rake upon the wheels.
The translatory energy of the train is transformed into the molecular
energy called heat. The steamship requires to propel it fast, a large
amount of coal for its engines, because the water in which it moves
offers great friction--resistance which must be overcome. Whenever one
surface of matter is moved in contact with another surface there is a
resistance called friction, the moving body loses its rate of motion,
and will presently be brought to rest unless energy be continuously
supplied. This is true for masses of matter of all sizes and with all
kinds of motion. Friction is the condition for the transformation of all
kinds of mechanical motions into heat. The test of the amount of
friction is the rate of loss of motion. A top will spin some time in the
air because its point is small. It will spin longer on a plate than on
the carpet, and longer in a vacuum than in the air, for it does not have
the air friction to resist it, and there is no kind or form of matter
not subject to frictional resistance.

THE ETHER IS FRICTIONLESS.

The earth is a mass of matter moving in the ether. In the equatorial
region the velocity of a point is more than a thousand miles in an hour,
for the circumference of the earth is 25,000 miles, and it turns once on
its axis in 24 hours, which is the length of the day. If the earth were
thus spinning in the atmosphere, the latter not being in motion, the
wind would blow with ten times hurricane velocity. The friction would be
so great that nothing but the foundation rocks of the earth's crust
could withstand it, and the velocity of rotation would be reduced
appreciably in a relatively short time. The air moves along with the
earth as a part of it, and consequently no such frictional destruction
takes place, but the earth rotates in the ether with that same rate, and
if the ether offered resistance it would react so as to retard the
rotation and increase the length of the day. Astronomical observations
show that the length of the day has certainly not changed so much as the
tenth of a second during the past 2000 years. The earth also revolves
about the sun, having a speed of about 19 miles in a second, or 68,000
miles an hour. This motion of the earth and the other planets about the
sun is one of the most stable phenomena we know. The mean distance and
period of revolution of every planet is unalterable in the long run. If
the earth had been retarded by its friction in