388 iScientiJlo Intelligence. 



Thus Roller found that the specific resistauces of petroleum, 

 turpentine, and distilled water, when determined from experi- 

 ments made with very thin layers of these substances, was very 

 much larger than when determined from experiments with thicker 

 layers. Even in the case of metals there is evidence that the 

 metal has to be of appreciable size if it is to conduct electricity. 

 The theory of the scattering of light by small particles shows 

 that, if we assume the truth of the electromagnetic theory of 

 light, the efiects should be different according as the small parti- 

 cles are insulators or conductors. When the small particles are 

 non-conductors, theory and experiment concur in showing that 

 the direction of complete polarization for the scattered light is at 

 right angles to the direction of the incident light ; while if the 

 small particles are conductors, theory indicates that the direction 

 of complete polarization makes an angle of 60° with the incident 

 light. This result is not, however, confirmed by the experiments 

 made by Prof. Threlfall on the scattering of light by very small 

 particles of gold. He found that the gold scattered the light in 

 just the same way as a non-conductor, giving complete polariza- 

 tion at right angles to the incident light. This would seem to 

 indicate that those very finely divided metallic particles no longer 

 acted as conductors. Thus there seems evidence that in the case 

 of conduction through gases, through badly conducting liquids 

 and through metals, electric conduction is a process which requires 

 a very considerable space and aggregations of large numbers of 

 molecules. I have not been able to find any direct experi- 

 mental evidence as to whether the same is true for electrolytes. 

 Experiments on the resistance of thin layers of electrolytes 

 would be of considerable interest, as according to one widely- 

 accepted view of electrolysis conduction through electrolytes, 

 so far from being effected by aggregations of molecules, takes 

 place by means of the ion, a structure simpler than that of the 

 molecule, so that if this represents the process of electrolytic 

 conduction, there would not seem room for the occurrence of an 

 effect which occurs with every other kind of conduction. 



In this building it is only fitting that some reference should 

 be made to the question of the movement of the ether. You 

 are all doubtless acquainted with the heroic attempts made by 

 Prof. Lodge to set the ether in motion, and how successfully the 

 ether resisted them. It seems to be conclusively proved that 

 a solid body in motion does not set in motion the ether at an 

 appreciable distance outside it ; so that if the ether is disturbed 

 at all in such a case, the disturbance is not comparable with that 

 produced by a solid moving through an incompressible fluid, but 

 must be more analogous to that which would be produced by the 

 motion through the liquid of a body of very open structure, such 

 as a piece of wire netting, where the motion of the fluid only 

 extends to a distance comparable with the diameter of the wire, 

 and not with that of the piece of netting. There is another class 

 of phenomena relating to the movement of the ether which is, I 



