570 



Drs. De La Rue and H. W. Miiller. [June 17> 



So that in every case when the discharge did not take place, the 

 deflection, on connecting the terminals with the galvanometer, was the 

 greatest. 



If the fact which we have already pointed out be taken into ac- 

 count, that with a constant battery-potential, the difference of poten- 

 tial 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. 

 We should therefore expect to find what the before- cited experi- 

 ments 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 em- 

 ployed in the latter case than in the former, for we 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 11,000 

 cells. 



We believe, therefore, that the experiments point conclusively to 

 the deduction that the current obtained 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 chemical polarisation. 



Fig. 6. 



TANGENT 



An experiment was made with the apparatus arranged as in fig. 6, 



