" 



SECTION IV. 



APPLICATION OF THE ELECTRIC TELEGRAPH TO ASTRO- 

 NOMICAL USES. 



IN 1839, Professor Morse suggested to M. Arago, that 

 the electric telegraph would afford the means of determin- 

 ing the difference of longitude between distant places with 

 an accuracy hitherto unattainable. 



The first practical application of this method was made 

 by Captain Charles Wilkes, in June, 1844, between 

 Washington and Baltimore.* Captain Wilkes conducted 

 the experiments at "Washington, and Lieutenant Eld at 

 Baltimore. Two chronometers, previously rated by as- 

 tronomical observations in the vicinity, were brought to 

 the two telegraph offices, and were compared together 

 through the medium of the ear, without coincidence of 

 beats. The comparisons of the chronometers were con- 

 tinued for three days, and the results indicated that the 

 Battle Monument at Baltimore was 1m. 34*87s. east of 

 the Capitol. This method will furnish differences of 

 longitude with a precision greater than any method 

 hitherto practiced; but it is susceptible of great im- 

 provements. 



* Vail's American Electro-Magnetic Telegraph, page 60. 



