NATURAL PHILOSOPHY. 125 



timore. Two chronometers, previously rated by astronomical observa- 

 tions in the vicinity, were brought to the two telegraph offices, and 

 were compared together through the medium of the ear, without coin- 

 cidence of beats. This process is accurate enough for geographical or 

 nautical purposes ; but its precision stops short of the mark where the 

 requirements of geodesy begin. In fact, two clocks beating the same 

 kind of time, when placed side by side, cannot be compared together, 

 by the human ear, with sufficient precision for geodetical purposes. 

 The subsequent experience of the Coast Survey has shown, that where 

 several astronomers make independent comparisons of clocks, in this 

 manner, two seconds of arc, or twelve hundredths of a second of time, 

 is an average discrepancy between their results. 



" The subject of telegraph operations for longitude had engaged 

 the attention of the Superintendent of the Coast Survey previous to 

 the experiment of Capt. Wilkes; but the orders received by me for 

 this purpose bear date November 24, 1845. In 1846, the very first 

 season in which two astronomical stations of the Survey were brought 

 in connection by the Morse telegraph lines, the work of connecting 

 them together in longitude was commenced in earnest by the Superin- 

 tendent of the Coast Survey. The cooperation of the National Obser- 

 vatory, as one of the stations, was freely tendered by its Superintendent, 

 Lieut. Maury, U. S. N., and accepted by Prof. Bache. Another station 

 was established at Philadelphia, under the superintendence of Prof. 

 Kendall, and still another at Jersey City under Prof. Loomis. 



" Owing to the imperfect insulation of the lines, the connection of 

 Jersey City with Washington failed that year; but the Washington 

 and Philadelphia stations were connected together astronomically on 

 the 10th and 22d of October. The method of comparison by coinci- 

 dence of beats of solar and sidereal timekeepers, was not introduced 

 this year; but the equivalent one w r as employed, viz., the exchange 

 of star-signals. These are the dates of instants of the passage of a 

 star over the wires of the eye-piece of the transit instrument, signal- 

 ized by tapping on the telegraph key at one station, and recording it 

 on the Morse register at both. 



"In 1846, we connected together in longitude the Washington and 

 Philadelphia stations. In 1847, the programme left unfinished in 

 1846, by the imperfection of the lines, was resumed and completed, 

 and Washington, Philadelphia, and Jersey City were connected to- 

 gether. On the 27th July, 1847, the method of coincidence of 

 beats, used so successfully by R. T. Paine, Esq., in the chronometric 

 operations for longitude in Massachusetts, and by Struve and Airy in 

 their chronometric enterprises, was applied to the telegraphic compari- 

 sons of the Philadelphia arid Jersey City clocks. This method of 

 coincidence was used in combination with exchanges of star signals, 

 in the telegraphic operations of the Coast Survey in 1848, when the 

 Cambridge observatory, under Prof. Bond, and the Stuyvesant Station 

 in New York, were connected together by the Coast Survey. 



"In October, 1848, Cincinnati was connected with Philadelphia. 



11* 



