696 Dr. C. V. Burton : Notes on 



phenomenon, reservation being made of small residual effects, 

 evidenced to us by gravitation. Except for such residual 

 effects, the tentative conclusion (1) is suggested as applying 

 throughout the aetherial plenum, including those regions in 

 which matter is present. 



6. It should be remarked that, whereas the modern view of 

 atomic matter reduces all motion to stationary motions of the 

 sether, the suggestion now put forward reduces the motion of 

 each aether-element to stationary motion on a scale still more 

 minute. Though the indication thus afforded as to the nature 

 of the electric and magnetic vectors is but slight, it may be 

 pointed out that if an electromagnetic scheme can be formu- 

 lated in conformity with (1), it will apparently be free from a 

 difficulty which has embarrassed more than one hypothesis. 

 For let Q be any quantity which varies from point to point 

 of ihe setherial plenum, and let "dQ/'dt represent the time-rate 

 of change of Q at a point fixed in space, dQ,/dt being the rate 

 of change corresponding to a point which moves with the 

 sether ; then, in virtue of the kinematical relation 



^7 = 5T7 + u ^~ + v •£" + w 5T> 

 at ob ox oy o<2 



(1) would give 



d _ "b 

 dt lot 



(2) 



7. The processes concerned in the transmission of radiation 

 can with some confidence be defined in terms of the electric 

 and magnetic vectors, but so long as the nature of these 

 vectors is undetermined, the actual character of the vibration 

 necessarily remains unknown. Of all forms of transverse 

 waves, the most readily conceived is that which consists in 

 laminar motion of the medium, so that each infinitesimal 

 element concerned in the propagation of a wave-train suffers 

 bodily displacements in a plane transverse to the direction of 

 propagation, and acquires thereby kinetic energy which is 

 purely translational. So far as I am aware, this simple 

 laminar form of motion, with bodily translation of aether- 

 elements, has been assumed in nearly every attempt yet made 

 to define dynamically the nature of light-waves. This is 

 equally true of those hypotheses which are explicitly electro- 

 magnetic and of those which are not ; the optical theories of 

 Fresnel and MacCullagh, the labile (contractile) aether, vortex- 

 sponge aether, and quasi-rigid (gyrostatic) aether of Lord 

 Kelvin are among the most notable examples. 



