216 JVecessari/ Limitation of the Doctrine of the 



compression which is an essential property of matter itself. 

 So far as we know, it does not impart motion to the atom 

 at all, and has no relation either to motion, or to the space in 

 which the atom moves. It simply attends the particle and 

 occupies its internal mass. It is not called into operation by 

 any motion, mechanical or molecular, into which the particle 

 may be thrown. Moving, or at rest, the sole function which 

 we can recognize in it, or as belonging to it, is to preserve 

 the existence of the particle itself; and this.it does so effec- 

 tually that, as we have already seen, no particle is ever 

 destroyed, and the sum of them in the universe has never, 

 from the lirst, been diminished, by a single atom. 



Now it is an essential characteristic of this force that it is, 

 and must be, forever inconvertible into any other. For if 

 the force which guards the integrity, and guarantees the 

 permanent existence, of a particle, were convertible with any 

 other, it could not in its converted form perform its original 

 function ; and the atom might be converted into light, or 

 heat, or electricity. It might impart to other particles the 

 undulation Avhich constitutes light; but it could not do this, 

 and continue to resist compression, to which all matter is 

 perhaps subject. The atom would no longer be capable of 

 asserting itself by its normal resistance to external pressure, 

 and so, capable of maintaining its own existence ; and might 

 disappear forever in a flash of light. Matter deprived of the 

 force by which it is ultimately incompressible, would no 

 longer be indestructible ; its preservative force would be 

 gone ; and matter Avithout that preservative force which 

 arises from this power of resistance, would be inconceivable. 

 The fundamental fact or law of physics, that all matter is inde- 

 structible, implies that its essential force of resistance to com- 

 pression is inconvertible with any other. It exists unchanged 

 through all the chemical changes, through all the molecular 

 vibrations, or undulations, through all the mechanical trans- 

 fers, or movements of mass, which take place in the universe 

 around us; and it is forever incapable of being converted 



