of Longitude hy means of the Electric Telegraph. 339 



telegraph. Morse's magnetic telegraph has been in operation 

 between these places for a considerable time, and Prof. Bache 

 proposed to use the line for the transmission of signals for the 

 comparison of our local times for the use of the coast survey. 

 Accordingly I erected a temporary observatory last season as 

 near to this city as I conveniently could, and set up a transit 

 instrument and clock. A wire was then carried from my ob- 

 servatory to the telegraph-office, thus connecting me with the 

 regular Philadelphia line. A wire was also carried from the 

 Philadelphia telegraph-office to the High School Observatory 

 in Philadelphia, and another wire was carried from the Wash- 

 ington telegraph-office to the National Observatory. Thus 

 three observatories, at New York, Philadelphia, and Wash- 

 ington, were in telegraphic communication ; and having de- 

 termined our local times by astronomical observations, we 

 only needed some signal which could be heard simultaneously 

 at the three places. This signal was affiarded by the click of 

 a magnet in the usual mode of telegraphic communication. 

 Our plan of operation is as follows : — At ten in the evening, 

 when the usual business of the telegraph company is concluded, 

 our three observatories are put in communication with each 

 other. After corresponding with each other long enough to 

 ascertain that everything is in good order. New York com- 

 mences giving clock signals. At the commencement of a 

 minute by my clock I strike the key of my register, and a click 

 is heard simultaneously at New York, Philadelphia, and 

 Washington. The three observers record the time each by 

 his own clock. At the expiration of 10^ I give a similar sig- 

 nal, and all three record; after another 10® I do the same, 

 and so on to twenty signals. Having waited one minute, 

 Philadelphia repeats the same series of signals, and all record 

 the time. We then wait another minute, and Washington 

 repeats the same signals. Thus we have obtained sixty com- 

 parisons of our clocks, which will give our difference of lon- 

 gitude with as great accuracy as we can determine our local 

 times. 



In our first experiments we met with a great many disap- 

 pointments, as might have been anticipated from the novelty 

 and delicacy of the undertaking ; but we have triumphed 

 over them all. Onjive different nights we have transmitted 

 good signals back and forth, and we propose to continue the 

 comparisons until a further degree of accuracy is not to be 

 expected. The errors of our clocks have not yet been rigo- 

 rously computed, and we have not obtained final results ; but 

 we have made sufficient comparisons to know that the results 

 of different nights agree remarkably well with each other. I 



Z2 



