THE TRANSATLANTIC LONGITUDE. 3 



II. 



PREVIOUS DETERMINATIONS OF THE TRANSATLANTIC LONGITUDE. 



The several determinations of longitude between European and American sta- 

 tions, which have hitherto served as the basis for astronomical and nautical 

 computations, may be classified under the three heads — from moon-culminations, 

 from eclipses and occultations, and from chronometers. Most of them have been 

 referred to one or the other of two American points, the College Observatory at Cam- 

 bridge, and the Naval Observatory at Washington. The former has presented 

 especial conveniences for the chronometric expeditions, both from its close vicinity to 

 the point of landing and shipment in Boston, and from the charge of these expedi- 

 tions being confided to the director of the observatory, who was specially versed in 

 chronometric matters, and whose ofiice in Boston was connected with the Cambridge 

 clock by a telegraph wire, so that not even the transportation to the observatory 

 was requisite. The latter, as situated at the national capital, and administered by 

 one of the departments of government, has been naturally selected, in most cases 

 during recent years, as the fundamental point for other determinations. As the 

 European point of reference, Greenwich has been employed in all cases. 



The telegraphic longitudes of the Coast Survey have, since the first year, been 

 uniformly referred to a third American point, the " Seaton Station" of the Coast 

 Survey in the city of Washington. But the longitudes of New York and Philadel- 

 phia, upon which that of Cambridge depends, were referred to the Washington 

 Observatory, which is situated^ 12'.44 westward from the Seaton Station, by geo- 

 detic measurement. The longitude between Cambridge and Washington, as deter- 

 mined by my predecessor, Mr. Walker, in 1848 and 1849,^ is as follows : — 



Cambridge east from Mr. Rutherfurd's Observatory, New York . 0'' 11" 26'.07 

 Mr. Rutherfurd's east from Jersey City Station (geodetic) . . 11.93 



Jersey City Station east from Washington . . . . ' . 12 3.54 



Cambridge (dome) east from Washington . . . . . 23 41.54 



and this value has since that time been adopted in all computations, and in the 

 standard books of reference. It must be very near the truth ; yet it depends in 

 part upon a geodetic measurement across the Hudson River, where no telegraph 

 wire then existed, and was the earliest determination by the new method, before 

 the employment of many refinements and precautions since introduced. Moreover, 

 the portion between Jersey City and Washington was deduced from the simple 

 telegraphic comparison of clocks — a method which repeated experience, as well as 

 theory, shows to be entirely inferior in precision to the Coast Survey method of star- 

 signals. For this reason, I have more than once urged a redetermination of the only 

 weak link in our chain of telegraphic longitudes, by connecting 'Mr. Rutherfurd's 

 observatory at New York with the Seaton Station, as well as the Washington 



' Value determined since that given in the Coast Survey Report, 1851, p. 322. 

 » Coast Survey Report, 1848, p. 22 ; 1849, pp. 19, 20, 31. 



