6 THETRANSATLANTICLONGITUDE. 



Atlantic longitude Avas specially requirecP by law ; and the thorough accuracy of 

 Prof. Newcomb's investigations is well known to astronomers. Yet the result of the 

 latest chronometric expedition differs from that deduced by Newcomb, — from moon- 

 culminations observed at the Washington Observatory since its reorganization, com- 

 pared with those observed at Greenwich, — by more than three and a half seconds of 

 time. 



The value employed by the Coast Survey from 1852 to 1859 was 5'' 8'"1P.2; since 

 1859 it has been 5"^ S"" 1P.8. 



III. 



HISTORY OF THE EXPEDITION. 



The building erected in Calais, Maine, and occupied as a longitude-station in 

 1857, was still in existence, though much dilapidated, the stone piers being undis- 

 turbed. Mr. George Davidson, Assistant in the Coast Survey, was to take charge 

 of this station, with Mr. S. C. Chandler, Jr., as aid. Mr. Dean was assigned to 

 the station at Heart's Content, with the assistance of Mr. Edward Goodfellow; 

 while I was to occupy the Valencia station, Mr. A. T. Mosman accompanying. 

 Each station required a small transit-instrument, a chronograph, and an astrono- 

 mical clock. 



The most questionable feature of the arrangement was the use of the land line 

 of Avire, about 1100 miles long, between Heart's Content and Calais. Hitherto 

 all our telegraphic longitudes have been determined without any use of " repeaters," 

 or double relay-magnets, which have been most carefully avoided as inevitably 

 introducing an additional element of error, or at least of uncertainty, into the result. 

 The armature-times of different electro-magnets, acted on by galvanic currents of 

 different intensities, enter into the result, and only their mean amount is elimi- 

 nated, while one-half their difference remains inseparably merged with the resultant 

 longitude. Between Calais and Heart's Content there were known to be not only 

 several of these repeaters, but also one or two stations at least where the messages 

 were received and re-sent by hand, without the intervention even of an automatic 

 " repeater." Yet not only our financial resources, but also our available time and 

 our supply of instruments, precluded the occupation of more than three stations at 

 once, and it was reluctantly decided to make use of so many repeaters in this 

 interval as careful investigation should show to be absolutely necessary. 



Messrs. Davidson and Dean left Boston for Halifax in the steamer of Sept. 5, 

 to make an examination of the condition of the telegraph line, and a week later 

 Messrs. Goodfellow, Mosman, and myself sailed in the Cunard steamship Asia, 

 bound for Liverpool, via Halifax and Queenstown, taking the instruments for 

 Newfoundland and Ireland. But a short time before our departure the welcome 

 tidings had arrived of the recovery, in mid-ocean, of the lost cable of 1865, and of 

 the successful continuation of this second line to Newfoimdland. 



To the courtesy and interest of the officers of the Cunard Company we were 

 indebted, from the beginning to the end of our expedition, for many favors and 



» Coast Survey Report, 1858, p. 32. 



