THE TRANSATLANTIC LONGITUDE. 77 



transit-observations themselves." At any rate the result obtained from the exchanges 

 of Dec. 12 seemed entitled to small reliance, before its large discordance from the 

 other values was manifest. 



Reducing all the values to Mr. BouteUe, and rejecting that of December 12 from 

 the mean, we thus obtain : — 



December 11, 0" SS-" 3T^93 

 12, [3T.53] 



14, 37.84 



16, 37.82 



Mean, 55 37.86 

 which diminished by 0'.14 to correct for the personal equation between Messrs. 

 BouteUe and Goodfellow, becomes — 



7, =0^55- 37^72. 



3. Greeinvich and Foilliommerum. 



It has been already stated that the Astronomer Royal cordially acceded to my 

 request that he would take measures for the determination of the longitude between 

 Greenwich and our station at Foilhommerum. This request was made with diffi- 

 dence, since Mr. Airy had already determined the longitude of two other points in 

 Valencia with all possible care, — Feagh Main, the highest point on the island, having 

 been measured chronometrically in 1844, and Knightsto^vn telegraphically in 1862, — 

 so that the establishment of our station at Foilhommerum implied the determination 

 of an additional arc in order to connect it with Greenwich, Avhereas we had hoped 

 to adopt the old station of the Astronomer Royal at Knightstown, six miles to the 

 eastward. 



The arrangements for the telegraphic interchange of sig-nals with Greenwich 

 were made by Mr. Airy, and the reductions were executed under his direction at 

 the Royal Observatory ; our own share in the work being limited to the operations 

 at Foilhommerum. Exchanges were attempted on ten nights between the 3d and 

 15th November, but were successful only on the 5th, 13th, and 14th. On the last 

 occasion the weather precluded us from obtaining any observations for time, so that 

 the result depends upon two nights' exchanges. These proved, however, very 

 accordant. 



The clock at each terminus was made to record itself upon the chronograph at 

 the other for half an hour, and the construction of the chronographic and signal- 

 giving apparatus at Greenwich required our clock-signals to be given by closing an 

 open circuit, not by interrupting a closed one, and the Greenwich signals to be 

 received in a similar way. To meet this need, the relay-magnet was modified, 

 while receiving signals, by transferring the conducting-stop of the armature to the 

 rear, so that the currents arriving at each second should interrupt the local circuit 

 of the chronograph-magnet like our own clock-signals. And in sending our 

 signals to Greenwich the connections of the main and local circuits with the relay- 

 magnet thus modified were respectively reversed, so that an interruption of the local 

 circuit by our own clock produced a closure of the main circuit, which transmitted 

 a current to Greenwich. Thus no loss of time was entailed in receiving signals; 



