14 ANIMALCULA OF INFUSIONS. I, 



altogether prevented, by increafmg the heat. 5^-. 

 condly. Whether the increments of heat prove the 

 diminifhed elaflicity of the air. 



For convenient examination of both, eleven vef- 

 fels, containing eleven kinds of the fame vege- 

 table feeds as before, were hermetically fealed. 

 But, to proceed with due caution, it was effential 

 that the included air fliould undergo no fenfible 

 rarefaction in fealing with the blow pipe, and not 

 lofe its elaflicity, which would alTuredly happen 

 if the veffels were fealed without any further pre- 

 paration, by the flame furrounding and foftening 

 the neck : for fuch powerful heat, after commu- 

 nicating from the neck to the belly, could not 

 but expel great part of the included air, whence 

 the part remaining behind would become more or 

 lefs rarefied, and more or lef? elaflic accordingly. 

 Indeed, when the hermetic feal is broken, after 

 the veffel cools, a faint hifTmg is almofl always 

 heard, which proceeds from the air efcaping by 

 the orifice : and that this is the fact is certain, by. 

 applying the flame of a candle near the feal ; 

 when broke, the flame is driven from the aper- 

 ture, and fometimes actually extinguilhed. If the 

 feal is broken when the veffel is inverted in wa- 

 ter, the water fuddenly rifes above the level of 

 what furrounds the veffel ; a mofl fatisfactory 

 proof of the internal air being more rarefied than ' 

 the external. To avoid this inconvenience, the 



necl\ 



