24 FRAGMENTS OF SCIENCE 



sions, and the less is the living force. Now the principle 

 of conservation affirms, not the constancy of the value of 

 the tensions of gravity, nor yet the constancy of the vis 

 viva, taken separately, but the absolute constancy of the 

 value of both taken together. At the beginning the vis 

 viva was zero, and the tension area was a maximum; close 

 to F the vis viva is a maximum, while the tension area is 

 zero. At every other point, the work- producing power 

 of the particle D consists in part of vis viva, and in part 

 of tensions. 



If gravity, instead of being attraction, were repulsion, 

 then, with the particles in contact, the sum of the tensions 

 between D and F would be a maximum, and the vis viva 

 zero. If, in obedience to the repulsion, D moved away 

 from F, vis viva would be generated; and the further D 

 retreated from F the greater would be its vis viva, and the 

 less the amount of tension still available for producing 

 motion. Taking repulsion as well as attraction into ac- 

 count, the principle of the conservation of force affirms 

 that the mechanical value of the tensions and vires vivce of 

 the material universe, so far as we know it, is a constant 

 quantity. The universe, in short, possesses two kinds of 

 property which are mutually convertible. The diminution 

 of either carries with it the enhancement of the other, the 

 total value of the property remaining unchanged. 



The considerations here applied to gravity apply 

 equally to chemical affinity. In a mixture of oxygen 

 and hydrogen the atoms exist apart, but by the applica- 

 tion of proper means they may be caused to rush together 

 across the space that separates them. While this space 

 exists, and as long as the atoms have not begun to move 

 toward each other, we have tensions and nothing else. 



