PHYSICAL PARADOXES. 



When the flask is closed, place it in any 

 convenient holder, as in Fig. 33, and wait a few 

 moments. The surrounding air, which, in com- 

 parison with boiling water, is cool, soon con- 

 denses some of the steam inside, and cools the 

 rest. This means that the 

 molecules are darting about 

 with less vigour, striking less 

 forcibly the inside of the glass, 

 and so exercising less pressure 

 upon it. But the pressure on 

 the outside remains the same 

 as ever nearly fifteen pounds 

 to the square inch, many hun- 

 dreds of pounds altogether over 

 the whole outer surface. This 

 is now unbalanced by the 

 FLASK UNDER ATMo- diminished steam pressure on 



SPHERIC PRESSURE. , . ... , , L , 



the inside, and the flask may 

 collapse, with the results already described. 



The reason of the loud noise is that the air 

 outside the flask, powerfully pressing inwards, 

 rushes, when the flask collapses, towards the 

 centre, where it meets together from all sides 

 with a violent shock. The reason why glass 

 flies for some distance is that some pieces, 

 driven in forcibly towards the centre, happen 

 to meet none coming in the opposite direction, 

 and so fly far past the centre outwards on the 

 opposite side. 



If the flask be of thin glass, and the bottom 

 144 



FIG. 33.-COLLAP8E OF 



