lectric current, so that it will be seen
that we are moving into the direction of the continuity of Matter. Let
us now look at the question as to what is meant by an atom more fully.

ART. 32. _What is an Atom?_--Clerk Maxwell's definition of an atom is,
"a body that cannot be cut in two." An atom is the smallest part of a
simple substance which can enter into combination with another element,
and is incapable of being further subdivided.

An atom of hydrogen is the smallest part of that particular gas which
can enter into combination with any other element, as oxygen, to form a
chemical compound as water, which is composed of two atoms of hydrogen
and one of oxygen.

Further, an atom of any kind or sort, retains its identity and remains
the same throughout all chemical combinations or physical changes which
it may undergo. By spectroscopic analysis, it has been ascertained, for
example, that hydrogen exists in the sun and stars, and the conclusion
is arrived at in connection therewith, that an atom of hydrogen in any
sun or star is the same as an atom of hydrogen in our atmosphere, or in
any of the compounds, as water, in which it is found. Thus it has come
to be received as an accepted fact, that every atom of any substance, as
oxygen, nitrogen, and hydrogen, whether they exist in the earth or sun,
in meteorites or the farthest stars or nebulae, wherever they are found,
possesses the same identity and the same physical properties.

Atoms attract one another, and this atomic attraction is known as
affinity. There is not the least possible doubt that affinity is a form
of universal attraction, except that the affinity of atoms is selective.
This affinity of atoms for each other gives rise to the combination of
atoms known as molecules and chemical compounds.

_Size of Atoms._--It has been computed by Lord Kelvin and others, that
an atom may be as small as 1/50,000,000 of an inch in diameter, so that
if 50,000,000 of them were put side by side, they would just measure one
inch in length. Atoms are not all of the same size or weight. An atom of
oxygen weighs 16 times as much as an atom of hydrogen. It has been
proved by Kirchhoff and Bunsen, that the 3/1,000,000 part of a
milligramme of sodium chloride is sufficient to give a yellow colour to
a gas-jet. Faraday prepared some sheets of gold, so thin that he
estimated they only measured the 1/100 part of the length of a
light-wave. We have to remember that each sheet