LORD BROUGHAM’S APPENDIX. 477 
deprived of their latent heat, from the union of the bases 
of inflammable air and of dephlogisticated air; if this idea 
had been accompanied in their minds by as much clearness 
as in that of Lavoisier, they would certainly have avoided the 
uncertainty and obscurity which I have pointed out.* 
As far as relates to Watt, the following are the new facts 
that we have succeeded in establishing. 
1. There is no proof that anybody had given, in a written 
document, anterior to Watt, the present theory of the compo- 
sition of water. . 
2.) Watt established this theory during the year 1783, in 
* At the foot of p. 333, of the Transactions (for 1784), in a part of 
his April letter, 1783, printed in italics, Watt said: ‘ Are we not 
then authorized to conclude that water is composed of dephlogisti- 
cated air and phlogiston deprived of part of their latent or elemen- 
tary heat; that dephlogisticated air, or pure air, is composed of water 
deprived of its phlogiston and united to elementary heat and light; 
that heat and light are contained in it in a latent state, since they do 
not affect either the thermometer or the eye? If light is only a modi- 
fication of heat, or a peculiarity in its existence, or a constituent part 
of inflammable air, then pure or dephlogisticated air is composed of 
water deprived of its phlogiston, and united to some elementary 
heat.’’ 
Is not this passage as clear, precise, and intelligible as Lavoisier’s 
conclusions ?—( Note by Mr. Watt, jun.) 
The obscurity complained of by Lord Brougham in the theoretical 
conceptions of Watt and of Cavendish appears to me unfounded. In 
1784 they knew how to prepare two permanent and very dissimilar 
gases. Those two gases were by some distinguished as pure air and 
inflammable air; by others as dephlogisticated air and phlogiston; 
by others, finally, as oxygen and hydrogen. By the combination of 
dephlogisticated air and phlogiston, they generated water weighing 
as much as the two gases. Thenceforward water was no longer a 
simple body; it was composed of dephlogisticated air and phlogiston. 
The chemist who deduced this conclusion might have false ideas on 
the internal nature of phlogiston without its casting any uncertainty 
on the merit of his first discovery. Has it been even now mathemati- 
cally demonstrated that hydrogen (or phlogiston) is an elementary 
body; that it isnot, as Watt and Cavendish for a time supposed, the 
‘ combination of a radical with a little water ?—( Note by M. Arago.) 
