478 JAMES WATT. 
more distinct terms than Cavendish did in his Memoir read to 
the Royal Society in January, 1784. By noticing also the 
disengagement of latent heat in the operation, Watt added 
very much to the clearness of his conception. 
8. There is no proof, there is not even any assertion 
whence it would result, that the theory of Cavendish (Blag- 
den calls it conclusion) was communicated to Priestley pre- 
viously to Watt’s delivering his ideas in the letter of the 26th 
of April, 1783; and still more, nothing leads one to suppose, 
especially after reading Watt’s letter, that he had ever heard 
any thing relative to the composition of water either from 
Priestley or from any other person. 
4. Watt’s theory was known by the Fellows of the Royal 
Society several months before the conclusions of Cavendish 
had been committed to paper; eight months before the Me~ 
moir of that chemist was presented to that same Society. We 
can go farther, and deduce from facts and dates now before us, 
that Watt was the first to speak of the composition of water ; 
that if any one was anterior to him, there is no proof of it. 
5. Finally, a repugnance to abandon the doctrine of phlo- 
giston, a sort of timidity in separating from an opinion so long 
established, so deeply rooted, prevented Watt and Cavendish 
from rendering complete justice to their own theory; whilst 
Lavoisier, who had broken through those trammels, was the 
first to present the new doctrine in all its perfection.* 
It might be very possible that without knowing any thing of 
their respective labours, Watt, Cavendish, and Lavoisier had 
nearly at the same time made the great step of concluding 
from experiment, that water is the product of a combination 
* No one ought to have expected from Watt, writing and publish- 
ing for the first time, exposed to the cares of an immense manufac- 
tory and of commercial affairs equally extensive, that he could vie 
with the eloquent and practised pen of Lavoisier; but the substance 
of his theory (see p. 333 of his Memoir) seems, at least to me, who in 
truth may not perhaps be an impartial judge, as luminous and as 
remarkable in expression as the conclusions of the illustrious French 
chemist.—(Note by Mr. Watt, jun.) 
