ELECTRIC LIGHTS. 177 



17. A denser part of a ring may sometimes be seen 

 to be travelling round the ring without apparent rotation 

 of the ring itself, but this phenomenon I have not been 

 able to reproduce at will. 



18. Sometimes a spiral movement may be seen to be 

 taking place in and out'as well as round the ring. 



19. If one is provided with two boxes for forming 

 these rings, they may be used in conjunction. Rings 

 may be made to move towards and away from each 

 other at any angle and at different velocities. Rings of 

 different sizes moving towards each other in the same 

 line present a singular phenomenon. The smaller 

 one will go through the larger, and the one with the less 

 velocity will be brought to a standstill in the air, 

 while the other one goes on with lessened velocity. 

 After the moving one has advanced a foot or two, the 

 arrested one will again start up as if it had been pushed 

 in the direction it originally had. Showing in a curious 

 way that the forward movement of the vortex ring is 

 necessitated by the motion that constitutes the ring 

 itself. 



The liquids in the saucers may get too dilute to 

 serve for experiment for all the above indicated ones. 

 The ammonia water may get a crust of chloride formed 

 on its surface which will need removal. If the liquids 

 be freshly heated they will again serve for experiments 

 for a few minutes. In order that a roomful may see 

 the rings to good advantage, it will be better to have a 

 dark background, and have the rings lighted by a beam 

 of light parallel to the general direction of their motions. 

 If the fumes are not quite dense, they may not be easily 

 seen at the distance of fifteen or more feet. With such a 

 series of experiments various properties of matter may 

 be illustrated. For example, the external and internal 



