342 FRAGMENTS OP SCIENCE. 



vapour was formed and lifted without being paid for in 

 the currency of solar heat ; no particle returns as water 

 to the sea without the exact quantitative restitution of 

 that heat. There is nothing gratuitous in physical 

 nature, no expenditure without equivalent gain, no gain 

 without equivalent expenditure. With inexorable con- 

 stancy the one accompanies the other, leaving no nook 

 or crevice between them for spontaneity to mingle with 

 the pure and necessary play of natural force. Has this 

 uniformity of nature ever been broken ? The reply is : 

 'Not to the knowledge of science.' 



What has been here stated regarding heat and 

 gravity applies to the whole of inorganic nature. Let 

 us take an illustration from chemistry. The metal 

 zinc may be burnt in oxygen, a perfectly definite 

 amount of heat being produced by the combustion of 

 a given weight of the metal. But zinc may also be 

 burnt in a liquid which contains a supply of oxygen 

 in water, for example. It does not in this case produce 

 flame or fire, but it does produce heat which is capable 

 of accurate measurement. But the heat of zinc burnt 

 in water falls short of that produced in pure oxygen, 

 the reason being that to obtain its oxygen from the 

 water the zinc must first dislodge the hydrogen. It is 

 in the performance of this molecular work that the 

 missing heat is absorbed. Mix the liberated hydrogen 

 with oxygen and cause them to recombine ; the heat 

 developed is mathematically equal to the missing heat. 

 Thus in pulling the oxygen and hydrogen asunder an 

 amount of heat is consumed which is accurately restored 

 by their reunion. 



This leads up to a few remarks upon the Voltaic 

 battery. It is not my design to dwell upon the technical 

 features of this wonderful instrument, but simply, by 

 means of it, to show what varying shapes a given 



