staggering figures in the science of the
infinitely little that we do in the science of the infinitely vast. Thus
the physicist deals with a quantity of matter a million million times
smaller than can be detected in the most delicate chemical balance.
Molecules inconceivably small rush about in molecular space
inconceivably small. Ramsay calculates how many collisions the molecules
of gas make with other molecules every second, which is four and one
half quintillions. This staggers the mind like the tremendous
revelations of astronomy. Mathematics has no trouble to compute the
figures, but our slow, clumsy minds feel helpless before them. In every
drop of water we drink, and in every mouthful of air we breathe, there
is a movement and collision of particles so rapid in every second of
time that it can only be expressed by four with eighteen naughts. If the
movement of these particles were attended by friction, or if the energy
of their impact were translated into heat, what hot mouthfuls we should
have! But the heat, as well as the particles, is infinitesimal, and is
not perceptible.

II

The molecules and atoms and electrons into which science resolves matter
are hypothetical bodies which no human eye has ever seen, or ever can
see, but they build up the solid frame of the universe. The air and the
rocks are not so far apart in their constituents as they might seem to
our senses. The invisible and indivisible molecules of oxygen which we
breathe, and which keep our life-currents going, form about half the
crust of the earth. The soft breeze that fans and refreshes us, and the
rocks that crush us, are at least half-brothers. And herein we get a
glimpse of the magic of chemical combinations. That mysterious property
in matter which we call chemical affinity, a property beside which human
affinities and passions are tame and inconstant affairs, is the
architect of the universe. Certain elements attract certain other
elements with a fierce and unalterable attraction, and when they unite,
the resultant compound is a body totally unlike either of the
constituents. Both substances have disappeared, and a new one has taken
their place. This is the magic of chemical change. A physical change, as
of water into ice, or into steam, is a simple matter; it is merely a
matter of more or less heat; but the change of oxygen and hydrogen into
water, or of chlorine gas and the mineral sodium into common salt, is a
chemical change. In