-1859] WRITINGS OF JOSEPH HENRY. 93 



atmosphere would fly from the earth by the repulsive energy 

 of its own atoms. We may therefore consider every atom 

 of matter endowed with the property of obedience to the laws 

 of force and motion;- with inertia, by which it cannot change 

 its place without the application of force, and when in motion 

 cannot stop this motion without the application of an equal 

 force in the opposite direction ; and with attraction and re- 

 pulsion, by which any two atoms placed at ever so great a dis- 

 tance from each other, will tend to approach each other with 

 a force increasing inversely as the square of the distance. 

 When these atoms approach very near to each other they 

 cease their motion, and if pressed nearer than this point 

 repel each other. And it appears from experiment and 

 observation that there are several alternations of attraction 

 and repulsion at distances too minute however for our senses, 

 and only indicated by certain phenomena. Repulsion exists 

 between the atoms of the densest bodies. Platinum, for ex- 

 ample, which is 21 times heavier than water, and 257,000 

 times heavier than hydrogen, is still condensable. It may 

 be compressed into a smaller space ; and since the shrinking 

 takes place equally in all directions, it follows that the atoms 

 of this substance, as well as those of all gross matter, are not 

 in contact. Indeed, when the hardest bodies are violently 

 impelled against each other, and each is indented by the 

 other, they do not come into actual mathematical contact, 

 but are mutually impressed by the repulsive energy, which, 

 vastly increased by the diminished distance, produces the 

 visible effect. 



All matter therefore is porous, whether in the gaseous, 

 liquid, or solid condition. The pores may be conceived to be 

 of different orders, namely, pores between the atoms, between 

 the molecules or assemblages of atoms, and between the still 

 larger particles. Gold itself is rendered brittle by being 

 exposed to the fumes of sulphur, and solid iron is converted 

 into steel by absorbing a large quantity of carbon, to which 

 inter-penetration it owes its quality of hardness. 



In the case of atmospheric air and other gases the repulsive 

 energy alone is exhibited in most of the mechanical phe- 



