and which would fhew us, how very little he was 1 their favour. If they are really fo perverie, faid the d llarchionefs, taking him at his word, you mull entirely bandon, and never think of them again. We have juft een diicourfing on philofophy and optics; it will be taking effectual revenge if you enter into our converfation, kich is fo very different from poetry. He excufed him- :lf by faying that he had not a capacity for fuch fublime ibjedts, and though it was neceflary fometimes to fhew a [ ttle refentment, he muft take care not to affront the mu- I is too much. He obferved that a little poetry would aile- iate the feverity of our philofophical difcourfes, and al- ;ged the example and authority of Plato, who did not kink it beneath him to write love-verfes to Agatis, and ngrave the three Graces on the citadel at Athens, with he fame hand with which he had wrote the inltitutions f his Republic, and the Timeus, and in this manner di- ided his time between philofophy and the arts of. Apollo, lut all thefe arguments could not prevail on us to let him epeat his fonnets, which was the chief defign both of his Hits, and all that erudition which he had lavifhea upon us. The Marchionefs alked me feveral queftions, which our loetdid'not think at all a-propos. Among the reft,, fce m a Mo D I A L O G U E III. was very anxious to know whether fhe might rely upcj Malebranche’s fyflem of light and colours; for the d {fraction of the globules made her fear every thing, ai her fuipicions were terribly increafed by this harpficor 1 anfwered, that fuch was the condition of all hum; things, that nothing mull; hope for a long duration he: below, a truth which our gentleman could evince by mar fine verfes of the belt poets, and perhaps by fome of h own. I added, that I was extremely pleafed to find tl example of the globules had w'arned her not to place tc much confidence in the reformation of father Malebranch But that the moll fatal blow to this opinion was,- the b ir.g obliged to forfake it upon the account of that Very ;fn; logy and correfpondence betwixt light and found, whit at firft feemed to give it fo much lullre. " This analogy, continued I, fails in one of the part! and in that part where it was molt wanted. And.th circumftance is fufficient to' overthrow Malebranche’s rc formed fyflem. All tbofe fine refemblances, - which' yo ebferved with fo much admiration, cannot fave .it fror deRrudcion. if an undulating motion happens tp meet with any ob {facie in its way, this does not flop its progrefs, for i bends on all fides, and continues to propagate itfelf f fpite of the obftacle that oppofes it. _ A very familiar example will make you underlland wha I mean. If we were at the bottom of this hill, and fom perfon on the oppofite fide of it fhould found a French horn to proclaim the deftrudlion of. fome innocent tenan, of the v.’oods, whofe only fault is the pleafure we find ii deftrcying him by the help of ourreafon and contrivance we fhould hear this found notwithftanding the whole hi! I On Light and . Colours. 141 ; placed betwixt the horn and our ear. The reafon of his is, becaufe the undulations raifed in the air by the 'rench horn do not flop their progrefs when they meet with the hill, but giving way on every fide and bending till round it, communicate the like vibrations to the oppo- ite air. After the fame manner, if you throw a little done nto this bafon, the undulations formed in the water will lot flop when they meet with the pipe, but giving way dl round it, will communicate themfelves indifferently to ; ill the water, and thus the effedts of it will be dikovered n the whole bafon. You.fee then that if light were nothing but an undulation . of .the ethereahmatter communicated to it by the vibrations . af the lucid body, no interpofed body could ever deprive ,us of the light -of the fun or any other luminous objedt, or in. other words, we fhould never have any fhadow, which, .1 Specially in this feafon, would be a terrible inconvenience brought upon us by jVIalebranche’s fyftem. Thepre/fure 6f Des Cartes’ globules could give us no a Alliance in this cafe. .Thus Sir Ifaac Newton, the avowed enemy of imginary iyllems, and to whom you. are indebted for the true idea of philofophy, has at one blow lopped off the two principal heads of the reviving Cartefian Hydra. | Though the M.trchionefs perceived the force of this argument fhe did not feem greatly difpleafed with it. As fhe had renounced the globules, fhe eafily gave up the vortices. But our fonnetteer was not quite fo well fatisfi- , ed. As he could find no opportunity of difcharging his poetic fury, he was obliged to go fome where elfe, to find w an audience to a fa tire,- which it isvery probable he had be- - gua to compofe agaiaft philofophy. [ I 4 2 ] dialogue IV. Encomium on Experimental Philofopby , and an Expoftioi of the Newtonian Syfem of Optics. H E next day when we had difengaged ourfelves from poetry, which had at firft given birth tc our difcourfes on light and colour, and afterwards' endeavoured to dillurb and interrupt it, I began af- ter the following manner. It is now time, madam, to lead you into the mod retired fan&uary of philofophy, from whence the prophane and thofe who are filled with vortices, globules, atoms, fubtile matter, and like imagi- ' nations, are entirely excluded. This philofophy, which I am now conducing you to, is lefs pompous than that we have already difcourfed on, but in return performs all its promifes ; a philofophy, which is contented with giving a hiftory of phvfics, and leaves to others the province of making them the fubjeft of a romance. You have had an inftance of the one in its method of explaining the nature of vifion, and the fyftem of vortices has given you an ex- ample of the latter more pompous and fplendid philofophy, which boldly goes to the firft caufes of things, and laying down certain arbitrary principles, upon thefe builds the world, and explains all the phenomena of it according to its own fancy. As the eye is now difcovered to have an entire refem* blance to the artificial camera obfcura , all philofophers will hereafter explain the nature of vifion after the fame On Light and Colours. 143 ianner. But there will not be that conformity in their pinions concerning the folidity of bodies, gravity, light,' nd colours, fince the caufe of thefe qualities can be known nly by conje&ure. And how very hazardous a thing this ;, you have already feen in the Cartefian fyftem of glo- mles, to fay nothing of Mallebranche’s reformation, which, lot with (landing all the applaufes at fir ft given it, is now xploded, and Ihares the fame fate as the globules. And his you may believe has been the cafe with all the general j yftems that have hitherto appeared, concerning the caufes )f things. They refemble vaft empires, which totter and all by their own weight and greatnefs. I find then, faid he marchionefs, that the wherefore, which fo greatly ex- :ites our curiofity, will be for ever hid from us, and the jleafure of conjecturing, which is generally fo adapted to ■ he tafte of men, will have no charms for philofophers. This really is a circumftance, which will make the condi- :ion of thefe gentlemen not greatly to be envied by the vul* jar. !• Conjecture, anfwered I, according to the aftertion of one )f the moll ingenious authors in the world, is not to be al- 1 lowed in any thing but geometry. In this fcience, if the certainty of principles does not direCtly guide us to what • we feek, it never leads us however to any thing contrary, and always rewards our fearches with fomewhat equiva. lent. But what uncertainty and inconftancy is there in natural philofophy? Some affirm that there is a vacuum, or fpace void of all body, and others will have every thing to be body. This diverfity of opinions, with regard to principles, mull unavoidably produce very great and in- numerable difputes as they advance further, which extend fo far as the fixing the elfence or nature of body, a thing DIALOGUE IV. 144 which one would imagine Should of all others be the me certain in phyfics, fince body and the properties which di pend on its efience, are the perpetual fubjedt of philofoph cal inquiries. I cannot help comparing thefe philofophe: to thofe critical writers who corredt fome corrupted and d< fedtive pafiage of an ancient author. One of thefe gentli men gives one reading, a fecond another, each fupporte with the fineft and molt elaborate arguments, and the en comiums of the joumalifts of the learned. Some old ma nufeript of the author at length appears drawn out from th dull and obfeurity of a library, and then all the fine read ings of thefe profound critics, and the time they fpent ii inventing them, are fent into the regions of Ariofto’s moon and are there treafured up among other loft things. Ob fervations and experiment are the authentic anchorigina manuscripts of nature ; and thefe, by overthrowing fo ma 1 ny fine fyftems, inftrudt us every day to be more cautiom in puzzling ourfelves to form hypothecs. I look upon this advice as a very great benefit to mankind, fince it ex* empts them from no fmall trouble and fatigue. But the misfortune is, that men perfift in arefufalof this friendly admonition, and are obftinately bent to fpend their time to no purpofe. This is indeed a praftice that redounds greatly to the ho- nour of thefe obfervations of yours, faid the marchionefs. A fyftem need only be ingenious, fimple and elegant, to give them a right to declare open war againft it. They may be termed the Eroftratufes of natural philofophy, who found their glory in the deftruflion of all that is great and fplendid. I mull confefs that I cannot be pleafed with fo malicious a character. To what a height would your dif- On Light and Colours. MS reafure rife, anfwered I, if I had told you all that theft nfervations are capable of effedting. There is perhaps no Hern better grounded than this, that animals have wings ven them in order to fly, and legs to walk. And yet ob- 'vation has difcovered to us certain infedts who have large ings without making ufe of them to fly with ; and in the me manner, there is one animal, which, notwithftanding has legs difpofed like t^hat of others, formed in the fame anner and of the like proportions, yet almoft alway s alks npon its back with its legs upwards, juft as if the firft re not fenflble they had wings, nor the laft, legs. It true, however, that if oblervations had done no greater vice to the world than to deftroy, we fliould not be much debted to them. But by overthrowing perplexed and lefs, and fometimes very troublefome fyftems, how ma- sood and ufeful difcoveries have thefe obfervations fur- 0 hed us with, in the room of thofe hypothefes they have erthrown ? Some melancholy philofophers have imagined the rays of e moon were cold and humid, and therefor greatly to be red, fince there mull be expedted very dangerous effedts >m their influence. And in fadt you fee many perfons, jbn now, who, believing the effedts of this planet from the idition of their fore-fathers, retire as foon as ever the moon gins to rife, and, as they exprefs it, gets ftrength ; and ft numbers of people are perfuaded that they have the id-ach, if by walking in the evening they have unhappi- been obliged to receive the infedtion of its light. The experiments, which have been made upon this, give 1 full liberty to walk at what hour we pleafe, without ap- j ihending any danger from that quarter. The rays of this f .net, colledted in the focus of a burning glafs or a lens, do 146 DIALOGUE IV. not caufe any fenfible effedt in the bodies upon which t] fall, notwithftanding they are fometimes two thouf; times denfer when thus colledfcd, than they ordinarily i A thermometer, which is an mflxument containing a quor that contradts with the leaft cold, and dilates w the lead heat, does not fuffer an alteration in the focui thefe glades when they are expofed to the rays of the mo< whereas, if they are expofed to thofe of the fun, the ■ hemency of their heat furpaffes that of the hottefl: f'urnac fo that the amiantus , which defended the precious al| of antiquity from the devouring flames of the funeral p cannot defend itfelf from the violent heat of thofe glal The rays of the moon do not appear to have any otj quality, than that of fupplying the abfence of the ft andinfpiring afoft and pleafing melancholy in the heal of lovers. Thefe forts of obfervations, faid the Marchionefs, I h: no objedtion to, which let the fine fyftems alone, and 1 liver mankind from ill-grounded fears. To this fp of obfervation, anfwered I, we are indebted for our 1 liverance from other much more impotent fears ; comii pillars of fire, fhowers of blood, and ignes fatu'i , ancienj marks of divine wrath, do not at prefent difturb fc mt as one half hour’s deep, except it be in thofe perfons, v, will always be the vulgar, and always of a tempter fit to receive thefe impreffions of terror from others. But how much are we indebted to the ftudy of exp< ments ! Aftronomy, natural Hftory, and anatomy, fc by the affiftance of this to be rather new fciences born!’ mong the moderns, than tranfmitted from the antientsj) us. To this, anatomy owes the circulation of the blob and all the animal occonomy, whofe very fimplicity was .4 On Light and Colours. 1 47 nufe of its being fo little known among the antients. To as, chemiftry is obliged, for its phofphorus . aftronomy , i' its exaft predictions : hydroflatics, for an Cal y metnod 'living, and carrying frefh air for refpiratiqn, in an ele- ' jient denied to men: for acouftics,’ and their fpeaking - ■umpet; their projects, for rendering the perfection of mj earing equal to that of fight, and innumerable mufical dtruments, the offspring of harmony. To this optics we their telefcopes, microfcopes, magic lanterns, and n infinite number of other wonders, that perfeCt or flat- :r the fenfe of feeing. Superftition, credulity, and a greater love for the mar- llous than truth, negligence, and a want of proper leans for obfervation, have for a long time been infuper- ble obftacles to knowlege. How great a treafure of won- ers has natural hiftory, after having rejected the abfur- ities of the antients, demonftrated to us ! New modes of reduction, breathing, feeing and living, new conforma- on of parts, new focieties, new modes of being, unheard tad unknown to paft ages. The reafon of mankind has been poiifhed in proportion ; that of brutes has been more confidered ; and the arts lemfelves have been brought to perfeCttion by obferva- on upon certain animals, commonly regarded either with orror, or as the refufe of nature. Spiders have furnifhed iur manufactures with new fpecies of filks ; and the egg s f a fifh, though yet unknown, may, with a little appa- atus, give us a fine purple colour not inferior to that fo iuch celebrated by the antients. Shall I inform you of he experiments made concerning the weight of air, and he power it has of dilating itfelf when compreffed ? expe- iments once termed the wonders of Magdebourg. Shall N 148 D I A L O C U E IV. I give you an account of the equilibrium of fluids, vegetation and culture of plants, which have afforde great an advantage and ornament to fociety ? By t experiments your garden is embellifhed with the pla and agreeable murmur of artificial fountains; and t fupply the northern tables in great plenty with thofe < cious fruits that nature had confined to a warmer ht lphere. The orange, by thefe tranfported from Chin the Portuguefe foil, Aveetly allays the burning heat of fummer ; and thefe experiments have extracted from vines of the Rhine tranfplanted upon the burning rock Canary, that agreeable juice fo pleafing to the tafte of dies. Still better and better, faid the Marchionefs. | not this the clufter of the promifed land by which hope to allure me ? and as we are in the country, wei intice me, by the hopes and advantages which accrue ft obfervation, to agriculture and oeconomy ? Without | pute you have thofe antient confuls in your head, v from the triumph returned to the culture of their farn If I had a defign of inticingyou, anfwered I, Mad; 1 fhould rather entertain you with talking of the polite i of which, you are fo fond, and which owe both their c ; ginal and progrefs to obfervation and imitation. Gn tude requires you to think yourfelf obliged to thefe for t pleafure you receive from the fine lineaments and eleg: air of countenance in the Medufa of Strozzi, the juft g dationof the anger of Achilles, the variety and ftrength paffions in Caffandra, that mafter-piece of the Timothc of our age, the majeftic folidity of the Portico of the F tunda, the elegant ftrokes of Guido, and the magic