346 ABSTRACTS OF SCIENTIFIC PAPERS 



were separated, a transient current was produced in the same direc- 

 tion as the current produced when the hot and cold ends were 

 suddenly joined. This led him to conclude that the currents in 

 question were due to the nearness of the ends, and that by main- 

 taining a state of loose contact a permanent current might be esta- 

 blished a conclusion which was verified by the experiments. Trial 

 was made of the comparative amounts of the effect in iron, copper, 

 and platinum. Experiments with joints between two metals showed 

 that the thermoelectric difference at a joint was often greatly in- 

 creased by substituting loose contact for tight contact, and even the 

 direction of the current was sometimes reversed. 



IV. On the True and False Discharge of a Coiled Electric Cable. 

 By Professor W. Thomson and Mr. Fleeming Jenkin ; ' Philo- 

 sophical Magazine,' September 1861. 



Mr. Jenkin had communicated to Professor Thomson, in 1859, 

 experimental results which showed that when a battery had been 

 applied to the near end of a coiled cable whose distant end was con- 

 nected to earth, if the near end were suddenly disconnected from the 

 battery and put to earth through a galvanometer, the deflection of 

 the galvanometer showed a ' false discharge,' that is, a current still 

 entering the cable from earth, in the same direction as the current 

 formerly supplied by the battery. In communicating this fact to 

 the British Association in 1859, Professor Thomson had explained 

 it as a result of the electromagnetic induction between different 

 portions of the coil, and had anticipated that no such false discharge 

 would be observed in a straight cable. The paper describes and 

 discusses Jenkin's experiments which, on being repeated, showed 

 that when the near end was put to earth the very first deflection of 

 the galvanometer there showed a back -flow or true discharge from 

 the cable, but this was quickly followed by a much larger opposite 

 deflection, forming the false discharge. The theoretical conclusion 

 that the false discharge would not be observed in submerged cables 

 was verified by Mr. Jenkin in experiments on the Bona Cable ; and 

 still more conclusively by Mr. Webb, whose letter on the subject (to 

 the Engineer of August 26, 1859) is appended to the paper. 



[This paper is reprinted as Article LXXXIII. in vol. ii. of Sir 

 W. Thomson's Mathematical and Physical Papers.] 



V. On the Retardation of Signals through long Submarine Cables. 

 1 British Association Report,' 1859, p. 251. 



[Abstract of a part of Art. VI. below.] 



