APPENDIX 361 



far apart from each other. Now the golf ball and 

 the earth; or the atoms of hydrogen and oxygen, 

 are physically the same material entities, whether 

 they are close together or far apart, yet when 

 the earth and the ball, or the atoms of oxygen and 

 hydrogen, are separated from each other, their " pro- 

 perties " are different from what they are when they are 

 close together. What is it that makes the difference ? 

 It is that which is between them. Is it, in the last case, 

 " the potential energy of chemical affinity " ? This 

 dreadful phrase is actually used in a recent book on 

 biology : "In the elements carbon and oxygen, so 

 long as they remain separate, a certain amount of 

 energy remains latent. When the carbon and oxygen 

 atoms are allowed to come together and unite, this 

 potential energy of chemical affinity is liberated as 

 kinetic energy/." What is changed by the tract at ion 

 and pellation (the terms suggested by Soddy in place 

 of the anthropomorphic ones, "attraction" and " re- 

 pulsion ") ? It is the ether which has become changed 

 in some way. Potential energy resides therefore in 

 the ether of space. 



ISOTHERMAL AND ADIABATIC CHANGES 



Let us consider the changes which occur in a gas 

 under the influence of changes in temperature and 

 pressure, premising that the remarks which we have 

 to make can be applied to bodies in the liquid and 

 solid conditions, with some necessary modifications. 

 A gas, then, consists of a very great number of particles, 

 or molecules, in motion. These molecules move in 

 straight lines at very high velocities, and if the envelope 

 in which the gas is contained is a restricted one, the 

 molecules collide with each other, and with the walls 



