278 
POPULAR SCIENCE REVIEW. 
of matter in its wanderings amongst other exactly similar por- 
tions, ways have been found to do it. It may be argued that 
the influences which determine the path of a particular portion 
of water are slight, subtle, and uncertain, but not so much so as 
those which determine the path of a sheep. And yet thousands 
of sheep belonging to different owners have been from time im- 
memorial turned loose on the mountains, and although it pro- 
bably never occurred to anyone to reason out the paths of his 
particular sheep, they have been easily identified by the aid of 
a little colour. And that the same plan might be pursued with 
fluids, every column of smoke has been evidence. 
But these hints appear to have been entirely neglected, and 
it was left for Nature herself, when, as it were, fully satisfied 
with having maintained her secret so long, and tired of throwing- 
out hints which were not taken, at last to divulge the secret 
completely in the beautiful phenomenon of the smoke ring. At 
last ; for the smoke ring is probably a phenomenon of modern 
times. The curls of smoke, as they ascend in an open space, 
present to the eye . a hopeless entanglement ; and although, 
when we know what to look for, we can see as it were imperfect 
rings in almost every smoke cloud, it is rarely that anything 
sufficiently definite is formed to attract attention, or suggest 
anything more important than an accidental curl. The acciden- 
tal rings, when they are formed in a systematic manner, come 
either from the mouth of a gun, the puff of a steam-engine, or 
the mouth of a smoker, none of which circumstances existed in 
ancient times. 
Although, however, mathematicians can in no sense be said 
to have discovered the smoke ring, or the form of motion which 
it reveals, they were undoubtedly the first to invest it with im- 
portance. Had not Professor Helmholtz some twenty years ago 
called attention to the smoke ring by the beautiful mathemati- 
■cal explanation which he gave of its motion, it would in all 
probability still be regarded as a casual phenomenon, chiefly 
interesting from its beauty and rarity. Following close on 
Helmholtz came Sir William Thomson, who invested these rings 
with a transcendental interest by his suggestion that they are the 
type after which the molecules of solid matter are constituted. 
The next thing to enhance the interest which these rings 
•excited, was Professor Tait’s simple and perfect method * of pro- 
* The apparatus consists of a cubical box like a tea-chest, with a circular 
hole, six or eight inches in diameter, in its bottom, and a cloth loosely nailed 
•over the top in place of a lid. The box is set on its end. The fumes of 
hydrochloric acid and ammonia are separately introduced into the box, when 
-they combine and form a dense smoke, which is ejected from the orifice by 
patting the cloth. It appears that a somewhat similar form of apparatus 
was used by Faraday, and has long been known as a toy. — 0. R. 
