228 DANGEROUS THOUGHTS

with wood, as being a worse conductor of heat than the brick-
work which surrounds the common furnaces, and he cased the
cylinders and all the conducting pipes in materials which con-
ducted heat very slowly. But none of these contrivances were
effectual, for it turned out that the chief expenditure of steam and
consequently of fuel in the Newcomen engine was occasioned by
the re-heating of the cylinder after the steam had been condensed
by the cold water admitted into it. Nearly four-fifths of the
whole steam employed was condensed on itr first admission, before
the surplus could act upon the piston.

Two features of Black's relation to Watt merit comment. One
is emphasized by Dickinson, who Dwells on the close friendship
between Bkck and Roebuck in his recently published book on
Boulton. Dickinson tells us that Black lent ^1,000 to Watt for
the conduct of his original experiments to make a working model
of an engine to use full steam pressure. The other is that no account
of his doctrine of latent heat announced in a paper to the New-
tonian Society about the year 1763 was ever printed by the
author. In a different social context we may wonder whether his
contemporary, Hutton, would have referred to it with such
eloquence in the opening chapter of his book, The Theory of
the Earth. Hutton there anticipates the conservation of energy,
when he says:

In the abstract doctrine of latent heat the ingenuity of man has
discovered a certain measure for the quantity of those commutable
effects which are perceived.

The following citation from Prosser's book on Birmingham
inventions discloses the direct influence of Watt on the subsequent
development of Black's contributions to thermal equilibrium.
Referring to John Southern, a Fellow of the Royal Society, at
a time when the Soho firm numbered four such among its per-
sonnel, Prosser says:

His researches on the elasticity, density and latent heat of steam
which were undertaken at Watt's request in 1803, were for a long
time the standard authority on the subject. They are printed in
Brewster's edition of Robison's mechanical philosophy.