1882.] on Matter and 3Iagneto-Electric Action. 85 



It is true that sucli a view of the case would seem to imply that, in 

 gaseous media, the better the vacuum the more easily can the elec- 

 tricity pass ; and that this might at first sight appear to be at variance 

 with the known fact that the resistance of a tube decreases with the 

 pressure until a minimum, determinate for each kind of gas, and then 

 increases. But it has been suggested by Edlund (' Annales de Chemie 

 et de Physique,' 1881, tom. iii. p. 199) that the resistance of a tube 

 may really consist of two parts, first that due to the passage of the 

 electricity through the gas itself and, secondly, that due to its passage 

 from the terminals to the gas ; and also that the former decreases, 

 while the latter increases, as the pressure is lowered. On this 

 supposition the observed phenomena may be explained, without 

 assigning any limit to the facility with which electricity may traverse 

 the most vacuous space. 



We may even carry the suggestion of a resistance of the second 

 kind a little further, and suppose that there is a resistance due to the 

 passage of electricity from a medium of one density to that of another, 

 or from layer to layer of different degrees of pressure. And from 

 this point of view we may regard the striae as expressions of resistance 

 due to the varying pressure in different parts of the tube. Into the 

 question, whence this variation of pressure, I am not at present 

 prepared to enter ; it must suffice for this evening to have shown that 

 the conclusions which we have drawn from our experiments are not 

 in disaccordance with other known phenomena of the electrical 

 discharge. 



[W. S.] 



