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NATURE 



[June 21, 1888 



by a strange development of modern enterprise. On 

 the other hand, the bubble has occupied the minds 

 of scientific men of all times. Sir Isaac Newton, Sir 

 David Brewster, and Faraday, not to mention many 

 others, devoted themselves to the soap-bubble as a means 

 for investigating the subtleties of light. Plateau a few 

 years ago delighted men of science with that wonderful 

 book in which he, a blind man, expounded, in the clearest 

 and most elegant manner, the result of years of labour on 

 this one subject. Lately, Profs. Reinold and Riicker 

 have employed the soap-film in investigations which 

 tend to throw more light on the molecular constitution of 

 bodies. These experiments will be remembered by all 

 who saw them as being no less beautiful than instructive. 

 The latest experiments with bubbles, which were shown 

 by Mr. C. V. Boys to the Physical Society and at the 

 Royal Society conversazione, and of which a full account 

 is to be found in the May number of the Philosophical 

 Magazine, depend upon no property which is not well 

 known, and, unlik e those referred to above, are not intended 

 to increase our scientific knowledge ; and yet no one would 

 have ventured to predict that bubbles would submit to the 

 treatment described in the paper, or would have expected 

 such simple means to produce such beautiful results. 



The first property of the soap-film turned to account 

 is that strange reluctance of two bubbles to touch one 

 another. Just as a bubble may be danced on the sleeve 

 of a serge coat, or even embraced, without wetting the 

 sleeve or being broken, so can two bubbles be pressed 

 together until they are materially deformed without 

 really touching one another at all. Cne bubble may be 

 blown inside another, and if the heavy drops which 

 accumulate at the bottom are removed, the inner one may 

 be detached and rolled about within the outer one ; or the 

 outer one, held by two moistened rings of wire (Fig. 1), 



Fig. i. Fig. 2. 



may be pulled out so as to squeeze the inner one into an 

 oval form (Fig. 2), or may even be swung round and 

 round, and yet the inner one remains free and independent, 

 and when the outer is broken it floats gently away. If 

 the inner one is coloured with the fluorescent material 

 uranine, it shines with a green light, while the outer one 

 remains clear as at first, showing that there is no mixture 

 and no contact. 



When the inner bubble is blown with coal gas, it rests, 

 against the upper side of the outer one (Fig. 3), pulling it 



Fig. 3. 



Fig. 



Fig. 5. 



more and more out of shape as its size increases (Fig. 4). 

 It can even be made to tear the outer one off the ring to 

 which it was attached, after which the two bubbles rise in 

 the air one inside the other. The outer bubble may be 

 held by a light ring of thin wire to which thread and paper 

 are attached, and then when an inner bubble of coal gas is 

 blown, it will carry up the outer bubble, ring,paper, and all ; 

 and yet, in spite of this weight pressing them together, the 



inner bubble refuses to touch the outer one. If a little gas 

 is let into the outer of two bubbles, the inner one will 

 remain suspended like Mahomet's coffin (Fig. 5). 



Diffusion of gas through a soap-film is shown by 

 lowering a bell-jar of coal-gas over a bubble in which a 

 second one is floating (Fig. 6). By degrees the gas pene- 

 trates the outer bubble, until the inner one, insufficiently 

 buoyed up, gently sinks down. 



The heavy and inflammable vapour of ether is made 

 use of to show the rapidity with which the vapour 

 of a liquid which will mix with the soap solution 

 will penetrate through the walls of a bubble. A large 



Fig. 6. 



Fig. 



inverted bell-jar has some ether poured into it, after which) 

 bubbles blown with air in the usual way may be dropped! 

 into the jar, when they will float upon the vapour. They arc; 

 then taken out and carried to a flame, when a blaze oi 

 light shows that the inflammable vapour has penetrated) 

 through the film. A bubble blown at the end of a widei 

 tube and lowered into the vapour hangs like a heavy 

 drop when removed ; and if held in the beam of an electrici 

 light the vapour is seen oozing through the film andfallingl 

 away in a heavy stream, while a light applied to the! 



Fig. 8. 



mouth of the tube fires the issuing inflammable vapour. 

 and a large flame like that of a bunsen burner is the 

 result (Fig. 7). 



A variety of experiments are described in which bubbles 

 are rolled along troughs made of soap-film — either straight 

 circular,or spiral — the prominent feature being that bubbles 

 will roll upon or within one another as if they were made 

 of india-rubber ; they will even,where apparently in contact 

 take up the vibrations of a tuning-fork, and this will no; 

 force them to touch. There is one influence, however 

 which they cannot resist, and that is electrification. Wher 1 

 two bubbles which are resting against one another (Fig. 8) 

 provided that one is not within the other, are exposed tc 

 the influence of an even feebly electrified body, they in- ; 



