cation of heat to the body of liquefied ice be
continued, the column of mercury will resume its movement upward until
it reaches the boiling point, where it is again arrested. And no matter
how much heat is applied to the boiling water, if in an open vessel, the
thermometer remains the same until all the water is evaporated. Here are
two curious facts, and they are facts that, if we can master them, will
serve as a key to the understanding of much that is mysterious in
nature.

It will be our endeavor to give the reader a mental picture of what is
taking place during the time the ice is melting and the thermometer is
stationary. Do not suppose that you can understand this, even so far as
it is understandable, by a casual reading without thought. No man was
ever yet able to present a picture to the mind of another, however
clearly and simply it may be done, unless that other mind is receptive.
When a photographer trains his camera upon an object, however intense
the light may be and however clean-cut the picture that is thrown upon
the plate in the camera, unless that plate is properly sensitized so
that the picture may be impressed upon it, all of the other conditions
are in vain. The reader is always a part of the book he is reading.

CHAPTER XXIII.

STORED ENERGY IN WATER.

In our last chapter we traced the upward movement in the mercury of the
thermometer from 10 degrees below the freezing point up to the boiling
point of water. We found that the thermometer was arrested at 32 degrees
and remained stationary at that point until all the ice was melted,
notwithstanding the fact that heat was being constantly applied. After
the ice is all melted the mercury moves upward until it reaches the
boiling point of water, where the movement is again arrested, and
although the heat is being continuously applied, it remains stationary
until all the water is evaporated. If we push the process still further,
with a sufficient application of energy we can separate the vapor
molecules into their original elements, oxygen and hydrogen.

Let us go back now to the freezing point of water and see what is
becoming of the heat that is consumed in melting the cake of ice, and
still does not produce any effect upon the mercury in the thermometer.
Sensible heat, as before stated, is a movement of the atoms of matter,
and temperature, as it affects the thermometer, is a measure of the
intensity of motion exhibited by these atoms.