ins my hypothesis. It is not
founded on so brittle a basis as an earthen retort, nor on _its_
converting water into air. I founded it on the other facts, and
was obliged to stretch it a good deal before it would fit this
experiment.... I maintain my hypothesis until it shall be shown
that the water formed after the explosion of the pure and
inflammable airs, has some other origin.

He also writes to Mr. DeLuc on May 18th:

I do not see Dr. Priestley's experiment in the same light that
he does. It does not disprove my theory.... My assertion was
simply, that air (_i.e._, dephlogisticated air, or oxygen,
which was also commonly called vital air, pure air, or simple
_air_) was water deprived of its phlogiston, and united to heat,
which I grounded on the decomposition of air by inflammation
with inflammable air, the residuum, or product of which, is only
water and heat.

Having, by experiments of his own, fully satisfied himself of the
correctness of his theory, in November he prepared a full statement for
the Royal Society, having asked the society to withhold his first paper
until he could prove it for himself by experiment. He never doubted its
correctness, but some members of the society advised that it had better
be supported by facts.

When the discovery was so daring that Priestley, who made the
experiments, could not believe it and had to be convinced by Watt of its
correctness, there seems little room left for other claimants, nor for
doubt as to whom is due the credit of the revelation.

Watt encountered the difficulties of different weights and measures in
his studies of foreign writers upon chemistry, a serious inconvenience
which still remains with us.

He wrote Mr. Kirwan, November, 1783:

I had a great deal of trouble in reducing the weights and
measures to speak the same language; and many of the German
experiments become still more difficult from their using
different weights and different divisions of them in different
parts of that empire. It is therefore a very desirable thing to
have these difficulties removed, and to get all philosophers to
use pounds divided in the same manner, and I flatter myself that
may be accomplished if you, Dr. Priestley, and a few of the
French experimenters will agree to it; for the utility is so
evident, that every thinking person must immediately be
convinced of it.