APPLICATION OP THE ELECTRIC TELEGRAPH. 331 



of longitude. The observatories at Cambridge, New 

 York and Philadelphia, were all put in communication 

 with each other, and with "Washington city. The clock 

 which was to be employed was set up in Philadelphia, 

 and connected with the telegraph line. Simultaneously 

 with the beats of this clock, a click was heard of the 

 magnets at Cambridge, New York and Washington. 

 The paper being allowed to run off from the reel, it was 

 graduated into parts corresponding to the beats of the 

 Philadelphia clock. The astronomer at Cambridge now 

 selects a convenient star for observation, and announces 

 it by name to each of the other stations. He strikes the 

 key of his register as the star passes successively each 

 wire of his transit instrument, and the dates are printed 

 not only upon his own roll of paper, but also upon those 

 at New York, Philadelphia and Washington. When 

 the same star comes over the merfcian of New York, 

 the observer there goes through the same operation, and 

 his observations are printed upon all four of the papers. 

 The Philadelphia observer does the same when the star 

 comes upon his own meridian. Thus we have four Jong 

 rolls of paper, one at Cambridge, a second at New York, 

 a third at Philadelphia, and a fourth at Washington, all 

 graduated into equal parts by the ticking of the Phila- 

 delphia clock, and upon these we have printed the 

 instants at which the star was seen to pass each wire of 

 the transits at Cambridge, New York and Philadelphia. 

 The position of each mark thus printed shows not only 

 the second of occurrence, but also the fraction of a 



