80 ATOMS, MOLECULES, 



should combine in multiple proportions, and the out- 

 come and answer of this question is the atomic theory. 

 The definite weights of matter above referred to 

 represent the weights of atoms, indivisible by any force 

 which chemistry has hitherto brought to bear upon 

 them. If matter were a continuum if it were not 

 rounded off, so to say, into these discrete atomic masses 

 the impassable breaches of continuity which the law 

 of multiple proportions reveals could not be accounted 

 for. These atoms are what Maxwell finely calls * the 

 foundation-stones of the material universe,' which, amid 

 the wreck of composite matter, ' remain unbroken and 

 unworn.' 



A group of atoms drawn and held together by what 

 chemists term affinity, is called a molecule. The 

 ultimate parts of all compound bodies are molecules. 

 A molecule of water, for example, consists of two atoms 

 of hydrogen, which grasp and are grasped by one atom 

 of oxygen. When water is converted into steam, the 

 distances between the molecules are greatly augmented, 

 but the molecules themselves continue intact. We 

 must not, however, picture the constituent atoms of 

 any molecule as held so rigidly together as to render 

 intestine motion impossible. The interlocked atoms 

 have still liberty of vibration, which may, under certain 

 circumstances, become so intense as to shake the 

 molecule asunder. Most molecules probably all are 

 wrecked by intense heat, or in other words by intense 

 vibratory motion; and many are wrecked by a very 

 moderate heat of the proper quality. Indeed, a weak 

 force which bears a suitable relation to the constitution 

 of the molecule can, by timely savings and accumula- 

 tions, accomplish what a strong force out of such rela- 

 tion fails to achieve. 



We have here a glimpse of the world in which the 



