164 THE ANATOMY OF SCIENCE 



The natural pliilosophers of a few generations 

 ago spoke of "imponderable substances" such 

 as heat, light and electricity, but all these are 

 now known to possess some weight. The fact is 

 that in the complex domain which we are now 

 entering we cannot afford to be disturbed by 

 such verbal imperfections; there are too many 

 other things to think about. The science of dy- 

 namics grew out of the study of just one prop- 

 erty of matter, its mass or weight, ignoring the 

 hundreds of other properties which it exhibits. 

 But we do not go very far toward describing a 

 humming-bird when we say that it weighs ten 

 grams. 



In the great variety of properties that vari- 

 ous materials exhibit it is necessary to look for 

 some traits of permanence or identity. It is 

 easy to discover that ice and water, despite their 

 dissimilarity, have something in common. So 

 also we discover that to the action of fire or 

 acids a statue of Praxiteles behaves like the 

 block of marble from which it was sculptured. 

 It is these intrinsic properties, which are inde- 

 pendent of external form and appearance, that 

 serve for the classification of the different sub- 

 stances of which chemistry has analyzed and 

 classified perhaps two hundred thousand, and 



