upon one of the material facts by which that
beautiful theory is supported.

Here we have an instance of two men in the same university, discovering
latent heat, one wholly ignorant of the other's doings; fortunately, the
later discoverer only too glad to acknowledge and applaud the original,
and, strange to say, going to him to announce the discovery he had made.
Watt of course had no access to the Professor's classes, and some years
before the former stumbled upon the fact, the theory had been announced
by Black, but had apparently attracted little attention. This episode
reminds us of the advantages Watt had in his surroundings. He breathed
the very "atmosphere" of scientific and mechanical investigation and
invention, and had at hand not only the standard books, but the living
men who could best assist him.

What does latent heat mean? we hear the reader inquire. Let us try to
explain it in simple language. Arago pronounced Black's experiment
revealing it as one of the most remarkable in modern physics. Water
passed as an element until Watt found it was a compound. Change its
temperature and it exists in three different states, liquid, solid, and
gaseous--water, ice and steam. Convert water into steam, and pass, say,
two pounds of steam into ten pounds of water at freezing point and the
steam would be wholly liquified, _i.e._, become water again, at 212 deg.,
but the whole ten pounds of freezing water would also be raised to 212
deg. in the process. That is to say two pounds of steam will convert ten
pounds of freezing water into boiling water, so great is the latent heat
set free in the passage of steam to lower temperatures at the moment
when the contact of cold surfaces converts the vapor from the gaseous
into the liquid state. This heat is so thoroughly merged in the compound
that the most delicate thermometer cannot detect a variation. It is
undiscoverable by our senses and yet it proves its existence beyond
question by its work. Heat which is obtained by the combustion of coal
or wood, lies also in water, to be drawn forth and utilised in steam. It
is apparently a mere question of temperature. The heat lies latent and
dead until we raise the temperature of the water to 212 deg., and it is
turned to vapor. Then the powerful force is instantly imbued with life
and we harness it for our purposes.

The description of latent heat which gave the writer the clearest idea
of it, and at the same time a much-neede