310 HISTORY OF ASTRONOMY. 



For the distance of 250 miles embraced in these ex- 

 periments, the electric current took no sensible time to 

 propagate itself, and it appeared that two clocks at this 

 distance could be compared with the same degree of 

 precision as if they were placed side by side. 



During the summer of 1848, similar experiments were 

 made to determine the difference of longitude between 

 New York and Cambridge. A wire was extended from 

 the Cambridge observatory, to connect with the New 

 York and Boston line near Brighton ; and another wire 

 was carried from the same line to Mr. Kutherford's ob- 

 servatory in the upper part of New York city. Thus 

 the observatories at New York and Cambridge were 

 put in telegraphic communication. At New York a 

 new forty-five inch transit instrument, by Simms, of 

 London, belonging to the Coast Survey, was used for 

 local time, and a sidereal clock with chronometers for 

 comparison. At Cambridge a similar transit was used, 

 with numerous chronometers carefully compared. The 

 observations at Cambridge were made by Professor 

 W. C. Bond, and those at New York by Professor 

 E. Loomis. The comparisons of time were made both 

 by the method of coincidences already explained, and 

 by telegraphing the transit of the same star over both 

 meridians. The latter method was practiced in the fol- 

 lowing manner: c 



A list of zenith stars is selected beforehand, and 

 furnished to each observer. When every thing is pre- 

 pared for observation, the Cambridge astronomer points 



