92 



THE TRANSATLANTIC LONGITUDE. 



Series I. — 



Newfoundland Signals, Valencia Battery. 







Earth-con- 



Transmission-time. 



Excess for 



Exp't. 



Date. 



nection. 



Make-circuits. 



Break-circuit. 



make-circuits. 



L2 



Nov. 1 



Zinc 



0^05 



0»39 



-f0^26 



L3 



u « 



None 



0.80 



0.61 



-fO.19 



I. 1 



Nov. 10 



Middle 



0..54 



0.22 



+ 0.32 



I. 2 



" " 



Zinc 



o.'r2 



0.30 



+ 0.42 



L3 



" " 



None 



0.4t 



0.31 



+ 0.16 



Series III. — Valencia Signals, Newfoundland Battery. 



Ill 1 I Nov. 16 

 in. 2 " 

 IIL3 " " 



Middle 



Zinc 



None 



0^44 

 43 

 0.36 



0^64 

 0.56 

 0.34 



—0^20 

 —0.13 



+ 0.02 



These values are rudely confirmatory of those deduced by the first method. They 

 show at any rate a difi"erence in velocity for the two kinds of signals, which becomes 

 very large when the tension at any part of the circuit is disturbed by an earth-con- 

 nection. And they also indicate that a full charge or discharge of the cable is not 

 requisite for a, make-circuit or break-circuit signal. 



In the experience of the Coast Survey since 1851, the break-circuit signals, which 

 have exclusively been employed for longitude-determinations, have varied compara- 

 tively little in their velocity. This question has been investigated in every instance ; 

 and, in many cases, large changes have been made in the battery-power and in the 

 connections, for the purpose of observing the efi'ect upon the transmission-time. I 

 have no access to the records of these experiments at present ; but the results have 

 in general shown, that with a well insulated line of uncoated iron wire, of the size 

 ordinarily employed^ (the earth itself forming half the circuit), the time required 

 for the signals to reach their destination is not far from 0'.07 for each thousand 

 miles, or, roughly, that their velocity is 22,000 kilometers to the second. The ne- 

 cessary interpolation of repeaters between Heart's Content and Calais precludes any 

 determination of the velocity of the electrical action ; but the average interval of 

 time consumed in the passage of a signal between these two stations was 0'.277, the 

 distance being 1090 miles, and four repeaters being interposed. 



During the intervals between the signals, the electrical condition of the cable 

 was undisturbed, and no extraneous infiuence prevented its return to a state of 

 equilibrium. The signals were a quarter of a second long, as nearly as might be, 

 and intervals of five or of ten seconds elapsed between the successive signals, each 

 pair of " sets" having fourteen intervals of 5^ each, and five intervals of 10". Upon 

 no one of the five longitude-nights was there any direct connection between the 

 cable and the earth. The two extremities of the cable were connected with con- 

 densers on the 25th and 28th October, and all signals on those occasions were 

 therefore given by induction only ; while on the 5th, 6th, and 9th November, a 

 complete circuit was formed by the two cables, and the battery at the receiving- 

 station was short-circuited. On these last two nights the two cables were not con- 



' That called in commerce No. 9, weighing about 320 pounds to the mile, or 78.4 grams to the 

 meter. 



