THE TRANSATLANTIC LONGITUDE. 13 



my request for a telegraphic connection between our station-point and Greenwich, 

 and assumed all the labor and embarrassment of the necessary arrangements, had 

 carried out the series of exchanges with FoUhommerum, an undertaking attended 

 with no little inconvenience and vexation from the various difficulties attending 

 land lines, especially when a submarine cable of the length of that across the Irish 

 Channel forms a part of the circuit. After many fruitless attempts, clock-signals 

 were exchanged on three nights, upon two of which the time was well determined 

 at both places. 



Upon the 20th November, the weather at Heart's Content, as well as at Valen- 

 cia, was extremely unpromising; no communication had yet been obtained between 

 that station and Calais, and it seemed best, on all accounts, to bring our cable 

 signals also to an end. After visiting Greenwich to oifer such aid in the reduction 

 of the longitude-exchanges with that Observatory as might be acceptable to the 

 Astronomer Royal, Mr. Mosman reached home on the 22d December, and I fol- 

 lowed four weeks later. 



The personal error, with other loss of time in observing signals^ has happily 

 proved more constant and more measurable than I had ventured to anticipate. No 

 matter how great the interval, the resultant longitude will only be aifected by one- 

 half the diiference of the values for the two observers ; while the average value for 

 the two observers could be merged with the time of transmission for the signals. 

 It is not the least satisfactory of our results that this interval proved capable of 

 measurement with a degree of accuracy which leaves no ground for apprehension 

 that it has appreciably affected our value for the longitude, and which enables us 

 to infer the velocity of transmission within restricted limits of probable error. 



The exchanges between Heart's Content and Calais were far less satisfactory. 

 Notwithstanding the laborious precautions taken by Mr. Davidson, all efforts at 

 direct communication proved unavailing, day after day, and week after week. 

 Mr. Davidson's health became seriously impaired, and Mr. F. W. Perkins Avas 

 added to the Calais party, joining it on the 12th November. Finally, Mr. Davidson 

 being called to important duties at the Isthmus of Darien, was compelled to leave 

 Calais, and Mr. Charles O. Boutelle, one of the most experienced officers of the 

 Survey, was assigned to the charge of the station. StiU, the necessity of an inter- 

 mediate astronomical station at Port Hood or Aspy Bay seemed inevitable, when 

 suddenly, on the 11th December, only a couple of hours before Mr. Boutelle's 

 arrival, the long-desired communication was found to be established. A sharp 

 frost had thrown the otherwise defective line into a condition of admirable insula- 

 tion, so that an interchange of clock-signals was effected without difficulty. Com- 

 parisons of clock-time at the two stations were also made on the 12th, 14th, and 

 16th December, though not in a manner wholly satisfactory, since clouds inter- 

 fered with the attainment of sufficient observations for time. At this juncture 

 Mr. Dean, at Heart's Content, decided to discontinue observations, and dismount 

 his instruments, so that the work was brought to a close, the Newfoundland 

 observers reaching Boston again in the last week of December. 



In reducing the observations, I have been aided to some extent by Mr. Mosman, 

 but chiefly by Mr. Chandler, who has for several years rendered efficient and skilful 



