60 Professor Thomson, Longitudinal Electric Waves, [Jan. 27, 



We thus see that on the electromagnetic theory normal waves 

 of very short wave lengths can be propagated if the ether is 

 moving. 



A normal wave in passing from one medium to another would 

 be deflected if the lines of electric intensity were bent in passing 

 from one medium to another. At the junction of two media of 

 different specific inductive capacity the lines of electric intensity 

 are refracted, being bent away from the normal as they pass from 

 a medium of small specific inductive capacity to one of large. 

 In the case of these very short waves there seems, however, no 

 reason to suppose that the specific inductive capacity of a medium 

 would differ from unity. For if we regard a molecule as made 

 up of a positively electrified atom joined to a negatively elec- 

 trified one, then, just as the magnetic permeability may be re- 

 garded as due to the setting of molecular magnets under the 

 influence of the magnetic force the specific inductive capacity 

 will be due to the setting of these molecules under the influence 

 of the electric intensity. If now the wave length of the electric 

 intensity is comparable with the size of a molecule, a molecule 

 at one part of its length will be acted on by a force tending to 

 make it set in one way, and at another part of its length by a force 

 tending to make it set in the opposite way ; the resultant effect 

 therefore will be little or nothing, and the specific inductive capacity 

 will practically be the same as that of a vacuum. 



Quite recently Professor Rontgen has discovered some remark- 

 able effects which he is inclined to attribute to normal waves. 

 We do not know enough about the laws governing those new 

 rays to be able to say whether they could or could not belong to 

 the type of normal waves we are investigating ; we do not even 

 know at present that they are normal waves at all. 



A series of photographs taken by Professor Rontgen' s method 

 was shown, and a photograph was taken during the meeting of the 

 Society. 



A very noticeable feature in the bulb producing these Rontgen 

 rays is the phosphorescence of the glass of the bulb. I thought it 

 therefore of interest to try if these rays were generated when the 

 phosphorescence of the glass was produced by other means than 

 the discharge from a negative electrode. To do this, I produced a 

 ring discharge in an electrodeless bulb; this when the pressure 

 of the gas is very low is accompanied by intense phosphorescence 

 of the glass. I exposed a photographic plate protected by thick 

 cardboard for an hour to such a bulb, but without the slightest 

 effect. I next tried filling the bulb with oxygen, a gas which 

 is itself made phosphorescent so as to have both the glass and the 

 gas phosphorescent, but again a photographic plate was not affected 

 after an hour's exposure. 



