THE FOUR ELEMENTS. 427 
tion, by some authorities which are not however so nu- 
merous as might be supposed; that you will not refuse 
to remark how few authors in the present day refer back 
to original sources ; how disagreeable they find it to dis- 
turb the dust of libraries; and, on the contrary, how con- 
venient to feed on the erudition of other people, to reduce 
the composition of a book to the mere work of editing. 
But the promise that I hold of your confidence in me, 
has appeared of more weight. I have pressed into my 
service a number of printed memoirs, the whole of a 
voluminous authentic correspondence still in manuscript ; 
and if after fifty years I come to claim for Watt an 
honour that has been inconsiderately granted to one of 
his most illustrious countrymen, it is because it has 
seemed to me beneficial to show that in the heart of 
academies, truth is sure to shine out sooner or later, and 
that in matters of discovery, there is never any pre- 
scription. 
The theory of the four pretended elements, fire, air, 
water, and earth, the varied combinations of which were 
to produce all known bodies, is one of the numerous lega- 
cies that have come down to us from the brilliant phil- 
osophy which, through several centuries, dazzled and 
misled some of the noblest intellects. Van Helmont 
was the first who shook, though slightly, one of the prin- 
ciples of this ancient theorem, by pointing out to the at- 
tention of chemists, various permanently elastic fluids, 
several sorts of air, that he called gases, the properties 
of which differed from those of common air, from those 
of the elemental air. Boyle’s and Hooke’s experiments 
raised more serious difficulties still: they prove that com- 
mon air, necessary to respiration and to combustion, un- 
dergoes remarkable changes in the course of those two 
