120 THE POPULAR SCIENCE MONTHLY. 



no telegraphic operation for longitude, and of no step in the im- 

 provement or perfectionment of the art, in Europe or America, 

 which has not been the work of the officers proper of the Coast 

 Survey, or of commissioned officers and civilians acting tempora- 

 rily as assistants. . . . I will not here allude to the respective claims 

 of Americans for priority or superior excellence of inventions 

 and suggestions, believing that it will be becoming for all of us 

 to look to the great work that has been accomplished by our 

 united efforts, rather than to the single share of each." 



The transmission of observations by telegraph between Cam- 

 bridge, New York, Philadelphia, and Washington furnished 

 Walker an opportunity for another important discovery. He 

 found that an appreciable time was required for the passage of 

 these signals, and that this time was less than one tenth of that 

 required for the passage of light over an equal distance in space. 

 This result was so greatly at variance with the ideas of electricity 

 current at the time that it was not accepted in America until the 

 celebrated velocity experiments between St. Louis and Washing- 

 ton put it beyond question, and even after that some European 

 physicists still refused to be convinced. While the matter was 

 in dispute Walker was generous with aid and encouragement to 

 those who sought to test his discovery, whether their results 

 seemed likely to conflict with or to confirm his own. 



The English Nautical Almanac for 1856 (issued in 1853) con- 

 tained a profound discussion, by the astronomer Adams, of the 

 amount of the lunar parallax. In this paper Adams showed that 

 the tables of Burckhardt, which had been the standard ones, con- 

 tained errors sometimes amounting to G", and pointed out the 

 effect that such errors must have upon determinations of longi- 

 tude from occultations. In the greater part of this discovery 

 Walker had anticipated the renowned Adams by more than four 

 years. In April, 1848, he had presented to his chief in the Coast 

 Survey a report on longitudes in the course of which he pointed 

 out the chief errors of Burckhardt's tables, giving four out of the 

 five principal terms with remarkable precision. 



Mr. Walker's intellectual labor was intense and unremitting ; 

 it was scarcely interrupted even in summer, when he was accus- 

 tomed to betake himself to Cambridge, to escape the heat of Wash- 

 ington. During one of these summer sojourns, in August, 1851, 

 he suffered a slight attack of paralysis, which for a few days de- 

 prived him of the use of one hand. This warning and the en- 

 treaties of his friends were not enough to induce him to relax his 

 exertions. In the following autumn he took charge of the expe- 

 dition for determining telegraphically the differences of longitude 

 between Halifax, Bangor, and Cambridge. Immediately after liis 

 return to Washington, at about the end of December, symptoms 



