THE TRANSATLANTIC LONGITUDE. 79 



1. By the great chronometric expedition of 1844, the transit instru- 



ment being placed in the station of the trigonometrical 



survey 0"^ 41" 23\23 



2. By the telegraphic communication of 1862, the time instrument 



being placed at Knightstown, 



Greenwich to KnightstoAvn . . 0'' 41"° 9'. 81 

 Keduction to Feagh Main . . +13.56 



3. By this telegraphic communication in 1866, the transit-instru- 

 ment being placed at Foilhommerum, 



Greenwich to Foilhommerum . . 0^ 41°' 33'.29 

 Reduction to Feagh Main . . — 10.10 



41 23.37 



41 23.19 



From which he adopts 



Feagh Main west of Greenwich . . , , 41 23.29 



The variation of these measures may be accounted for in great degree by the 

 local deviations of the direction of gravity in this hiUy region, and their consequent 

 effect upon the geodetic reductions. 



4. Final Inferences. 



The combination of the three longitudes thus determined, gives — 



Greenwich — Foilhommerum, O*" 41™ 33'.29 



roilhommerum — Heart's Content, 2 51 56.54 



Heart's Content — Calais, 55 37. 12 



Greenwich — Calais, 4 29 7.55 



The Valencia observations having been made by, or referred to, Mr. Mosman 

 throughout the whole period, his personal equation is eliminated; the equation 

 between Messrs. Goodfellow and Dean, always small, may be regarded as trust- 

 worthy, and by a happy coincidence the personal equations of Mr. Boutelle on the 

 west, and of Mr. Mosman on the east, seem to be almost identical, so that even a 

 total disregard of this quantity would have resulted very nearly in its perfect elimi- 

 nation, the oceanic arc being diminished and the land arc increased, each by about 

 0M4. 



The only probable influence of personal equation in the entire longitude-measure- 

 ment, comprising, as it does, three-sixteenths of the Avhole circumference, lies in 

 the difference between the observations of Messrs. Dunkin and Boutelle. 



The longitude of Calais, as heretofore telegraphically determined, is aa follows: — 



Calais — Bangor, 



0" 



6- 



' 0'.31 



Bangor — Cambridge, 







9 



22.99 



Cambridge — New York, 







11 



26.07 



New York — Washington, 







12 



15.47 



Calais — Washington, 







39 



4.84 



whence Ave have 



Greenwich — Washington, S"" 8"° 12'.39 



The Seaton Station being 12'.44, and the dome of the Capitol 10M7, east of the 



