12 Prof. R. Ball on Vortex-rings in Air. 



experiments, showing a constant specific heat of air at different 

 densities which I have recently obtained from a repetition of some 

 of his experiments in a different shape ; and I hope to be able 

 soon to complete some experiments which should furnish addi- 

 tional proof of the actual disappearance of heat in the produc- 

 tion of work in the steam-engine. The want of such direct 

 proof is acknowledged ; and its importance is evident when we 

 consider how intimate is the connexion between a more exten- 

 sive knowledge of this subject in a practical point of view and 

 the improvements to be made in the wide field which still re- 

 mains open for effecting economy of fuel in the working of our 

 thermic prime movers. 

 Palermo, April 10, 1868. 



II. On Vortex-rings in Air. 

 By Professor Robert Ball. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



THE production of vortex-rings in air is experimentally shown 

 by the interesting phenomena produced by Professor Tait. 

 These are described by Sir William Thomson in the Philosophical 

 Magazine for July 1867. I repeated these experiments with the 

 kind aid of Dr. Emerson Reynolds ; in doing so an interesting 

 variation of them presented itself which renders the air-rings ac- 

 tually visible. 



While engaged on this subject, Mr. Yeates suggested to me to 

 try the effect of discharging an air-ring at a column of smoke ; 

 this was done, and a most curious and unexpected appearance 

 was the result. The box employed was a 2-feet cube, and had 

 a hole 8 inches in diameter, the side opposite having a piece of 

 stout sacking strained over it. A blow on the sacking causes an 

 air-ring to dart from the hole. Two large flasks containing re- 

 spectively hydrochloric acid and ammonia were arranged with 

 their mouths in close proximity and their contents vigorously 

 boiled ; from the union of their vapours a dense column of the 

 fumes of chloride of ammonium ascended. This apparatus was 

 placed about eight or ten feet in front of the box. An air-ring 

 on first leaving the box was of course invisible; when it reached 

 the column of smoke it could be seen to force its way through it ; 

 but when it left the column and during its subsequent existence 

 its appearance was very remarkable. At first the idea suggested 

 itself that the single air-ring had formed two concentric smoke- 

 rings ; but closer examination and an improved column of smoke 

 showed what had really occurred. The air-ring had penetrated 



