PHENOMENA OF THE UNIVERSE. 143 



The mode of the process of water in the expansion and 

 contraction which take place in the body of it through the 

 medium of fire is thus. Water acted upon by moderate 

 heat emits a little and clear vapour, before any other change 

 is seen within the body of it ; the heat then continuing and 

 increasing, the body yet remaining whole, it does not rise 

 nor foam, as it were, in small bubbles, but ascending through 

 greater ones, dissolves itself into copious vapour, but the 

 water soon flies off, and is consumed. And that vapour, if 

 it is not impeded, mingles with the air, being at first visi 

 ble, and even after it has vanished from sight, perceptible, 

 either by sending forth a scent, or by moistening and 

 softening the air at the touch or at breathing. And at 

 length it hides itself, and is lost in that sea of air. But if 

 first a solid body meet it (and so much the more if it be 

 equal to it and polished), the vapour gently enters into it 

 self, and is returned into the water either by the exclusion 

 or ejection of the air, which was before mixed with the va 

 pour. And that whole process is manifest, as well in the 

 decoction of water as in distillation. But we moreover see 

 vapours which are emitted from the earth, if they have not 

 been thoroughly subdued and scattered by the heat of the 

 sun, nor from the coldness of the air equally commingled with 

 that body of air, although they do not meet a solid body, yet 

 returned into water from the very cold and destitution of 

 heat, so that in evening dew it takes place earlier, in showers 

 later. I have, therefore, upon patient and diligent inquiry 

 set down that the expansion of air, if it be compared with 

 water, amounts to a ratio of one hundred and twenty fold 

 or thereabout. 



HISTORY OF THE EXTENSION OF MATTER IN 

 PNEUMATICS. 



I have taken a glass phial which could perhaps hold one 

 ounce ; I made choice of so small a vessel as for two reasons 

 particularly suited to the experiment, first, that it might 

 sooner bring on the boiling with less heat, lest the bladder, 

 which was to be put above the phial, should be burnt and 

 dried up by an intenser heat: secondly, that it might 

 receive a less portion of air in that part which was not to 

 be filled with water : since I was aware that the air itself 

 received extension through fire. I determined, therefore, 

 of making use of but a little air, that that extension might 

 not disturb the ratios of the water. The phial was not 



