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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 instantaneous.

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The fact last referred to is very important.  The ice, in fact, is as it were automatically turned to water.  It is not a matter of the conduction of heat from point to point in the ice.  Its own sensible heat is immediately absorbed throughout the mass.  This would be the theoretical result, but it is probable that owing to imperfections throughout the ice and failure in uniformity in the distribution of the stress, the melting would not take place quite uniformly or homogeneously.

Before applying our new ideas to skating, I want you to notice a fact which I have inferentially stated, but not specifically mentioned.  Pressure will only lead to the melting of ice if the new melting point, i.e. that due to the pressure, is below the prevailing temperature.  Let us take figures.  The ice to start with is, say, at -3 deg.  C. Suppose we apply such a pressure to this ice as will confer a melting point of -2 deg.  C. on it.  Obviously, there will be no melting.  For why should ice which is at -3 deg.  C. melt when its melting point is -2 deg.  C.?  The ice is, in fact, colder than its melting point.  Hence, you note this fact:  The pressure must be sufficiently intense to bring the melting point below the prevailing temperature, or there will be no melting; and the further we reduce the melting point by pressure below the prevailing temperature, the more ice will be melted.

We come at length to the object of our remarks I don’t know who invented skating or skates.  It is said that in the thirteenth century the inhabitants of