



I 



V The P R E F A C E. 



li'herc it appears by many chymio ft at teat 

 Experiments, that there is diffused thro' all 

 natural, mutually attracting bodies, a large 

 proportion of particles, which, as the fir ft great 

 Author of this important difcovery, Sir Ifaac 

 Newton o'ferves, are capable of being thrown 

 off from denfe bodies by heat or fermentation 

 into a vigoroufly elaftick and permanently re- 

 pelling ft ate : And alfo of returning by fer- 

 mentation and fometimes without it, into 

 dtnfe bodies ; It is by this amphibious pro- 

 perty of the air, that the main and principal 

 operations of Nature are carried on ; for a 

 tnafs of mutually attracting particles, 'with- 

 out being blended with a due proportion oj 

 elaftick repelling one should in many cafes foon 

 coa'efce into aJluggiJJj lump. It is by thefe pro- 

 perties of the particles of matter that hefolves 

 the principal Phenomena of Nature. AndT)r. 

 Frcind has from the fame principles given a 

 very ingenious Rationale of the chief opera- 

 tions in U .miftry. It is therefore of impor- 

 tance to have thefe very operative properties of 

 natural bodies further afcertained by more 

 Ex ft rimcnts and Obfervations : And it is 

 with fat if action that we fee them more and 

 more confirmed to us, by every farther enquiry 







