THE ETHER AND PONDERABLE MATTER 



vortex rings in air. The apparatus, which any one may 

 duplicate, consisted simply of a box with a hole bored 

 in one side, and a piece of canvas stretched across the 

 opposite side in lieu of boards. Fumes of chloride of 

 ammonia are generated within the box, merely to render 

 the air visible. By tapping with the hand on the canvas 

 side of the box, vortex rings of the clouded air are driven 

 out, precisely similar in appearance to those smoke-rings 

 which some expert tobacco-smokers can produce by tap- 

 ping on their cheeks, or to those larger ones which we 

 sometimes see blown out from the funnel of a locomo- 

 tive. 



The advantage of Professor Tait's apparatus is its 

 manageableness, and the certainty with which the de- 

 sired result can be produced. Before Lord Kelvin's in- 

 terested observation it threw out rings of various sizes, 

 which moved straight across the room at varying rates 

 of speed, according to the initial impulse, and which be- 

 haved very strangely when coming in contact with one 

 another. If, for example, a rapidly moving ring over- 

 took another moving in the same path, the one in ad- 

 vance seemed to pause, and to spread out its periphery 

 like an elastic band, while the pursuer seemed to con- 

 tract, till it actually slid through the orifice of the other, 

 after which each ring resumed its original size, and con- 

 tinued its course as if nothing had happened. When, on 

 the other hand, two rings moving in slightly different di- 

 rections came near each other, they seemed to have an 

 attraction for each other ; yet if they impinged, they 

 bounded away, quivering like elastic solids. If an effort 

 were made to grasp or to cut one of these rings, the subtle 

 thing shrunk from the contact, and slipped away as if it 

 were alive. 



239 



