410 Mr. C. V. Boys's Experiments 



Everyone is familiar with the fact that a soap-bubble may 

 be supported or even struck by a piece of baize or wool 

 without coming into real contact with the material ; it is also 

 well known that two bubbles supported on the pipes from 

 which they are blown, or on rings, may be pressed or knocked 

 together with such violence as to materially alter their shape, 

 and yet they do not come into real contact; there is a film of 

 air between them which they are unable to squeeze out. This 

 film, though thin to ordinary tests, is so thick that the colours 

 of Newton's rings are only seen when one of the bubbles is 

 very small, so that the air is squeezed out the more readily. 

 If the pressure is increased so as to make a real contact, the 

 bubbles both instantly burst. That this pressure may be 

 made great before the true contact takes place will be shown 

 in a variety of ways hereafter ; but the following simple 

 experiment makes it very evident that the air-film will 

 prevent the contact of two soap-films that are pressed together. 



Exp. 1. — Blow a bubble about 9 cm. in diameter, and place 

 it on a ring with a diameter of about 7 cm. This bubble may 

 be pulled or pushed through the ring by means of a smaller 

 wire ring which serves as a handle. (See 'Nature,' 1871, 

 p. 395.) It may be so adjusted that the weight of the ring- 

 will not pull it through. Then a ring larger than the bubble, 

 carrying a plane film, can be used to push it up and down 

 through the ring, and yet the two films do not touch (fig. 1, 



Bearing this fact in mind, that two bubbles may press one 

 another without true contact, I hoped to be able to blow and 

 detach one bubble within another, and let it roll about within 

 the larger bubble. This, however, is made difficult by the 

 accumulation of a small quantity of solution at the bottom of 

 each, the weight of which is able immediately to press through 

 the air-film between them and so cause both bubbles to burst. 

 However, the experiment can be performed in the following 

 manner: — 



Exp. 2. — Blow a bubble on the lower side of the same 

 ring that was used in Exp. 1, and if a large drop does 

 not remain hanging to the bubble slowly apply solution to 

 any part until as great a drop as can safely be carried has 

 accumulated. Then pass the end of the pipe through the 

 upper side of the bubble, and blow another inside, but take 

 care in this case to have no excess of liquid. When the 

 inner bubble is about twice as large as the outer one was at 

 first, remove the pipe with a rapid movement. The inner one 

 will now fall gently and rest within the outer one, the heavy 

 drop pulling the thick part of the outer bubble out of reach 



