diately produces that motion in the organ which gives us the color
of an object."(6)

In examining smooth and rough surfaces to determine the cause of their
color, he made use of the microscope, and pointed out the very obvious
example of the difference in color of a rough and a polished piece of
the same block of stone. He used some striking illustrations of the
effect of light and the position of the eye upon colors. "Thus the color
of plush or velvet will appear various if you stroke part of it one way
and part another, the posture of the particular threads in regard to the
light, or the eye, being thereby varied. And 'tis observable that in a
field of ripe corn, blown upon by the wind, there will appear waves of a
color different from that of the rest of the corn, because the wind, by
depressing some of the ears more than others, causes one to reflect more
light from the lateral and strawy parts than another."(7) His work upon
color, however, as upon light, was entirely overshadowed by the work of
his great fellow-countryman Newton.

Boyle's work on electricity was a continuation of Gilbert's, to which he
added several new facts. He added several substances to Gilbert's list
of "electrics," experimented on smooth and rough surfaces in exciting
of electricity, and made the important discovery that amber retained its
attractive virtue after the friction that excited it bad ceased. "For
the attrition having caused an intestine motion in its parts," he says,
"the heat thereby excited ought not to cease as soon as ever the rubbing
is over, but to continue capable of emitting effluvia for some time
afterwards, longer or shorter according to the goodness of the electric
and the degree of the commotion made; all which, joined together, may
sometimes make the effect considerable; and by this means, on a warm
day, I, with a certain body not bigger than a pea, but very vigorously
attractive, moved a steel needle, freely poised, about three minutes
after I had left off rubbing it."(8)

MARIOTTE AND VON GUERICKE

Working contemporaneously with Boyle, and a man whose name is usually
associated with his as the propounder of the law of density of
gases, was Edme Mariotte (died 1684), a native of Burgundy. Mariotte
demonstrated that but for the resistance of the atmosphere, all bodies,
whether light or heavy, dense or thin, would fall with equal rapidity,
and he proved this by the well-known "guinea-and-feather" experiment.
Ha