PHYSICAL PARADOXES. 



The fact is, quite literally, that the dish is 

 too hot to boil the water. It is so hot that 

 before the water can quite touch it, its heat 

 vaporises some of the water off the nearest sur- 

 face and keeps it in the condition of vapour 

 next the water and of gas next the dish. Thus 

 there is a thin layer of gas and vapour between 

 the water and the dish. The two never come 

 into actual contact, because of the intermediate 

 cushion on which the water rests. 



Now, gases and vapours are very poor 

 conductors of heat. Consequently the heat 

 of the dish, great though it be, cannot get 

 through this non-conducting cushion quite fast 

 enough to boil the water, and only slowly 

 vaporises it. 



The water, being unable to get within mole- 

 cular distance of the copper, cannot suffer 

 capillary attraction from it, as from things 

 which it wets ; and so its shape is left to be 

 determined by its surface tension and weight, 

 as with quicksilver on things which it does not 

 wet. 



Hence very small drops assume an approxi- 

 mately spherical shape, while larger masses are 

 flattened by their own weight into the spheroidal 

 form which, as we have seen, gives its name 

 to this condition of matter. 



A very simple and very efficient apparatus 

 for demonstrating the spheroidal state is a 

 penny beaten smooth and slightly concave by 



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