64 Application of Electro-Magnetism to Astronomical purposes. 



from Dr. Locke that he and his sous had completed an automa- 

 tic circuit interrupter, extended a junction- wire from the Cincin- 

 nati Telegraph Office, so as to embrace Dr. Lockers clock at his 

 house, fitted up as a circuit breaker, with a tilt hammer struck by 

 the teeth of the escapement wheel. Mr. Walker also, acting for 

 the Coast Survey, engaged the use of the line from Louisville to 

 Pittsburg, to ti-y the experiment with Dr. Locke's contrivance. 

 No astronomical nor clock-signals were exchanged this evening, 

 and no attempt was made to determine longitudes. In this 

 experiment Dr. Locke's clock graduated a fillet of paper as deli- 

 vered by the Morse register. 



In 1849, January 19th, .the first actual experiment of the 

 automatic imprint of star-signals on a time scale was made be- 

 tween Philadelphia and Cincinnati. The telegraph line from 

 Philadelphia to Cincinnati was engaged for use of the Coast 

 Survey by Mr. Walker. The automatic clock interrupter w as fur- 

 nished by Dr. Locke at Cincinnati. The star-signals were given 

 by Prof. Kendall at Philadelphia, and recorded at both places. 

 The Cincinnati Obsei-vatory, in the absence of Prof. Mitchell, 

 could not be used for the pui-pose of longitudes. 



The longitudes of Cambridge, New York and Philadelphia, were 

 determined on the 23rd of January 1849 by star-transit signals, 

 given for the same star as it passed the meridian of these three 

 stations. These signals were recorded at Washington, Phila- 

 delphia and Cambridge. The managements were under the 

 charge of Mr. Walker. The circuit-breaking clock was prepared 

 by Mr. Walker on Dr. Locke's plan, and located at Philadelphia. 

 The same clock contained a tilt-hammer interrupter for making 

 signals by the teeth of the hour-wheel every two minutes. This 

 instrument was invented in the year 1847 by J. J. Speed, Esq., 

 President of the Telegraph Company in Detroit, Michigan. 



The detection of a dday in the transmission of the galvanic 

 inducing wave proportionate to the space traversed, was made 

 by Mr. Walker immediately after examining and comparing to- 

 gether the registers of the four stations above mentioned. 



The consideration of this phsenomenon led Prof. Walker to the 

 discovery of the velocity of the galvanic w^ve. His articles on the 

 subiect have been published in the Proceedings of the American 

 Philosophical Society for March 1849, in Silliman's Journal of 

 Science, and in the Astronomische Nachrichten. A velocity of 

 15,400 miles per second is given by him as the most probable 

 result. 



In the summer of 1849, Prof. Mitchell proposed the use of a 

 revolving disc of type-metal to receive the records. Mr. Saxton's 

 plan of receiving the records upon a sheet of paper rolled upon 

 a cylinder, seems to be that which combines the most practical 



