306 Answer to Observations ° 
thors who experimentally contradicts Dr. Priestley.” So far 
from this being the fact, it appears from the above quotations 
that he is endeavouring by all possible means to support him : 
indeed, the whole tenor of his work (so far from contradict= 
ing Dr. Priestley) is intended to corroborate the same. I will 
not occupy your pages by remarks on Scheele, Saussure, or 
Sennebier, but proceed to Mr. Ellis and Sir H. Davy. Your cor- 
respondent cannot approve more highly of the opinions enter- 
tained in the two volumes of the former of these authors than I 
do, But I think he again labours under a mistake when he 
represents Mr. Ellis’s second volume as the last work on the sub- 
ject ; for my copy bears the date of 1811. But that of Sir H. 
Davy on agricultural chemistry (which W. H. G. quotes) was 
published in 18183. Under these circumstances I know not by 
what means he can consider Mr. Ellis as the last author on the 
subject. But you will perceive that this is not merely the first, 
last, or greatest mistake W. H.G. has fallen into: for although 
Mr. Ellis has ably promulgated the same opinions (drawn from 
experiments differently conducted to what mine were) which I 
have since advanced; yet I think it is most unwarrantable and 
unjustifiable to represent “ Sir H. Davy as being convinced that 
Mr. Ellis had not been deceived by his extensive researches ;” 
and also of enrolling Sir H. in the list of half a dozen who had 
experimentally contradicted Dr. Priestley. In order to prove the 
error of the first statement, I must refer to Sir Humphry’s work 
above mentioned, p. 195, where Sir Humphry says, ** Some per- 
sons have supposed that plants exposed inthe free atmosphere 
to the vicissitudes of sun-shine and shade, light and darkness, 
consume more oxygen than they produce; and that their per- 
Manent agency upon air is similar to that of animals: and this 
opinion is espoused by the writer on the subject I have just 
quoted (Mr, Ellis), in his ingenious Researches on Vegetation. 
But all experiments brcught in favour of this idea, and particularly 
his experiments, have been conducted under circumstances un- 
favourable to accuracy of results.” 
So far then was Sir Humphry from being convinced that 
Mr. Ellis was not deceived by his experiments, that he actually 
condemns his experiments as inaccurate. But to prove the error 
of the second statement of W. H. G.; namely, of Sir Humphry’s 
being one of the “ half dozen who experimentally opposed Dr. 
Priestley’s opinion,” we need only refer to the latter part of the 
above page, and also to p. 197. In the first of these Sir H. 
says, ‘In some of the early experiments of Dr. Priestley, before 
he was acquainted with the agency of light upon leaves, air that 
had supported combustion and respiration was found purified by 
the growth of plants, when they were exposed in it for iat 
ays 
