A DISTINGUISHED philosopher said recently, possibly
with a touch of impatience, that in the discussions of
modern physicists matter evaporates into a set of
equations. And certainly every student of physics very
soon notes that he has far less in the laboratory to do
with matter than in the outside world. From the
beginning of his study his attention is directed to
stresses, tensions, straight and curvilinear motions,
positive and negative accelerations, vibrations, waves,
electric charges, capacities and masses. That any of
these are physical substances would hardly be asserted
by even the stoutest materialist. They are neutral
concepts all, and are all dealt with by pretty, mathe-
matical methods. Such a student, however, used to be
reassured and convinced that he was really after all
studying matter, and not pure mathematics, by the
statement of his teacher that the world about him con-
sisted of very small particles of matter (conceived after
the analogy of microscopic tennis-balls), and that it was
these that possessed the mass, suffered the tensions and
motions, and bore the electric charges. He was taught
to call them atoms. And some fifty years ago there was
very little more for him to learn in this connection.
To-day the situation is different.

-115-