78 Mayow 



Since then the air still remains in these vessels, shall 

 we suppose that it has been condensed and that the 

 ascent of the water results from this ? But neither is 

 this the case, for we note that the water in the glass 

 in which the light has gone out rises above its former 

 level while the air is not yet completely cooled. 

 And indeed the heat caused by the presence of the 

 animal is fitted to produce rarefaction rather than 

 condensation. Besides if the air underwent no other 

 change than condensation only, there is no reason why 

 the lamp or the animal should not have been sustained 

 by it. Should any one happen to say that the elastic 

 force of the air was diminished by the respiration of 

 the animal because some part of the air entered the 

 blood of the animal, I reply that the blood of the 

 animal, when it was enclosed in the glass at first, con- 

 tained an equal and even a larger supply than after- 

 wards of aerial and elastic particles, and it therefore 

 follows that some elastic particles must pass out from 

 the blood of the animal into the glass pari passu with 

 others that enter in, and consequently that elastic 

 particles must be contained in the glasses after the 

 animal has breathed for some time in it in no less 

 abundance than before. Nay, even although more 

 aerial matter should enter the blood of the animal 

 than is given out from it, still it would continue to 

 exist in the glasses, and in accordance with its elastic 

 nature would occupy as much space as otherwise. 



But, to make a conjecture on this difficult subject, let 

 us consider in how many ways the elastic force of 

 bodies may originate. And, in the first place, we 

 notice that the particles of all bodies whatever, when 

 set in motion, open out and seek to expand into a 

 larger volume, inasmuch as they require more space 

 than before for executing their motions. And indeed 



