312 HISTORY OF ASTRONOMY. 



were practiced, during which time 12,000 signals were 

 exchanged between the observatories at New York and 

 Cambridge. 



The personal equations for the clock corrections of the 

 different observers were obtained by a very extensive 

 series of comparisons, 894 in number, the transit of the 

 same star over alternate wires of the telescope being 

 noted by different observers. 



The result of all the comparisons gave the difference 

 of longitude between Cambridge and Mr. Kutherford's 

 observatory, 11 minutes and 26.07 seconds. 



During the month of October, 1848, the difference of 

 longitude between the Cincinnati observatory and the 

 High School observatory in Philadelphia was also de- 

 termined by telegraph for the use of the United States 

 Coast Survey. A wire was carried from the Cincinnati 

 observatory to the Philadelphia line, thus putting the 

 observatories of Philadelphia and Cincinnati in tele- 

 graphic communication. The series of observations here 

 made was substantially the same as had been practiced 

 two months before between New York and Cambridge. 

 A sidereal clock in Philadelphia was compared with a 

 solar chronometer in Cincinnati, by beating seconds upon 

 the key of the telegraph register for fifteen minutes, and 

 noting the instants of coincident beats. Transits of the 

 same stars over both meridians were also telegraphed, 

 as had been practiced between Cambridge and New 

 York. These comparisons were made on six differ- 

 ent nights, and gave the difference of longitude be- 



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