Hitman Physiology. 83 



The atoms of gases are kept far apart by elastic repelling 

 forces, but, under certain conditions, they come nearer, as 

 when hydrogen unites with oxygen to form water ; and water 

 will dissolve salt, sugar, and other substances without much 

 increase of bulk. So solid a substance as gold will drink up 

 mercury as a sponge does water; but in this case the attraction 

 of the atoms of gold for each other is destroyed. The gold is 

 dissolved in mercury like salt in water. Heat the gold, so 

 as to drive off the mercury in vapour, and it resumes its solid 

 form. 



But a solid body is not really what we commonly conceive 

 of as solid. All matter is perhaps composed of molecules, or 

 assemblages of atoms; and we cannot conceive of matter but 

 as composed of atoms. A gas is matter with its atoms driven 

 far apart by their mutual repulsion, and moving freely and 

 almost independently of each other. Condense the gas bring 

 the atoms a thousand times, perhaps ten thousand times, nearer 

 together, and we have a free flowing liquid, where the atoms do 

 not interfere much with each other's motions, but dense, visible, 

 and tangible, bearing us up, like water. In what we call a 

 solid body, the atoms come still nearer to each other, and are 

 held by their mutual attractions and repulsions in fixed posi- 

 tions, but still they do not touch each other. No two atoms 

 in the universe ever touched each other. No two atoms 

 remain for an instant at the same distance from each other. 

 The atoms of iron, gold, glass; of the keen edge of knife or 

 lancet, the point of a needle, the angle of a diamond which 

 -cuts glass, are all equally distinct from each other, held in 

 their places by forces of which we shall speak hereafter. 



What is the proof? It is that all bodies expand by heat 

 that is, their atoms go further apart in all directions. They 

 contract with cold, or the diminution of heat; and they could 

 not do this if the atoms already touched each other. Tem- 

 perature changes every moment, and the diamond on a lady's 



