52 SCIENCE AND IMMORTALITY 



crushing together the molecules of air into a liquid 

 — liquid air. By means of heating water we obtain 

 steam ; by cooling steam we obtain water. 



The difference between the molecular distances 

 in the case of a liquid and gas may be very great ; 

 thus water vapour occupies hundreds of times the 

 space occupied by the same weight of water. It is 

 the violent separation of the water molecules in 

 steam that makes steam such a tremendous energy. 

 The infinitesimal water molecules charging about, 

 hustling and colliding, trying to get away from 

 each other, lift a colossal piston ; then, catching a 

 chill, lose all energy, and fall in a heap like dew. 

 It is strange to think how molecules of water, 

 scourged apart by heat, carry men over continents 

 and seas ; and how molecules of petrol, driven 

 apart by a tiny spark, whizz the throbbing motor 

 car along the dusty road. It is strange also to think 

 how molecules of dynamite, separated or broken, 

 may leap apart with force sufficient to destroy a 

 city, and how a few grains of the molecules of the 

 active substance of tetanus might kill every man 

 in London. Roscoe states that if we could convert 

 the whole of the heat which can be obtained from 

 a pound of coal into mechanical energy it would 

 suffice to pitch the coal two thousand miles high. 

 Infinitesimally small as atoms and molecules are, 

 they yet are capable of tremendous violence and 



