NORTHWESTERN UNIVF
NO RT H W ESTERN
UNIVERSITY
L I B R A R Y
E VA NSTON
ILLINOIS
b- 7/ /GU
No. 10 '
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THE CONTRIBUTION OF THE UNITED STATES
COAST AND GEODETIC SURVEY
TO GEODESY
BY
WILLIAM HENRY BURGER, C. E.
Professor of Civil Engineering of the College of Engineering,
Northwestern University, Evanston, 111.
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I DEC 7
V' I , -
Reprinted from the Centennial Celebration of the United States
Coast and Geodetic Survey, April 5-6, 1916
washington
government printing office
1916
THE CONTRIBUTION OF THE UNITED STATES COAST AND GEODETIC
SURVEY TO GEODESY 1
By William Henry Burger, C. E., Professor of Civil Engineering of the College of
Engineering, Northwestern University, Evanston, III.
In the earlier days of the Coast Survey, whose centennial is now being
commemorated, the geodetic function, as such, was little in evidence.
It was then simply an aid in carrying on the work outlined in the act
of 1807, which provided for a survey of the coasts of the United States,
in order to provide accurate charts of every part of the coast and
adjacent waters.
Upon the reorganization of the Survey in 1843 the corner stone was
laidfor that fine systemof geodetic works which theSurvey has at present.
In this reorganization two very prominent features, from a geodetic
standpoint, are to be noted. The first is the man who was the dominant
figure in the board of reorganization and the second is the principles he
advocated. Probably no other man has had the influence upon the geodetic
operationsof theSurveyas had Superintendent F. R. Hassler, and probably
no one thing has been of such importance to these operations as the sci¬
entific methods proposed by him. To him belongs the credit that to-day
the operations of the Survey are bound together by a trigonometric
survey with long lines and executed by the most accurate instruments
and the most refined methods, rather than being correlated by purely
astronomical observations. Due to his farsightedness, the best of founda¬
tions was thus laid for geodetic operations, and from this time geodesy
became an important part of the Survey's work.
A further impetus was given to the work when, shortly after the close
of the Civil War, Congress authorized a geodetic connection between the
Atlantic and Pacific coasts of the United States. The result of this was
the great transcontinental arc of triangulation along the thirty-ninth par¬
allel of latitude, one of the most famous arcs in the history of geodesy and
one which has helped to place the United States in the front rank of the
nations carrying on geodetic operations. One of the immediate results
was the recognition of the geodetic function as an important part of the
Coast Survey's work, and in 1878 the Survey's title officially became
"The Coast and Geodetic Survey."
'Address delivered at the Centennial Celebration of the United States Coast and Geodetic Survey at the
New National Museum, Washington, District of Columbia, Apr. 6, 1916.
4428210—16 13)
4
TRANSCONTINENTAL ARC
The great triangulation system along the thirty-ninth parallel is
probably the greatest single contribution to the world's geodesy that has
been made by any one country. It marks an epoch in the scientific
history of the United States and in that of the world. The results of the
work are most important and far-reaching to geodesy, geography, geology,
and the other earth sciences.
It is the longest arc of a parallel ever undertaken by a single nation,
being more than 48° of longitude between its extremities, or about one-
eighth of the earth's circuit, and is more than half the length of the com¬
bined arcs (measured by various nations) used by Clarke in deriving
the figure of the earth in 1880.
The nature of the country traversed by the arc developed new ideas in
reconnoissance, signal building, triangulation, and methods of comput¬
ing, which have had an important bearing on all subsequent work. By
means of it unity and consistency have been secured in the geodetic work
of the Survey. It has proved a bond between the many separate parts
of the Survey's work. These, at first, existed as a number of detached
portions, in each of which the datum was necessarily dependent upon the
astronomic observations. The transcontinental triangulation joined
these detached portions and made them into one continuous system
dependent upon the same geodetic and astronomic data.
From a higher scientific standpoint this arc is a great contribution to
geodesy in giving data for the determination of the earth's shape and
size, but, like any other arcof a parallel, it must be combined with an arc
in the north and south direction to obtain its full power in this respect.
EASTERN OBLIQUE ARC
In the eastern oblique arc the United States has another arc of note,
which covers some 220 and extends from the Bay of Fundy to the Gulf
of Mexico at New Orleans. This was the direct result of Ilassler's plans,
was the scene of his last labors, and had for its main object the binding
together of the detached surveys of the harbors on the Atlantic coast.
Unlike the transcontinental arc, it has all the elements necessary for
the determination of the figure of the earth. It is the first arc which
made use, on a large scale, of measurements oblique to the meridian. One
of its great effects on the geodesy of the United States was that through it
came the rejection, in 1880, of Bessel's spheroid of reference and the adop¬
tion of the Clarke spheroid of 1866 as the reference spheroid to be used
by this country.
ASSISTANT CHARLES A. SCHOTT
Many men took part in furnishing the data for these two arcs and in the
resulting computations, but no name stands forth so prominently as that
of Assistant Charles A. Schott, the " Grand Old Man," who for more
5
than 50 years was identified with the work of the Survey. His labors in
the field and office did much to bring this work to a most successful finish,
and it is fitting that credit be given him for the two monumental volumes
of results which it was his privilege to see completed before death came.
For this work, and for the work done in many other lines of the Survey's
activities, I do not hesitate to mention the work of Mr. Schott as one of
the great contributions made by the Coast and Geodetic Survey to the
geodesy of the world.
The Survey was particularly fortunate in having such a man in charge
of geodetic work, one who could see the full wisdom in the plans of Mr.
Hassler, who consistently worked for their fulfillment, and who was able
to have these plans transmitted to his successors, Assistant John F. Hay-
ford and Assistant William Bowie. This furnished a continuity of plan
which probably stands unrivaled in the scientific history of the world,
and has been one of the big factors in the great success attendant upon
the geodetic operations of the Survey.
RECENT TRIANGULATION
Since the completion of the two arcs mentioned, the Coast and Geodetic
Survey has added many more arcs to its system, until the total length of
the combined arcs is more than 150° of a great circle of the earth, or about
three-sevenths of the circuit of the globe. Incorporated into the system
and placed on one datum are also the many miles of coast triangulation
of the Survey and much of the triangulation executed by the Lake Survey
and by the United States Engineers, until now the system stands without
an equal in any nation.
In the closing years of the last century a new era in geodetic operations
by the Coast and Geodetic Survey was begun. The work of the past was
searched for the best in instruments and methods, field and office methods
were standardized, limits of accuracy were set, and where it seemed
advisable new methods and instruments were devised to meet the chang¬
ing conditions of the work. This era may be characterized as a period
of great speed and low costs, with the previous accuracy maintained.
Never before had triangulation been executed with such rapidity and
with such economy in operations. It is significant that this was attained
without a reduction in accuracy and, in fact, had the effect of an ultimate
increase in accuracy, for, owing to the speed, many more circuits could
be added to the network, thus strengthening the whole system.
As an example of the speed and economy of operation in this last
period the Texas-California arc of about 20° is cited. The reconnoissance
on this arc was done by two men in 145 days and the primary observa¬
tions in a total of 183 days at a cost of $400 per station and of $32 per
mile of progress. Nearly 50 years were spent on the transcontinental
arc of 48°, with a cost of $2,000 per station and $200 per mile of progress.
This comparison is not intended to be derogatory to the latter arc, for
6
the work on that are was the best of any up to that date, and it was only
through its work that the economy and speed of the later work was made
possible. It is believed that no extensive arc in any other country
equals the Texas-California arc or some of the other recent arcs of the
United States in these respects.
Since about 1900 practically all of the reconnoissance and signal build¬
ing has been in the hands of one man, Signalman Jasper S. Bilby, who as
an expert along these lines probably stands unrivaled in the world to-day.
UNITED STATES STANDARD DATUM
A direct and far-reaching geodetic movement of influence, not only to
the United States, but also one of great importance to the North American
Continent, and also to the whole world, was initiated in the adoption by
the Survey (in 1901) of the United States standard datum. It placed
the geodetic work of the Survey on one datum for the correct coordina¬
tion of the geographic latitudes, longitudes, distances, and azimuths.
From the scientist's standpoint it furnished accurate correlation of data
for a study of the figure of the earth, of isostasy, and for other related
sciences.
By its adoption as the standard datum for geodetic operations in
Canada and Mexico, it became a matter of international importance, and
consequently its designation was changed by the Survey in 1913 to that
of the " North American datum." Plans are now under way for carrying
the primary triangulation of the United States and Canada to the Yukon,
and the prediction is here made that eventually the 50 miles which sepa¬
rate Alaska from Siberia will be spanned and a junction be effected with
the great systems of Asia, Europe, and Africa. Then, with the extension
from Mexico through Central and South America, the data will be avail¬
able for a " world datum," and the final word will have been said in the
geodetic work of the earth.
BASE-LINE MEASUREMENTS
Closely related to, and forming an integral part of the triangulation
executed by the Coast and Geodetic Survey, is the measurement of the
base lines for controlling the lengths in triangulation. In this work the
Survey has furnished much of interest and of value to the geodesist.
Ever has it kept keenly before it the necessity for refined measurements,
and many valuable devices to accomplish this desired result have been
added by members of the force.
BASE BARS
The Duplex bars, invented by Assistant William Eimbeck and con¬
structed by E. G. Fischer, are probably the best form of base bars ever
devised, and gave a very high degree of precision; but they were soon
replaced by the tape as a form of base apparatus.
7
The only bar used in the United States, and probably in the world,
which gives entire satisfaction, so far as accuracy is concerned, is the
iced bar, designed by President R. S. Woodward, of the Carnegie Insti¬
tution, when an assistant in the Survey. Owing to the great cost per
kilometer of base of using this form of apparatus for field work, when
compared with the cost of using tapes, the iced bar is now used only for
standardizing other apparatus, and for this purpose it remains unexcelled.
steel Tapes
In the Coast and Geodetic Survey the tape has supplanted the other
forms of base apparatus. Credit for the introduction of steel wires and
tapes for this purpose must be given to Professor Jaderin, of Sweden, but
it was the accurate and extensive investigations made by Assistant Wood¬
ward in 1891 which caused the adoption of tapes by the Survey. He
proved that steel tapes, when used at night, and standarized under the
same conditions that prevail during the base measures, gave essentially
the same high degree of accuracy as the bars, with about one-third of
the cost and with far greater rapidity. It is practically certain that no
more base lines will be measured by base bars, at least in the United
States, except when it is necessary to standardize the tapes.
The remarkable measurement of nine base lines in one season, in 1900,
by a single party, constitutes a noteworthy achievement. The nine
bases had a total length of 43 miles and furnished a control of over 1,000
miles of triangulation. In order to eliminate constant errors, five
different sets of apparatus were used, and an average accuracy corre¬
sponding to a probable error of 1 part in 1 ,200,000 was secured. With
this work a new epoch in base-line measurement was introduced, for it
proved, through the most rigid of tests, that the tape had no superior
for speed, economy, and ease of manipulation.
invar tapes
In the use of invar tapes base measuring took another long step for¬
ward. Many severe tests have fully proved their excellence. They are
found to possess practically all of the good features of the steel tapes
but have the added advantage that they enable bases to be measured
in the daytime and even on sunny days, a fact due to the small coefficient
of expansion of invar, which is only about one-thirtieth that of the steel.
Recently the plan has been adopted of having the bases measured by
the triangulation party. By it base measurement has become simply
an incident to the triangulation, and the cost has been reduced to about
$60 per kilometer, a sum which is in great contrast to about $300 per
kilometer with the Duplex bars.
precise leveling
Practically all of the great nations of the earth have been actively
engaged upon the difficult problem of determining the correct elevation
8
of points far from their coast. It is a work which demands the highest
degree of accurate observing and painstaking endeavor. It calls for
especially designed instruments and methods of observation. These
accurate elevations are needed for the reduction of base lines to mean
sea level, for engineering operations of wide extent, and for the solution
of scientific problems concerning gravity, the tides, and other work.
In this leveling of precision the Coast and Geodetic Survey has added
much to the world's work by attainments in field operations, methods of
reduction, and scientific study of errors involved. In its great precise
level net (greater than that of any other nation) there are more than
13,000 bench marks, of which the elevations have all been accurately
fixed through a single least square adjustment of more than 80 circuits
with a total length of more than 33,000 miles.
COAST AND GEODETIC SURVEY LEVEL
Among the instruments of precision employed by the nations for pre¬
cise level work it may be truly said that none holds a higher rank than the
type which has been in use in the Coast and Geodetic Survey since 1900.
This level was designed and built within the Survey by E. G. Fischer,
chief of the instrument division, and after more than 15 years of con¬
stant service in all parts of the United States has shown itself to be,
indeed, a superior instrument for accurate and rapid leveling.
Before the introduction of this level the average rate of progress was
less than 60 miles a month. Recent work, which is of much higher
grade of accuracy, shows an average of about 100 miles, and one observer
with a party of six men recently completed 148 miles of progress, or
more than 300 miles of single line in one month. This constitutes a
world record.
Although precise leveling has been brought to the highest" perfection
in France, the work of the Coast and Geodetic Survey, by the very
magnitude of the operations, by the instruments employed, and by the
economy in speed and cost is certainly without an equal in the geodetic
world.
ASTRONOMIC INSTRUMENTS AND DETERMINATIONS
Considering astronomy as a definite part of its geodetic functions, the
Survey by its inventions and improvements may justly claim to have
demonstrated the superiority of the American methods for the deter¬
minations of terrestrial latitudes and longitudes and has secured their
adoption in the practice of every great nation in the world by the incon-
testible superiority proved for them.
The credit for the discovery of the differential method for the deter¬
mination of latitude with the zenith telescope, despite a reference to the
principle by the Danish astronomer Horrebow in the early part of the
eighteenth century, is due to Captain Andrew Talcott, United States Corps
9
1
of Engineers, who first employed it in 1834 and 1835, in the survey of the
boundary line between Ohio and Michigan. But the introduction of this
admirable method to its present world-wide use is due in a great measure
to the wise appreciation of Superintendent Bache, who almost with his
induction into office recognized its great importance and initiated the
developments which inspired the following tribute from the famous
astronomer Gould: " To Bache we owe the recognition and adoption of
this transcendent method and to him also those refinements of process
and improvements of apparatus by which alone its accuracy is rendered
possible."
The distinction due for the discovery and introduction of the method
now exclusively used for the determinations of longitudes is even more
singularly an honor appropriate to the Survey, which, within a few
months after the successful opening of Morse's first telegraph line, began
the experiments for an application of its use to longitude determinations
with such success that no change in principle has been found necessary
in the methods perfected by Bache and his assistants. Thus, the present
universally employed methods for exact determinations of the earth's
most important geographic coordinates have been suggested and per¬
fected by American genius. To the work executed by the other civilized
nations of the world the Survey has contributed many hundreds of astro¬
nomic latitudes, longitudes, and azimuth determinations, principally at
stations connected with the great triangulation system. Methods of
observing and computing have been standardized with a decided im¬
provement in speed and economy and with a most satisfactory increase
in the annual amount of work executed.
Since about 1904 all of the primary azimuths, in so far as was practi¬
cable, have been observed by the triangulation party during the progress
of the work. It is believed that this plan gives the highest degree of
accuracy, for the measurements are made under exactly the same con¬
ditions as the triangulation with which they are concerned, and the cost
is very materially reduced.
telegraphic longitudes
The formation of the great telegraphic longitude net of the Coast and
Geodetic Survey is a geodetic feat worthy of special note. No less than
five trans-Atlantic determinations have been made which serve to con¬
nect the longitudes of the United States with Greenwich and Paris, and
more than 200 stations are included in the net which covers this country.
Finally, through a trans-Pacific determination made by the Survey,
supplemented by a similar one made by Canada, the last link in the
telegraphic longitude circuit of the globe was completed, and thus nearly
all of the longitude observations made in the world are united into one
great single system, accurately correlated through this circuit.
10
TRANSIT MICROMETER
Among improvements made by the Survey to the instrumental equip¬
ment used in field astronomic work another of recent introduction
deserves mention. This is the transit micrometer used in determination
of time by stars at meridian passage. Although the transit micrometer
had been in use at fixed observatories, it was not until the investigations
made at the Coast and Geodetic Survey in 1904 that its adaptability to
portable transits was thoroughly proved. The many tests it has had in
actual field work have shown for it many features of excellence. With
its use the relative personal equation between two observers is so small
as to be masked by the accidental errors of observation and is certainly
not more than one-tenth as large as the average, using the key. No
interchange of observers is necessary, and the time of the determination
of a difference of longitude is about one-half the time taken by the older
method.
FIGURE OF THE EARTII
The very important problem of determining the shape and size of the
earth is probably the climax, from the scientific point of view, in the
geodetic work of the Survey.
Reference has already been made to the use of the arcs of triangulation.
in determining the figure of the earth. When many arcs, both merid¬
ional and latitudinal, are all joined together on the same trigonometric
and astronomic basis, the area method, developed in the Coast and
Geodetic Survey since about 1901, is without doubt far superior to the
arc method. In it are all of the features of the arc method, to which
many important new features are added. Using the great system of
triangulation in the United States to furnish the area factor and the many
astronomical measures connected with the system to furnish the curva¬
ture factors, a value for the figure of the earth was derived which is of a
very high degree of accuracy. The investigations and results obtained
in this work are noteworthy contributions to geodesy. Some of the
prominent features of this investigation are shown in the wide area
treated, the large number of astronomic observations involved, and the
unusual methods of computation used. Topographic irregularities within
4,000 kilometers of each astronomic station were considered, and account
was taken of possible distribution of density beneath the surface of the
earth. These features, together with the actual results obtained, make
this a monumental work.
By a study of the station errors, or deflections in the verticals, which
were developed when the astronomical and geodetic determinations were
compared, evidence was brought forth which established the fact that
the condition of isostasy exists in the earth, a fact which is of interest
and value to geodesy and geology.
11
These studies of the figure of the earth and isostasy have attracted the
attention of the scientific world. Doctor Woodward, the distinguished
geodesist, is authority for the statement that the work done by the Coast
and Geodetic Survey on isostasy is the greatest contribution to geodesy
since the time of Gauss and Bessel.
GRAVITY MEASURES
Another method of attacking this important problem of the earth's
shape and size is by the use of the pendulum in the determination of
gravity. The contributions of the Coast and Geodetic Survey to this
field of geodesy are given in the results of more than 30 foreign stations
and of 219 stations in the United States.
Happily the gravity conference held in 1882 indorsed the plan of using
the invariable pendulum and of employing the differential method of
carrying on gravity work, and the Survey's present excellent equipment
and methods are the direct results. In its present type of apparatus,
known as the Mendenhall pendulums, the Survey has a form which for
compactness, portability, precision, and ease of operation ranks well
among the best in this field of endeavor.
Two features in recent gravity work are worthy of note. One is the
application of the interferometer to the measurement of the flexure of
the pendulum support, thus giving a direct measurement of this small
quantity in terms of a wave length of light. It is believed that the result¬
ing corrections to the period of the pendulum are more accurate than those
by the older static method where the corrections were derived under
exaggerated conditions. The interferometer has been in use for about
eight years as a field instrument, and determinations of the flexure have
been made at about 140 gravity stations, through a very wide range of
conditions in piers and external vibrations.
The second feature worthy of note in recent gravity work is the
deriving of the rate of the chronometers from time signals at noon, sent
from the Naval Observatory over the lines of the Western Union and
Postal Telegraph companies, a distinct advantage over the older method.
By it the local time observations are dispensed with, the time of occupa¬
tion of a station is decreased, and the labor of preparing the station greatly
lessened, all of which contribute to a lowering of the cost per station occu¬
pied. In connection with this it is interesting to note that Assistant
Schott in 1882 made the statement that "time furnished telegraphically
by an observatory whose clock is protected from changes of tempera¬
ture and pressure will be preferable to any local determination at a field
station."
FIELD AND OFFICE FORCE
Uittle has been said of the men who have composed and do now com¬
pose the field and office force of the Coast and Geodetic Survey. What
12
the Survey is and accomplishes is due to these men, and to the spirit
which influences them. To them must be given the credit for much that
the Survey has contributed to geodesy. It would be difficult to find a
body of men of greater enthusiasm for, or a higher scientific attitude
toward, their work. They have a careful devotion to duty and an interest
in the success of the Survey and its work, a fact which has developed a
corps of workers of unrivaled excellence.
They have ever been most alert to adapt new discoveries, made in the
various fields of science, to the needs of the Survey, and to plan new and
improved instruments; while to the theoretical work of geodesy they
have added much by critical discussion and extensive study of results.
Workers must have tools, and this fine body of skilled observers would
be seriously handicapped in their work if suitable equipment were not
furnished them. The Survey is particularly fortunate in having a body
of skilled artisans in the instrument division, under the supervision of a
most highly efficient officer. In the division there have been designed or
built nearly all of the instruments of precision which have helped so mate¬
rially to place the Coast and Geodetic Survey in its present high position.
Of the relation of the geodetic work of the Survey to that of the world,
as shown by its share in the operations of the International Geodetic
Conference, only slight reference is here made, for this subject is dealt
with in an address by former Superintendent O. H. Tittmann, who is
much more capable of presenting this subject.
In the foregoing the endeavor has been made to give some idea of the
contributions which the Coast and Geodetic Survey has made to geodesy.
Of necessity much has been omitted, but what has been given will bear
witness that the world's geodesy has been greatly enriched by the work
of the Survey.
A test of the greatness of the geodetic work of the Survey may be had
in a review of the comments made by prominent men in other organiza¬
tions and countries, by men who are well qualified to judge. They all
accord to the geodetic work of the Survey a very high place in the geodesy
of the world. One comment only will be here given as a fitting close to
this brief review of the contributions made by the Coast and Geodetic
Survey to geodesy.
Commandant Perrier, the French geodesist, in speaking of the work of
the Survey says:
There is no example in the history of geodesy of a comparable collection of measure¬
ments, made with so much determination, such rapidity, and such powerful means of
action, and guided by such an exact comprehension of the end to be attained.
o