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You say I 'm a fool ;
“ Montes, prados, flores, selvas,
Consolad á un afligido ;
"Dicen algunos que son
Los zelos de amor un hielo ;
ART. VIII. — Letter from the Secretary of the Treasury,
transmitting a Report of F. N. HASSLER, Superintendent of the Coast Survey, showing the Progress made therein up to the Present Time. Doc. No. 28. House of Representatives. Treasury Department. 27th Congress, 2nd Session.
By this valuable communication, as well as by information reaching us from various sources, we are warned that the great public work of the Survey of the Coast is in danger of being again abandoned, or, what we should regard as still more unfortunate, of being superseded by some other plan of operations.
In a former Number* we presented a concise view of the
* See North American Review, Vol. XLII. pp. 75 et seq.
It is our
nature of geodesical operations, and of the principles upon which they are based. The remarks there made
the subject we conceived were sufficient to show the futility of any scheme for arriving at the perfect knowledge of any extensive portion of the earth's surface, for constructing a map, or correctly determining and connecting a number of distant situations, by any other rules of procedure than those which the science of Geodesia prescribes. They also afforded some data for a comparison between the American survey, as far as it had then proceeded, and similar works in Europe; such as, whether applied to the progress or the character of the work, might well gratisy national pride. Our present purpose is, to submit a few remarks, noi of a character to interest the scientific reader, but designed rather to arrest the attention of men, who, being necessarily uninformed upon matters of strict science, are nevertheless called upon in their high places to exercise judgment, and exert authority, upon questions in which the highest science is involved. present aim to secure a clear and impartial investigation ; to correct misrepresentations ; to counteract the designs of scheming speculators ; to defeat, if necessary, the instigations of ill-will; and to uphold the scientific reputation of the country, which is in some measure dependent upon the successful prosecution of this great national undertaking.
The question first in importance with regard to the coast survey is, whether any other mode can be adopted ; - this mode having for its object the greatest amount of useful information, in the shortest time, and at the least expense. In discussing this question, so much has been said, and is still urged, concerning the use of chronometers, and the substitution of them for the present system of triangulation, that it seems worth while to say a word upon this subject, premising, that the serious consideration we here give to it does not arise from any idea of the value attached to such a suggestion in the minds of scientific men.
The chronometer in the hands of modern artists bas, it is true, attained a degree of excellence which admirably adapts it to the general purposes of navigation, and supplies to seamen the most useful means of solving the problem of longitude. . Still it is far too imperfect an instrument to be relied on implicitly. It possesses an inherent and constant liability to error, and although its accuracy may be preserved through
any short period, this liability is so multiplied by time, and the chances of accident, as to deprive even those which are most carefully constructed of all claim to perfect confidence. In cases where their use is indispensable, as in detached and local surveys, in the cursory examination of distant and inhospitable regions, or in carrying a chain of longitudes around the globe, and generally where strict and careful measurement is for any reason forbidden, their imperfection is in some measure remedied by numbers. Acting as checks upon each other, the amount of error is reduced, and the observer is enabled to fix, with a degree of precision sufficient for the security of ordinary navigation, the simple position of certain points and headlands. This, however, is regarded only as the palliation of an evil; the evil itself is fundamental, and admits of no complete remedy.
In determining differences of time between meridians widely separated, chronometers have sometimes proved remarkably successful, and have exhibited results of surprising accuracy. The reverse of this proves to be the case in the adjustment of minor differences, where the essential defects of the instrument are particularly displayed. There is no space, however small, of perceptible magnitude, which may not be submitted to trigonometrical measurement; but it will be readily understood, that there are points, at minute distances asunder, between which no difference of local time can be estimated. If it be asserted, which we are by no means prepared to admit, that such distances are unimportant in a geographical view, it will appear that they are of the highest topographical value when we come to consider the character of our southern coast.
If chronometers, however, could be implicitly relied on, and the determination of longitudes by means of them admitted of greater exactness, still it is to be borne in mind that their use, in connexion with the sextant, goes so far only, as to decide a certain number of fixed points.
This cannot in any strictness of language be called a survey. It still remains to fill up the intermediate spaces by some sort of measurement, and the mode and result of this operation are questions of serious importance. We need not enter into any detail to show, that a survey of this kind must content itself with the bare outline of coast, harbours, islands, &c., neglecting all the valuable details belonging to
physical and statistical geography, differences of level, and ibe distribution, limits, and peculiarities of the country under inspection, all of which are included in the operations of a geodesical survey.
We are told, that despatch is one of the recommendations of the chronometric plan. Numerous parties will probably, therefore, be immediately employed, and it will remain afterwards to harmonize their labors by joining the distant points of observation. To do this will, we conceive, be no easy task ; and, if such a plan be adopted, we shall not be astonished to learn hereafter, that the attempted meeting of these unconnected operations is likely to break up in the most admired disorder.
We do not mean, in any thing we have said, to underrate the value of chronometers in their legitimate sphere. They might, undoubtedly, be advantageously employed in the preliminary determination of important points on the coast, which are known to be erroneously laid down.
Their accuracy may be depended upon within a mile, and even this imperfect knowledge will be in some degree a relief to navigators, where errors of alarming and uncertain magnitude are known to exist in their charts. Mr. Hassler has, in his letter to Mr. Gallatin, given to this proposition all the consideration it merits. * If such occasional use should be made of them, and the present system of survey should be continued, subsequent comparisons will abundantly prove, that even the simple determination of geographical positions by chronometers (omitting all question of a connected survey), however skilfully and expensively conducted, is unavoidably defective.
In a matter that may be subjected to rigid mathematical investigation, results are anticipated, and conclusions distinctly enunciated. But perhaps it will enforce our argument to exhibit some facts, that have immediate relation to the present inquiry. We select such as are nearest at hand. An attempt was made to determine the place of the Capitol, by means of chronometers, by Mr. Paine of Massachusetts, a gentleman distinguished for his zeal and ability in these calculations. He carried three chronometers from Boston to Washington, through Philadelphia, and back, observing the difference of
* American Philosophical Transactions, New Series. Vol. II. pp. 238, 239.
meridians of the three cities, both going and returning. The results of these are spoken of as important. The difference of his two longitudes of Washington, by Philadelphia and by Boston, is 14."25. The difference between the mean of his observations, and the adopted longitude of Washington is 12."9 ; whilst Mr. Paine's longitude of Washington differs from the mean of seven results of astronomical observations, solar eclipses, and occultations, by 41."4.*
In the trigonometrical survey of the State of Massachusetts, begun in 1831, and concluded about a year since, embracing a territory of 8230 square miles, we find an exemplification of our argument at once pertinent and conclusive.
A letter from Mr. Simeon Borden, the superintendent of this survey, to the American Philosophical Society, in addition to an account of the work, gives a comparison of his own results with those obtained by Robert Treat Paine, Esquire, from observations with a Troughton's sextant and mercurial horizon, and chronometers transported to different stations."
In the longitude of Pittsfield the chronometers exhibit a difference of 23."98, — nearly one half of a mile ; yet thirtynine chronometers were used in thirteen.journeys. The meridians of Cambridge and Dedbam are 3.'30."43 apart by trigonometrical measurement; the chronometers give the difference of longitude 3.'11."10, making an error of 19."33. In the case of Cambridge, twenty chronometers were used in six journeys, and in that of Dedham iwenty-three chronometers in seven journeys. Gloucester and Plymouth, both seaport towns, which ought therefore to be known correctly, coincide in longitude, within 2."10. The chronometers have increased that difference to 8."55. This instance illustrates what we have before said of the incapacity of chronometers to note minute differences of local time with the requisite accuracy.
Williamstown, where twenty-eight chronometers were employed in ten journeys, is placed 19."24 to the west of its true position. We have already remarked, that Pittsfield is 28."98 in error. The sum of these two variations is 43."22, or eight tenths of a mile, and one third nearly of the difference of longitude of the two places.
* Determination of the Longitude of several Stations, &c. reported by Sears C. Walker. See American Philosophical Transactions, Vol. VI. p. 265, note.