28 THE INFLUENCE OF ENVIRONMENT ON 



pressure is increased beyond the normal amount we 

 find that the water will remain liquid at a tempera- 

 ture at which it would previously have assumed the 

 solid form of ice. 



Let us take another example from Chemistry. 

 Chemical formulae have a very definite appearance, 

 yet every chemist knows well that the reactions 

 they indicate will only occur provided certain 

 conditions of environment be fulfilled, especially 

 those of temperature and pressure ; and that a 

 change of no great extent in environment may cause 

 either a completely different reaction or even an 

 actual reversal of the previous action. For in- 

 stance, Mercury at 300 C. combines with oxygen to 

 form oxide of mercury ; now if the temperature is 

 raised to 400 C. this action is reversed. 



I have purposely chosen simple and familiar 

 examples in order to illustrate with as little loss of 

 time as possible what we mean by environment. The 

 points to which I wish to direct attention are these: 

 Firstly, that the actual condition of any body may 

 be regarded as the resultant of the several forces 

 acting on it at the time ; secondly, that therefore, 

 if we know all the conditions of environment, we can 

 calculate with certainty the actual condition of the 

 body ; thirdly, that a change of known amount in 

 one of the elements of the environment will produce 

 a definite and calculable change in the conditions 

 of the body acted on. In other words, that not 

 only has environment a marked and definite action, 

 but that this action is capable of exact measurement. 



Now let me turn to the more immediate subject 



