It 



NATURE 



I'/uly I, 1880 



the deflection was the greatest on connecting the terminals 

 with the galvanometer. 



If the fact already pointed out be taken into account, 

 that with a constant battery-potential, the difference of 

 potential between the terminals of a vacuum-tube varies, 

 in the same gas, according to the degree of exhaustion, it 

 follows that as soon as a discharge takes place, the 

 potential of the terminals will be lowered. One would 

 therefore expect to find what the before-cited experiments 

 indicated, namely, that the static charge of the terminals 

 would be greater when no discharge takes place than after 

 it has occurred, notwithstanding that a larger number of 

 cells may have been employed in the latter case than in 

 the former, for the authors have shown {Phil. Trans., 

 vol. clxxi. p. 67) that a tube-potential may be only 430 

 cells, although the battery connected with its terminals is 

 1 1,000 cells. 



The authors believe, therefore, that the experiments 

 point conclusively to the deduction that the current ob- 

 tained from the terminals of a vacuum tube, after having 

 been disconnected from the battery, is solely due to a 

 static charge and not to a chcmital polarisation. 



An experiment was made with the apparatus arranged 

 as in Fig. 4, a tangent galvanometer being inserted in the 



circuit between the battery and the voltameter, the 77?,,, 

 shunt being used with the Thomson galvanometer. 



On keeping down the keys c and / after the voltameter 

 had been connected with three cells, the deflection, which 

 at first was 9S4 divisions, fell in — 



so that it was evident that a current was kept up by the 

 voltameter for a considerable time after the battery had 

 been disconnected. 



In order to render evident the direction of the current 

 of polarisation of the voltameter the apparatus was 

 arranged as in Fig. 5, that is, the Thomson galvanometer, 

 with r^^r, shunt, was inserted in the circuit between the 

 battery and the voltameter. An adjustable shunt was fixed 

 between a and /' to permit the greater part of the current 

 to pass through it. A phte of metal, ss, was provided to 

 slip under t' and /to short circuit the return current through 

 the galvanometer. The shunt which was found just 

 sufficient to carry the major part of the current, and yet 

 permit sufficient to traverse the voltameter to produce a 

 just visible evolution of gas, was 13 ohms. 



On connecting the battery, the current was in the 

 direction of the lower arrow, and the deviation 133 

 divisions say to the left ; on pressing down the keys on 

 to the metal slip placed under them to short circuit the 

 current, after the battery had been disconnected, the 

 return current was in the reverse direction, as shown by 

 the upper dotted arrow, the deviation being 425 divisions 

 to the right. Even without pressing down the keys on to 

 the metal slip nearly the same deviation was obtained on 

 disconnecting battery for the return current then traversed 

 the shunt from a to /'. 



L)n substituting either the bell-jar, with disk terminals, 

 or the tube 199 for the voltameter, the deflection of the 

 return static charge was in the same direction as the 

 return current from the voltameter, so that, as was before 

 stated, no inference can be drawn from the direction of 

 the current as to its being produced by polarisation or a 

 static charge. The authors conclude by saying : — We 

 think, however, that we have shown that the effect in the 

 case of a vacuum-tube is due to a static charge, and not 

 to a polarisation of the terminals. We rest our opinion 

 mainly on the fact that a greater deflection is produced, 

 when the potential has not been lessened by a discharge 

 through tlie tube, than that which occurs after the dis- 

 charge has taken place, which, it had been surmised, 

 might possibly produce a chemical polarisation. 



THE LATE M. GAUGAIN 



SCIENCE has to deplore the loss of an industrious but 

 unobtrusive worker in the person of Jean-Mothee 

 Gaugain, who died at the village of St. Martin d'Estreaux, 



