200 POPULAR LECTURES AND ADDRESSES. 



To understand these derived waves, first you 

 must regard them as due to motion of the ether 

 round each spherule ; the spherule being almost 

 absolutely fixed, because its density is enormously 

 greater than that of the ether surrounding it. 

 The motion that the ether had in virtue of the 

 exciting beam of light alone, before the spherules 

 came into existence, may be regarded as being 

 compounded with the motion of the ether relatively 

 to each spherule, to produce the whole resultant 

 motion experienced by the ether when the beam 

 of light passes along the tube, and azure light 

 is seen proceeding from it laterally. Now this 

 second component motion is clearly the same as 

 the whole motion of the ether would be, if the 

 exciting light were annulled and each spherule 

 kept vibrating in the opposite direction, to and 

 fro through the same range as that which the 

 ether in its place had, in virtue of the exciting 

 light, when the spherule was not there. 



Supposing now, for a moment, that without 

 any exciting beam at all, a large number of 

 minute spherules are all kept vibrating through 



