IV 



Matter in Motion 



FROM geometry we proceeded to the larger 

 science of kinematics, which includes ge- 

 ometrical measurements and measurements of 

 time as well. Just as we employ geometry in the 

 practice of mensuration without regard to the 

 composition or the intrinsic properties of the 

 objects measured, so in kinematics we are deal- 

 ing with the laws of abstract motion without 

 caring what it is that moves. If we now wish to 

 enlarge this science still further, so as to in- 

 clude not only space and time, but some other 

 measured quantity, we seek among the count- 

 less properties of natural objects some one 

 property which they all possess and which seems 

 suitable for the purpose. The property so 

 chosen by the pioneers in science is the one we 

 now call mass, and the general science which 

 results is called mechanics. 



The choice was by no means compulsory. 

 Electric charge, for example, is a very impor- 

 tant property, and the great science of electro- 

 magnetics can be built up out of the concept 

 of space and time and electric charge without 



