188 THE REASON WHY. 



' Children's children are the crown of old men ; and the glory of children are 

 their fathers." PKOVERBS xvn. 



Because the attraction of cohesion draws the particles of soap 

 together, directly the bubble is set free from the bowl. 



Fig. 29. BLOWING SOAP BUBBLES. 



828. Why do bullies, blown in the sunshine, change their 

 colours ? 



Because the films of the bubbles constantly change in thickness, 

 through the atoms from the upper part descending towards the 

 bottom, and therefore the varying thickness of film refracts, in 

 different degrees, the rays of light. 



829. Why do bubbles burst ? 



Because the atoms that compose their films fall towards the 

 earth by gravitation; the upper portion of the bubbles then 

 becomes very thin, and as the denser air of the atmosphere presses 

 towards the warm breath within the bubble, it bursts the Him. 

 See 236. 237, etc., 501, etc. 



830. Why do balloons ascend in air ? 



Because the air or gas which they contain is specifically lighter 

 than the atmosphere; the atmosphere, therefore, forces itself 

 underneath the balloon, by its own tendency towards the earth, 

 and the balloon is thereby raised upwards. A balloon is but a 

 larger kind of bubble, made of stronger materials. 



831. Why does an air-balloon become inflated when the 

 spirit set upon the sponge is lit ? 



