rvature in the direction of the rays, he concluded, after thorough
reflection, that light is not _homogeneous_, but that it consists of
rays of diverse refrangibility. The red hue he saw was less refracted
than the orange, the orange less refracted than the yellow, and the
violet more than any of the rest. These important conclusions he applied
in the construction of the first reflecting telescope ever used in the
survey of the heavens, and an instrument is preserved in Trinity College
Library bearing the inscription, "Invented by Sir Isaac Newton, and made
with his own hands, 1671."

At the request of the Royal Society, he published in the "Transactions"
an account of his optical discoveries, and proved that white light is a
compound of seven prismatic colors.

Everybody is familiar with the story of Newton's watching the apple fall
from the tree. The tradition is fondly cherished on the spot where the
philosopher is said to have been struck by the fact. The _law_ by which
the apple falls, not the _reason_ which underlies the law, formed the
subject of Newton's reflections, and led to the grandest of modern
discoveries. The unknown cause of the apple's descent is the unknown
cause of the planet's motion. That was the truth, simple and grand,
which he brought to light and inculcated on the world. He undertook long
calculations which he expected would prove this theory, but they failed
to give the desired result. He consequently for a time desisted from the
inquiry and turned his attention to other subjects. The error in
Newton's first calculation arose from his taking the radius of the earth
according to the received notion that a degree measured sixty miles,
whereas Picard had determined it to be sixty-nine and a half miles. This
was mentioned at a meeting of the Royal Society in 1682, at which Newton
was present. "It immediately struck him that the value of the earth's
radius was the erroneous element in his first calculation. With a
feverish interest in this result, little imagined by those present, he
hurried home, resumed his calculation with the new value, and having
proceeded some way in it, was so overpowered by nervous agitation at its
anticipated result, that he was unable to go on, and requested a friend
to finish it for him, when it came out, _exactly establishing the
inverse square_ as the true measure of the moon's gravitation, and thus
furnishing the key to the whole system." Hence proceeded Newton's
imm