d to solid friction in
the machine here automatically call the lubricant into
existence.

Just under the edge of the skate the pressure is enormous.
Consider that the whole weight of the skater is born upon a mere
knife edge. The skater alternately throws his whole weight upon
the edge of each skate. But not only is the weight thus
concentrated upon one edge, further concentration is secured in
the best skates by making the skate hollow-ground, _i.e._
increasing the keenness of the edge by making it less than a
right angle. Still greater pressure is obtained by diminishing
the length of that part of the blade which is in contact with the
ice. This is done by putting curvature on the blade or making it
what is called "hog-backed." You see that everything is done to
diminish the area in contact with the ice, and thus to increase
the pressure. The result is a very great compression of the ice
beneath the edge of the skate. Even in the very coldest weather
melting must take place to some extent.

As we observed before, the melting is instantaneous,

275

Heat has not to travel from one point of the ice to another;
immediately the pressure comes on the ice it turns to water. It
takes the requisite heat from itself in order that the change of
state may be accomplished. So soon as the skate passes on, the
water resumes the solid state. It is probable that there is an
instantaneous escape, and re-freezing of some of the water from
beneath the skate, the skate instantly taking a fresh bearing and
melting more ice. The temperature of the water escaping from
beneath the skate, or left behind by it, immediately becomes what
it was before the skate pressed upon it.

Thus, a most wonderful and complex series of molecular events
takes place beneath the skate. Swift as it passes, the whole
sequence of events which James Thomson predicted has to take
place beneath the blade Compression; lowering of the melting
point below the temperature of the surrounding ice; melting;
absorption of heat; and cooling to the new melting point, _i.e._
to that proper to the pressure beneath the blade. The skate now
passes on. Then follow: Relief of pressure; re-solidification of
the water; restoration of the borrowed heat from the congealing
water and reversion of the ice to the original temperature.

If we reflect for a moment on all this, we see that we do not
skate on ice but on water. We could not skate on ice any more
than we could skate o