66 Sir Oliver Lodge [Feb. 21, 



higher than ours are at present — is a question far transcending the 

 Hmits of physical speculation." 



And there for the present I leave that aspect of the subject. 



I shall now attempt to illustrate some relations between ether and 

 matter. 



The question is often asked, is ether material ? This is largely 

 a question of words and convenience. Undoubtedly, the ether 

 belongs to the material or physical universe, but it is not ordinary 

 matter. I should prefer to say it is not " matter " at all. It may be 

 the substance or substratum or material of which matter is composed, 

 but it would be confusing and inconvenient not to be able to dis- 

 criminate between matter on the one hand, and ether on the other. 

 If you tie a knot on a bit of string, the knot is composed of string, 

 but the string is not composed of knots. If you have a smoke or 

 vortex-ring in the air, the vortex-ring is made of air, but the atmo- 

 sphere is not a vortex-ring ; and it would be only confusing to say 

 that it was. 



The essential distinction between matter and ether is that matter 

 moves^ in the sense that it has the property of locomotion and can 

 effect impact and bombardment : while ether is strained, and has the 

 property of exerting stress and recoil. All potential energy exists 

 in the ether. It may vibrate, and it may rotate, but as regards 

 locomotion it is stationary — the most stationary body we know — 

 absolutely stationary, so to speak ; our standard of rest. 



All that we ourselves can effect, in the material universe, is to 

 alter the motion and configui-ation of masses of matter ; we can 

 move matter, by our muscles, and that is all we can do directly : 

 everything else is indirect. 



But now comes the question, how is it possible for matter to be 

 composed of etlier ? How is it possible for a solid to be made out of 

 fluid ? A solid possesses the properties of rigidity, impenetrability, 

 elasticity, and such like ; how can these be imitated by a perfect 

 fluid such as the ether must be ? The answer is, they can be imitated 

 by a fluid in motion ; a statement which we make with couiidence as 

 the result of a great part of Lord Kelvin's work. 



It may be illustrated by a few experiments. 



A wiieel of spokes, transparent or permeable when stationary, 

 becomes opaque when revolving, so that a ball thrown ngainst it 

 does not go through, but rebounds. The motion only affects per- 

 meability to matter ; transparency to light is unaffected. 



A silk cord hanging from a pulley becomes rio:id and viscous when 

 put into rapid motion ; and pulses or waves which may be generated on 

 the cord travel along it with a speed equal to its own velocity, whatever 

 that velocity may be, so that they appear to stand still. This is a 

 case of kinetic rigidity ; and the fact that the wave-transmission 

 velocity is equal to the rotatory speed of the material, is typical and 



