43 
SECT. IX. 
IV. THE COMPOSITION OF WATER. 
Nymphs! let your squadrons watch with chemic eyes 
The fine elastic vapours, as they rise; 
With playful force arrest them as they pass, 
And to pure air* betroth th e flaming gns.f 
Darwin. 
Previous to our entering upon the subject of the effects of air on the 
vegetable oeconomy, it will be necessary to shew, also, that water, though it 
be the solvent of a vast variety of bodies, is neither that compound or Ample 
element formerly supposed, but made up of two very distinct and different 
principled. 
The new and beautiful doctrine of the French chemist, respecting the 
composition of air, was daily gaining ground, and obtaining the applause of 
every one, when an experiment performed by Dr. Priestley made it for a 
while totter on its basis. 
In the middle of a long glass tube this great experimentalist put some 
calcined lead, and affixed to the extremities bladders which were filled with 
inflammable air.% Having applied a strong heat to the middle of this tube, 
* Oxgen air. 
f Inflammable air , very improperly denominated so; for, the burning of all bodies is nothing more, 
as we saw in the last section, than the decomposition of oxygen air. It is the oxygen air, there¬ 
fore, and not the combustible body, that gives out light and heat. When we are sailing on the water 
in a still day, distinct objects appear to meet us, but our reason corrects the delusion. When we 
behold the sun, moving from east to west, philosophy again assumes its empire, and we are convinced 
it is stationary'. If we take a prism, it displays to us a variety of colours; our reason tells us here 
also, that theje colours arise from the rays of light, and are not in the prism, — so of the combustion 
of bodies, the caloric and light are not from the wax of our candles, but from the oxygen air, which, 
as we see in many experiments, becomes, under certain circumstances, decomposed. Vide note (*), 
page (4l). 
+ This air Dr. Prieftley obtained from diluted vitriolic acid poured on iron. Iron was therefore 
said to contain a great quantity of this air. But the fact will soon appear that the air arose from the 
decomposition of water mixed with the vitriolic acid. 
