Ill SCIENCE AND PSEUDO-SCIENCE 113 



polling force " out of which the necessity arises ; 

 and further, if it is not necessary, whether it loses 

 the character of a law of nature ? 



I take it to be a law of nature, based on unex- 

 ceptionable evidence, that the mass of matter 

 remains unchanged, whatever chemical or other 

 modifications it may undergo. This law is one of 

 the foundations of chemistry. But it is by no 

 means necessary. It is quite possible to imagine 

 that the mass of matter should vary according to 

 circumstances, as we know its weight does. More- 

 over, the determination of the " force " which 

 makes mass constant (if there is any intelligi- 

 bility in that form of words) would not, so far as 

 I can see, confer any more validity on the law 

 than it has now. 



There is a law of nature, so well vouched by 

 experience, that all mankind, from pure logicians 

 in search of examples to parish sextons in search 

 of fees, confide in it. This is the law that " all 

 men are mortal." It is simply a statement of 

 the observed order of facts that all men sooner or 

 later die. I am not acquainted with any law of 

 nature which is more "constant and uniform" 

 than this. But will any one tell me that death is 

 " necessary " ? Certainly there is no a priori 

 necessity in the case, for various men have been 

 imagined to be immortal. And I should be glad 

 to be informed of any " necessity " that can be 

 deduced from biological considerations. It is 



