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
principles 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 be left over, if such there should be. It is hence supposed that
matter is composed 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 amongst
substances for each other's company. One will remain combined in
solution with another, till a third is added, when it will abandon
the former and attach itself to the latter. A fourth being added,
the third will perhaps leave the first, and join the new comer.

Such is an outline of the information which chemistry gives us
regarding the constituent materials of our globe. How infinitely is