ous stories he heard concerning
the growth of metals in previously exhausted mines, he believed that the
air was responsible for producing this growth--in which he undoubtedly
believed. The story of a tin-miner that, in his own time, after a lapse
of only twenty-five years, a heap, of earth previously exhausted of
its ore became again even more richly impregnated than before by lying
exposed to the air, seems to have been believed by the philosopher.

As Boyle was an alchemist, and undoubtedly believed in the alchemic
theory that metals have "spirits" and various other qualities that do
not exist, it is not surprising that he was credulous in the matter of
beliefs concerning peculiar phenomena exhibited by them. Furthermore,
he undoubtedly fell into the error common to "specialists," or
persons working for long periods of time on one subject--the error of
over-enthusiasm in his subject. He had discovered so many remarkable
qualities in the air that it is not surprising to find that he
attributed to it many more that he could not demonstrate.

Boyle's work upon colors, although probably of less importance than his
experiments and deductions upon air, show that he was in the van as far
as the science of his day was concerned. As he points out, the schools
of his time generally taught that "color is a penetrating quality,
reaching to the innermost part of the substance," and, as an example
of this, sealing-wax was cited, which could be broken into minute bits,
each particle retaining the same color as its fellows or the original
mass. To refute this theory, and to show instances to the contrary,
Boyle, among other things, shows that various colors--blue, red,
yellow--may be produced upon tempered steel, and yet the metal within "a
hair's-breadth of its surface" have none of these colors. Therefore,
he was led to believe that color, in opaque bodies at least, is
superficial.

"But before we descend to a more particular consideration of our
subject," he says, "'tis proper to observe that colors may be
regarded either as a quality residing in bodies to modify light after a
particular manner, or else as light itself so modified as to strike upon
the organs of sight, and cause the sensation we call color; and that
this latter is the more proper acceptation of the word color will appear
hereafter. And indeed it is the light itself, which after a certain
manner, either mixed with shades or other-wise, strikes our eyes and
imme