On Sal Nitrum and Nitro- Aerial Spirit 71 



it rests be removed from the sun's rays, that the air 

 enclosed in it may cool again and return to its former 

 condition, and then you will find that the water within 

 has risen above the point marked at first. And indeed 

 I have found by calculation that the air has been 

 reduced in volume by about one-thirtieth by the burn- 

 ing of the light. 



After the smoke of the burning light with which the 

 cupping-glass was filled had entirely disappeared and 

 the glass had become as bright within as at first, I tried 

 to kindle the light in it a second time by throwing the 

 solar rays upon another piece of camphor, suspended in 

 the glass in the same way as before, but the experiment 

 did not succeed — a sufficiently clear proof that the air 

 had been, by the burning of the light, deprived of its 

 igneo-aerial particles, so as to be quite unfit for sustain- 

 ing flame anew. But lest any one should think that the 

 light could not be kindled a second time in the glass, 

 because the inner sides of the glass had been dimmed 

 so much by the smoke of the light previously burned 

 in it that the rays of light could not be transmitted 

 through the glass with sufficient intensity, I fasten a 

 piece of paper about a hand-breadth broad, with its 

 margins all round coated with the aforesaid paste, to 

 the inner side of the cupping-glass at the place where 

 the solar rays are to be transmitted. When the fumes 

 have entirely vanished this paper is to be pulled off, 

 by a thread attached to it and extending outside the 

 vessel, so that the solar rays may pass through the part 

 of the glass which has been protected from the soot. 



It is a further confirmation of our hypothesis that 

 the air given out from the lungs of animals has its 

 elastic force diminished in consequence of the loss of 

 its nitro-aerial particles, as will be manifest from the 

 followinsf. 



