62 . Mr, G. V.Bonii on the application of Electro-magnetism 



th^' I'fecorda of that department, the following abstract of the 

 history of an invention recently brought into use in America, 

 by which electro-magnetism is introduced as an agent in the 

 determination of differences of terrestrial longitude, and for 

 various astronomical purposes in which the exact noting of time 

 enters as an important element. 



On the 9th of June 1844, Capt. Charles Wilkes, U.S.N., 

 made the first experiment for detemiining longitudes by means 

 of the electric telegraph, between AVashington and Baltimore, 

 with chronometers rated at each place. All subsequent experi- 

 ments for determining longitudes by the electric telegraph in the 

 United States, have been made at the expense of the Coast Sur- 

 vey, and by its officei*s, or by their request, and uod^* their 

 immediate supervision. ^'^ iioi3L>jiii«no.> -nii .'.*tl .;ij:>bjit>iimjifi:/> 



On the 10th of October 1846, star-signals were first ex- 

 changed between the Washington Observatory and that of the 

 Central High School of Philadelphia. The outfit of telegraph 

 junction lines and apparatus was made by the Coast Survey. 

 The use of the astronomical instruments for the occasion at the 

 Washington Observatory, had been offered by Lieut. Matthew 

 F. Maury, U.S.N., superintendent. 



The experiment was made under the charge of Sears C. Wal- 

 ker, Esq., one of the assistants of the Coast Survey, who from 

 that time to the present, under an appointment from Prof. A. D. 

 Bache, LL.D., superintendent, has had uninterrupted charge of 

 this work. The apparatus used this evening was devised and 

 constructed by Joseph Saxton, Esq. The star-signals, or taps 

 on a make-circuit finger-key at the instant of the passage of a 

 star over a wire of a transit instrument, were made that night 

 by Lieut. J. J. Almy, U.S.N., and were recorded by the ear by 

 Mr. Walker and Lieut. J. M. Gillin, U.S.N., at Washington, and 

 Prof. E. O. Kendall, Dii-ector of the Philadelphia High School 

 Observatoiy at Philadelphia. 



The longitude between the two stations by this night's work 

 agrees within 0*2 second with the average of all the work done 

 since. 



On the 27th of July 1847, coincidence of beats of solar and si- 

 dereal chronometers were for the first time tried between Phila- 

 delphia and Jersey city. These coincidences were noted at each 

 place by comparison of a solar and sidereal time-keeper. The 

 circuit of the telegraph line was closed temporarily every ten 

 seconds by the astronomer at one of the stations, and the receiving 

 magnet beats were heard sensibly at the same instant of absolute 

 time at both stations. The date of coincidences of these magnet 

 beats with the stationary clock beats (the one being at solar 

 the other at sidereal time), were recorded at both stations. This 



