ttention.
Standing upon one of, the London bridges, we observe the current of
the Thames reversed, and the water poured upward twice a-day. The
water thus moved rubs against the river's bed, and heat is the
consequence of this friction. The heat thus generated is in part
radiated into space and lost, as far as the earth is concerned. What
supplies this incessant loss? The earth's rotation. Let us look a
little more closely at the matter. Imagine the moon fixed, and the
earth turning like a wheel from west to east in its diurnal rotation.
Suppose a high mountain on the earth's surface approaching the earth's
meridian; that mountain is, as it were, laid hold of by the moon; it
forms a kind of handle by which the earth is pulled more quickly
round. But when the meridian is passed the pull of the moon on the
mountain would be in the opposite direction, it would tend to diminish
the velocity of rotation as much as it previously augmented it; thus
the action of all fixed bodies on the earth's surface is neutralised.
But suppose the mountain to lie always to the east of the moon's
meridian, the pull then would be always exerted against the earth's
rotation, the velocity of which would be diminished in a degree
corresponding to the strength of the pull. _The tidal wave occupies
this position_--it lies always to the east of the moon's meridian. The
waters of the ocean are in part dragged as a brake along the surface
of the earth; and as a brake they must diminish the velocity of the
earth's rotation. [Footnote: Kant surmised an action of this kind.]
Supposing then that we turn a mill by the action of the tide, and
produce heat by the friction of the millstones; that heat has an
origin totally different from the heat produced by another mill which
is turned by a mountain stream. The former is produced at the expense
of the earth's rotation, the latter at the expense of the sun's
radiation.

The sun, by the act of vaporisation, lifts mechanically all the
moisture of our air, which when it condenses falls in the form of
rain, and when it freezes falls as snow. In this solid form it is
piled upon the Alpine heights, and furnishes materials for glaciers.
But the sun again interposes, liberates the solidified liquid, and
permits it to roll by gravity to the sea. The mechanical force of
every river in the world as it rolls towards the ocean, is drawn from
the heat of the sun. No streamlet glides to a lower level without
h