34 VESTIGES OF THE 



metallic l)asis of alumina, a large material in many rocks, 

 is another abundant elementary substance. So, also, is 

 carbon a small ingredient in the atmosphere, but the 

 chief constituent of animal and vegetable substances, 

 and of all fossils which ever were in the latter condition, 

 amongst which coal takes a conspicuous place. The 

 familiarly known metals, as iron, tin, lead, silver, gold, 

 are elements of comparatively small magnitude in that 

 exterior part of the earth's body which we are able to 

 investigate. 



It is remarkable of the simple substances that they 

 are generally in some compound form. Thus, oxygen 

 and nitrogen, though in union they form the aerial 

 envelope of the globe, are never found separate in nature. 

 Carbon is pure only in the diamond. And the metallic 

 bases of the earths, though the chemist can disengage 

 them, may well be supposed unlikely to remain long 

 uncombined, seeing that contact with moisture makes 

 them burn. Combination and re-combination are prin- 

 ciples largely pervading nature. There are few rocks, 

 for example, that are not composed of at least two 

 varieties of matter, each of which is again a compound 

 of elementary substances. What is still more wonderful 

 with respect to this principle of combination, all the 

 elementary substances observe certain mathematical 

 proportions in their unions. One volume of them unites 

 with one, two, three, or more volumes of another, any 

 extra quantity being sure to bo left over, if such there 

 should be. It is hence supposed that matter is com- 

 posed of infinitely minute particles or atoms, each of 

 which belonging to any one substance, can only (through 

 the operation of some as yet hidden law) associate with 

 a certain number of the atoms of any other. There are 

 also strange predilections amonf^st substances for encli 



