SCIENTIFIC METHOD 55 



annihilate it.' In order to realize the extent of the 

 imaginative swoop which the intellect of Mayer made in 

 formulating this conception, we have only to follow the 

 history of its birth, as set forth by Tyndall 1 . In the 

 summer of 1840 Mayer, practising medicine in Java, was 

 struck with the brighter red colour of the venous blood of 

 his patients. Reasoning on this he conceived it possible 

 that the brighter colour was due to less bodily oxidation 

 being necessary to keep up the body temperature in hot 

 climates. This drew his attention to animal heat, thence 

 to heat production in relation to mechanical work, and, 

 finally, to all forms of force. From extensive researches 

 along these lines he formulated the theory that through- 

 out the universe, both in the inorganic and the organic 

 world, there are forces which are convertible but are not 

 destructible. 



The theory has been extended since his day. Energy, 

 formerly termed force, is now conceived as modes of 

 motion ; differences in the mode affect our sense organs 

 so that we distinguish one as heat, others as light, elec- 

 tricity, chemical action, the movement of masses, gravity, 

 &c. We further postulate the existence of modes which are 

 unable to affect our sense organs ; these we can appreciate 

 when transformed into those modes which will affect us. 

 This motion is not in itself perceptible ; it is subtle, 

 occurring, for instance, in such a medium as the hypo- 

 thetical ether. Any given effect which its existence 

 produces upon our senses may cease as a stone ceases to 

 fall when it reaches the ground, or a lamp ceases to burn 

 when the oil is all consumed, but in accordance with the 

 conception of the conservation of energy there is no real 

 cessation of energy motion, there is only an alteration in 

 its mode ; thus the sum total remains for ever the same, 

 1 Tyndall, Fragments of Science, vol. i, ' The Copley Medalist of 1871.' 



