26 Life and Matter [chap. h. 



ward forms, yet that they themselves are 

 immutable and indestructible, constant in 

 number and quality and form, not subject 

 to any law of evolution ; in other words, 

 totally unaffected by time. 



If we ask for the evidence on which this 

 generalisation is founded, we have to appeal 

 to various delicate weighings, conducted 

 chiefly by chemists for practical purposes, 

 and very few of them really directed to 

 ascertain whether the law is true or not. 

 A few such direct experiments are now, 

 indeed, being conducted with the hope of 

 finding that the law is not completely true ; 

 in other words, with the hope of finding 

 that the weight of a body does depend 

 slightly on its state of aggregation or on some 

 other physical property. The question has 

 even been raised whether the weight of a 

 crystal is altogether independent of its aspect : 

 the direction of its plane of cleavage with 

 reference to the earth's radius ; also, whether 

 the temperature of bodies has any influence 

 on their weight ; but on these points it may 



