TELEGRAPHIC DETERMINATION OF LONGITUDE. 431 



Yale College. These instruments were so constructed that the eye- 

 piece was at one end of the horizontal axis, a prism at the junction 

 of the axis and telescope-tube reflecting at a right angle the rays 

 from the object-glass, thereby enabling the observer to direct the 

 instrument upon stars of any elevation above the horizon without 

 change of position. 



The command of the expedition was given to Lieutenant-Command- 

 er F. M. Green, U. S. N., and it was intended that the work should 

 be commenced in the winter of 1873-'74 ; but the non-completion 

 of the instruments and the probability of trouble resulting from the 

 Cuban outrages interfered with this plan, and the Fortune was tem- 

 porarily employed as a tender to the squadron at Key West. 



Upon the dispersion of the assembled squadron in Ajjril, 1874, 

 Lieutenant-Commander Green was directed to complete a survey of 

 the Mexican Gulf coast, commenced by the United States steamship 

 Wyoming. This work employed the time till the following August, 

 when the Fortune returned to Washington, and was at once refitted 

 for the prosecution of the original design. 



Fortunately for the success of the work, the services of Mr. Miles 

 Rock, formerly of the observatory at Cordova, were secured as prin- 

 cipal astronomical assistant; and the Fortune sailed on the 24tli of 

 November, 1874, from Hampton Roads for Jamaica. 



Upon arrival at Kingston, definite arrangements were made witli 

 the manager of the telegraph cables, the gratuitous use of which had 

 been ofliered very promptly and courteously by the London board of 

 directors. 



As it had been decided to commence the work by measuring be- 

 tween Panama and Aspinvvall, the Fortune sailed for the latter i)lace 

 on the 9th of December, arriving on the 12th. 



Portable observatories had been constructed, to shelter the instru- 

 ments and observers, and were immediately set up at Panama and 

 Aspinwall upon obtaining permission from the local authorities. 



Throughout the work the same general system was pursued, and 

 was briefly as follows: As soon as practicable after the establishment 

 of a party at each station, the work was commenced by observing 

 stars on five clear nio-hts, from 8 to 10 p. M., and from 11 p. m. to 1 a. m. 

 for determining the errors of the chronometers, and during the hour 

 from 10 till 11 p.m. exchanging time-signals between the two stations. 

 This was effected as follows : 



Telegraphic communication being established betw^een the obser- 

 vatories, the senior observer sent a preparatory signal at ten seconds 

 before the completion of a minute by tapping his key several times in 

 quick succession ; then exactly at the even minute, pressing his key 

 again for about a quarter of a second, and repeating this signal at 

 intervals of five seconds till the completion of the next even minute. 

 The hour and minute when the first signal was sent were then tele- 



