SEARS COOK WALKER. 433 



accomplished by our united efforts, rather than to the single 

 share of each." 



The transmission of observations by telegraph between 

 Cambridge, 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 Washington 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 con- 

 firm his own. 



The English Nautical Almanac for 1856 (issued in 1853) 

 contained 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, contained errors sometimes amounting to 6", and pointed 

 out the effect that such errors- must have upon determinations 

 of longitude from occultations. In the greater part of this dis- 

 covery 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 labour was intense and unremit- 

 ting ; it was scarcely interrupted even in summer, when he was 

 accustomed to betake himself to Cambridge, to escape the heat 

 of Washington. During one of these summer sojourns, in Au- 

 gust, 1851, he suffered a slight attack of paralysis, which for a 

 few days deprived him of the use of one hand. This warning 

 and the entreaties of his friends were not enough to induce 

 him to relax his exertions. In the following autumn he took 

 charge of the expedition for determining telegraphically the 

 differences of longitude between Halifax, Bangor, and Cam- 

 bridge. Immediately after his return to Washington, at about 



