1888. | NEW YORK ACADEMY OF SCIENCES. 203 
During the years 1780 to 1785, pneumatic chemistry was the 
principal topic under discussion, for Priestley and Watt were each 
contributing his share to the much-vexed question of the consti- 
tution of water. Cavendish in London, Lavoisier in Paris, and 
Watt in Birmingham were three rival claimants for the honor 
of the discovery of the composition of water. Priestley, asa friend 
of Watt, communicated speedily the results of his experiments, 
sometimes it is reasonable to believe, over the festive board of the 
Lunarians, and left the conclusions to be drawn by others. As 
to the relative merits of the claimants, that is foreign to the 
purpose of this essay. 
The Priestley-Wedgwood correspondence’ shows that in 1783 
the philosophers were greatly exercised over Priestley’s discovery 
of theconversion of water intoair, the fallacy of which he himself 
afterwards admitted. 
The Phlogistic Theory, which had been the controlling spirit 
in chemical philosophy for nearly a century, received its death- 
blow at the hands of Priestley himself, when he isolated oxygen 
on the 1st August, 1774. But he, as is well known, failed to per- 
ceive the important bearing of his own discovery, and it was 
across the channel that Lavoisier and other French chemists 
were skilfully burying the corpse out of sight. The French 
theory of combustion was but slowly accepted by conservative 
Englishmen, and slowest of all by the friends of Priestley. 
In the transition period, hydrogen was for a time believed to 
be the elusive phlogiston; to this phase of doctrine, Boulton 
alludes in a letter to Wedgwood dated March 30th, 1781. 
‘‘ We have long talked of phlogiston without knowing what 
we talked about; but now that Dr. Priestley hath brought the 
matter to light, we can pour that element out of one vessel into 
another, can tell how much of it by accurate measurement is 
necessary to reduce a calx to a metal, which is easily done, and 
without putting that calx into contact with any visible thing. 
In short, this goddess of levity can be measured and weighed 
like other matter. For the rest, I refer you to the doctor him- 
self.” 
A few months later, Priestley himself wrote to his friend, 
Josiah Wedgwood: ‘‘ Before my late experiments, phlogiston was 
indeed almost given up by the Lunar Society, but now it seems 
to be re-established ” (March 21st, 1782), 
‘discrimination of unusual delicacy, enabled her, in after years, to 
record her souvenirs, Her mother was a most intimate friend of Mrs. 
Priestley, and William Priestley was a playmate in her youth. (‘‘ Life 
a Mary Ann Schimmel Penninck,” edited by C. C. Hankin. London, 
59.) 
1 See authorities at the close of this paper. 
