APPLICATION OF THE ELECTRIC TELEGRAPH. 333 



essary for him to move his fingers at the instant the 

 star is seen to pass each wire of his telescope, and his 

 observation is recorded in a permanent form, and may 

 be subsequently examined at his leisure. 



During the months of July and August, 1849, a tele- 

 graphic comparison was made between the observa- 

 tories of Philadelphia, and Hudson, Ohio. Signals were 

 exchanged on three different nights, the results of which 

 gave the difference of longitude between the High School 

 observatory, and the Hudson observatory 25m. 5*7s. 

 During the same summer, some new comparisons were 

 made between Philadelphia and Washington. 



On the 5th of February, 1850, a perfect telegraph con- 

 nection was made between "Washington and Charleston, 

 South Carolina. The thermometer at Washington was 

 10 Fahrenheit, and at Charleston 28 Fah., and the in- 

 sulation of the wires was excellent. Professor Lewis E. 

 Gibbes was in charge of the operations at Charleston, and 

 the operations at Washington were conducted by S. C. 

 Walker. The times of transit of a full series of zenith 

 stars were telegraphed between Professor Gibbes's observ 

 atory and Washington, and recorded on the register at 

 each station. The instruments were all well adjusted, and 

 all necessary precautions taken to insure satisfactory re- 

 sults. Signals were also exchanged on the llth and 

 12th of February, but the results were not so satisfactory 

 as those of the 5th. The result of these comparisons in- 

 dicates that Charleston is llm. 45'27s. west of Wash- 

 ington. 



