VI ADVERTISEMENT. < 
In these additional Inquiries, the Author has 
greatly extended his researches into the " Chan- 
ges induced on the Air by the Vegetation of 
Plants ;" and if his success bear any proportion to 
the pains which he has taken, he hopes that he may 
be found to have disentangled some of the perplexi- 
ties, and reconciled some of the differences which 
have hitherto prevailed on this important subject. 
The views which he has suggested respecting the 
" Colours of Plants" arose naturally in the order 
in which they are presented ; and the attempt to 
connect them with other curious operations in the 
vegetable economy, will, he trusts, add consider- 
ably to their interest and value. If an apology be 
deemed necessary for the length to which he has 
extended the section on the " Agency of Light," 
he would beg to state, that some parts of that 
section were composed with reference to ulterior 
views, which, for the present, he has been induced 
to postpone. 
On the second branch of his Inquiries, namely^ 
that which relates to " Animal Respiration," the 
Author has diligently sought information from all 
the sources which lay open to him ; and the im- 
portant additions, which the labours of his Con- 
temporaries have enabled him to make to this part 
of his Work, will, he trusts, be considered not only 
as valuable in themselves, but as tending to aug- 
ment the confidence of his readers in the conclu- 
sions to which he had before endeavoured to con- 
duct them. To the chapter on the " Source 
