SEARS COOK WALKER. 43! 



In 1845 Mr. Walker's affairs underwent a revolution. Certain 

 commercial operations turned out disastrously and entirely be- 

 reft him of means. The sense of defeat, the loss of luxuries at 

 a time of life when habits have become fixed, together with 

 anxiety for the future, made the blow a hard one. But it re- 

 vealed to him, and to the world, the extent of his own scientific 

 ability, and opened the way to higher intellectual gratifications, 

 which he quickly learned to appreciate. The Secretary of the 

 Navy offered him a position in the observatory at Washington, 

 which he at once accepted. Here, for the first time, the 

 facilities which his special gifts required were at his disposal, 

 and he immediately proceeded to make good use of them. 

 After a short time he gave up his position at the observatory 

 to accept the direction of the longitude department of the 

 Coast Survey an office which he ably filled until his last 

 illness. 



Early in 1847, while engaged in researches upon the then 

 newly discovered planet Neptune, he became convinced that a 

 star observed by Lalande in May, 1795, must have been this 

 planet. With the telescope of the Naval Observatory Prof. 

 Hubbard confirmed this conjecture, and astronomers were 

 thus furnished with an observation of Neptune made fifty- 

 two years before, which afforded means for a most accurate 

 determination of the planet's orbit. The American was none 

 too soon to secure priority, for, quite independently, the same 

 important fact was laboriously hunted down in Europe by 

 Petersen only a few weeks later. Walker now attacked the 

 problem of Neptune's orbit ; Benjamin Peirce was at the same 

 time calculating the planet's perturbations. The approximate 

 results of each furthered the computations of the other, so that 

 within eighteen months from the discovery of the planet these 

 two Americans had attained a remarkably accurate statement 

 of its theory. 



In conjunction with Prof. A. D. Bache, Superintendent of 

 the Coast Survey, Walker developed the method of determin- 

 ing differences of longitude by telegraph. One feature in- 

 troduced by Walker was the application of the method of coin- 

 cidence of beats to the comparison of timekeepers one indi- 

 cating mean, the other sidereal time at the two ends of a 

 telegraphic line. These beats were signalled from one station 

 to the other by taps of an observer upon the telegraph key. 



