[1] For particulars of the new technique and of some of the work
already accomplished, see papers, by Dr. Walter C. Stevenson,
_British Medical Journal_, July 4th, 1914, and March 20th, 1915.
259
SKATING [1]
IT is now many years ago since, as a student, I was present at a
college lecture delivered by a certain learned professor on the
subject of friction. At this lecture a discussion arose out of a
question addressed to our teacher: "How is it we can skate on ice
and on no other substance?"
The answer came back without hesitation: "Because the ice is so
smooth."
It was at once objected: "But you can skate on ice which is not
smooth."
This put the professor in a difficulty. Obviously it is not on
account of the smoothness of the ice. A piece of polished plate
glass is far smoother than a surface of ice after the latter is
cut up by a day's skating. Nevertheless, on the scratched and
torn ice-surface skating is still quite possible; on the smooth
plate glass we know we could not skate.
Some little time after this discussion, the connection between
skating and a somewhat abstruse fact in physical science occurred
to me. As the fact itself is one which has played a part in the
geological history of the earth,
[1] A lecture delivered before the Royal Dublin Society in 1905.
260