345 
and charcoal, are developed from water by the organic 
powers of plants, assisted by solar light *. 
650. The discoveries of Mr Davy, however, which 
are scarcely more to be valued for the actual addi- 
tions they have made to the sum of our knowledge, 
than for the corrections they have introduced into 
what we were before supposed to know, have dis- 
closed new sources of fallacy in these experiments, 
which the state of science, at the period they were 
made, could not have enabled their authors to foresee. 
" The experiments," says he, " in which it is said that 
alkalies, metallic oxides, and earths may be formed 
from air and water alone, in processes of vegetation, 
have been always made in an inconclusive manner ; 
for distilled water may contain both saline and me- 
tallic impregnations ; and the free atmosphere almost 
constantly holds in mechanical suspension solid sub- 
stances of various kinds." " The conclusions of 
M. Braconnot," he adds, " are rendered of little avail 
in consequence of these circumstances. In the only 
case of vegetation in which the free atmosphere, in his 
experiments, was excluded, the seeds grew in white 
sand, which is stated to have been purified by wash- 
ing in muriatic acid ; but such a process was insuffi- 
cient to deprive it of substances which might afford 
carbon or various inflammable matters." 
651. " In the common processes of nature," con- 
tinues Mr Davy, " all the products of living beings 
may be easily conceived to be elicited from known 
combinations of matter. The compounds of iron, of 
Nicholson's Journal, vol. xviii. p. 27- 
