cate series of experiments, verified in
every respect.

Suppose we had nothing but solid ice in the vessel at starting,
would the experiment result in the same way? Yes, it assuredly
would. The ice under the increased pressure would melt a little
everywhere throughout its mass, taking the requisite latent heat
from itself at the expense of its sensible heat, and the
temperature of the ice would fall to the new melting point.

Could we melt the whole of the ice in this manner? Again the
answer is "yes." But the pressure must be very great. If we
assume that all the heat is obtained at the expense of the
sensible heat of the ice, the cooling must be such as to supply
the latent heat of the whole mass of water produced. However, the
latent heat diminishes as the melting point is lowered, and at a
rate which would reduce it to nothing at about 18,000
atmospheres. Mousson, operating on ice enclosed in a conducting
cylinder and cooled to -18 deg. at starting

270

appears to have obtained very complete liquefaction. Mousson must
have attained a pressure of at least an amount adequate to lower
the melting point below -18 deg.. The degree of liquefaction actually
attained may have been due in part to the passage of heat through
the walls of the vessel. He proved the more or less complete
liquefaction of the ice within the vessel by the fall of a copper
index from the top to the bottom of the vessel while the pressure
was on.

I have here a simple way of demonstrating to you the fall of
temperature attending the compression of ice. In this mould,
which is strongly made of steel, lined with boxwood to diminish
the passage of conducted heat, is a quantity of ice which I
compress when I force in this plunger. In the ice is a
thermoelectric junction, the wires leading to which are in
communication with a reflecting galvanometer. The thermocouple is
of copper and nickel, and is of such sensitiveness as to show by
motion of the spot of light on the screen even a small fraction
of a degree. On applying the pressure, you see the spot of light
is displaced, and in such a direction as to indicate cooling. The
balancing thermocouple is all the time imbedded in a block of ice
so that its temperature remains unaltered. On taking off the
pressure, the spot of light returns to its first position. I can
move the spot of light backwards and forwards on the screen by
taking off and putting on the pressure. The effects are quite
instanta