66 ©f t$e ^ettymcal ©tfgtne 



may be produced in cold bodies by 

 Percuffion^ or Collifion 5 the later of 

 which feems but mutual Percuffion. 



But Inftances of the fame fort 

 with the reft mention'd in this VI. 

 Experiment being obvious enough, 

 I (hall forbear to multiply and infift 

 on them« 



EX PER. IX. 



FOr the fake of thofe that think 

 the Attrition of contiguous 

 air is ncceflary to the Producti- 

 on of manifeft Heat , I thought a- 

 mong other things of the follow- 

 ing Experiment, and made Trial of 

 it. 



We took fome hard black Pitch, 

 and having in a Bafon, Poringer ? or 

 fome fuch Veflel ^ placed it a conve- 

 nient diftance under water, wecaft 

 on it with a good Burning-glafi the 

 Sun-beams in fuch a manner ^ that 

 notwithftanding the Refraftion that 

 they fufferd in the paflage through 



the 



