no telegraphic operation for longitude, and of no step in the improvement 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 temporarily 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 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 confirm 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 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 accustomed to betake himself to Cambridge, to escape the heat of Washington. During one of these summer sojourns, in August, 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 Cambridge. Immediately after his return to Washington, at about the end of December, symptoms
