ce of the grass into space, and to supply the
loss, there is a flow of heat from the earth to the blade. Thus the
blade loses heat by radiation, and gains heat by conduction. Now, in
the case before us, the power of radiation is great, whereas the power
of conduction is small; the consequence is that the blade loses more
than it gains, and hence becomes more and more refrigerated. The
light vapour floating around the surface so cooled is condensed upon
it, and there accumulates to form the little pearly globe which we
call a dew-drop.

Thus the boy finds the simple and homely fact which addressed his
senses to be the outcome and flower of the deepest laws. The fact
becomes, in a measure, sanctified as an object of thought, and
invested for him with a beauty for evermore. He thus learns that
things which, at first sight, seem to stand isolated and without
apparent brotherhood in Nature are organically united, and finds the
detection of such analogies a source of perpetual delight. To enlist
pleasure on the side of intellectual performance is a point of the
utmost importance; for the exercise of the mind, like that of the
body, depends for its value upon the spirit in which it is
accomplished. Every physician knows that something more than mere
mechanical motion is comprehended under the idea of healthful
exercise--that, indeed, being most healthful which makes us forget all
ulterior ends in the mere enjoyment of it. What, for example, could
be substituted for the action of the playground, where the boy plays
for the mere love of playing, and without reference to physiological
laws; while kindly Nature accomplishes her ends unconsciously, and
makes his very indifference beneficial to him. You may have more
systematic motions, you may devise means for the more perfect traction
of each particular muscle, but you cannot create the joy and gladness
of the game, and where these are absent, the charm and the health of
the exercise are gone. The case is similar with the education of the
mind.

The study of Physics, as already intimated, consists of two processes,
which are complementary to each other--the tracing of facts to their
causes, and the logical advance from the cause to the fact. In the
former process, called _induction_, certain moral qualities come into
play. The first condition of success is patient industry, an honest
receptivity, and a willingness to abandon all preconceived notions,
however cherish