POLTTECHNIC ASSOCIATION PROCEEDINGS, 605 ' 



arranging the lips in a circular form, as when we pronounce the 

 letter O, and then gently expelling the smoke from their mouths. 



The function of the smoke in these exhibitions is simply to ren- 

 der the vortex rings visible. They are just as readily produced 

 in transparent air, as has been experimentally proved in various 

 ways. 



Prof. Tait, of the University of Glasgow, has recently performed 

 with smoke rings some curious and highly interesting experiments, 

 some of which I will now endeavor to reproduce upon a smaller 

 scale. 



I have here a large pasteboard millinery box, in the cover of 

 which are two circular holes, about three inches in diameter, one at 

 each end of the box. For smoke, I will mix the vapors of hydro- 

 chloric acid and ammonia. I first heat these two small saucers, and 

 then pour into each a small quantity of the proper liquid. I next 

 place the two saucers inside the box, and it becomes filled with a 

 densely white vapor. Every time I expel a little of this vapor 

 from one of the holes, by flapping a book on the palm of my hand 

 against the other hole, you will obsei've that the smoke issues forth 

 in the form of a cylindrical ring, moving in a line perpendicular to 

 the plane of the ring, and revolving rapidl}^ on its circular axis. 

 The direction of this rotation corresponds on the inner side of the 

 cylinder with that of the general motion of the ring, the outer side 

 moving in the opposite direction. 



Gaslight is by no means so favorable as daylight for the exhibi- 

 tion of these rings, which disappear or become very indistinct a3 

 they pass away from the immediate illumination of the gaslight to 

 more distant parts of the room. You perceive, however, that they 

 retain their peculiar form and whirling motion while they are 

 visible. On impelling two of them against each other, they are 

 not broken, but rebound from each other as though made of India 

 rubber. This also accords with the mathematical results obtained 

 by Helmholtz. 



Sir William Thomson, the distinguished Professor of Natural 

 Philosophy in the University of Edinburgh, at once seized upon 

 these results as the basis of a new theory of the molecular consti- 

 tution of matter. The construction of this theory has not yet been 

 made public, I believe; but it is understood that its distinguished 

 originator is still at work upon the mathematical investigations 

 connected with it. 



The fundamental idea of the hypothesis seems to be, that *• a 



