230 Mr. E. H. Cook on the Existence of 



Another experiment which seems difficult of explanation is 

 that it is impossible to cause the electric discharge to occur in 

 a perfect vacuum. Ether is present in this case also ; yet this 

 ether is unable to transmit the electricity. Whatever this 

 electricity may be, it is certainly something which is much 

 like light and heat, it is therefore probably molecular motion 

 of some kind. If molecular motion, our ether ought to be 

 able to transmit it ; as it does not do so we are left to choose 

 between two alternatives — either to say electricity is not due 

 to molecular motion, or that no substance of the nature of 

 ether is present. Evidence seems to be accumulating to show 

 that electricity is due to molecular motion ; and we must there- 

 fore conclude that no ether is present. 



Thirdly, let us consider Faraday's experiment with the "heavy 

 glass/' When a polarized ray is passed along the axis of a prism 

 of a transparent substance which under ordinary conditions is 

 optically inactive, and the prism placed in the magnetic field, 

 then the substance becomes able to turn the plane of polarization. 

 Thus, if a polarized ray is sent through a prism of this glass which 

 is placed between the poles of an electromagnet, the plane of 

 polarization is immediately turned. The reason assigned for 

 this peculiar action by Faraday is that the magnet has caused 

 a temporary difference in the molecular constitution of the 

 substance ; and he finds that any cause which impedes the 

 development of this power of rotation also impedes molecular 

 displacement. But Faraday does not commit himself to the 

 statement that this alteration of molecular grouping causes an 

 alteration in the constitution of the ether of such a character 

 as to cause it to vibrate in a particular plane. He simply 

 states that a molecular rearrangement has produced the effect, 

 and evidently considers this a sufficient explanation. 



Two observations recently made are also difficult of expla- 

 nation on the ethereal theory, viz. the increase of the electrical 

 resistance of selenium by its exposure to light, and Dr. Kerr's 

 experiments with the light reflected from the polished pole of 

 a magnet (see Phil. Mag. May 1877 and March 1878). In 

 the first of these we find that the vibratory movement of light 

 affects the material particles of matter ; for we believe that the 

 particles of the body are alone concerned in the transmission of 

 electricity. This difficulty may be overcome by assuming 

 the ether to be the medium for the conduction of electri- 

 city as it is of light ; but up to the present, I believe, this 

 theory has not been propounded. Dr.. Kerr finds that the 

 light reflected from the polished pole of a magnet is polarized. 

 We must therefore suppose that the ether is susceptible of mag- 

 netic influence. May I ask if it contains the two magnetic 



