[ xlv ] 



that the difficulty of the undertak- 

 ing furpailes their abilities. 



WHEN this book was entirely 

 printed, and nothing but the latter 

 end of the preface unfiniihed, I 

 was informed by my friend the 

 Abbe Fontana, that he difcovered a 

 few days ago a new method of 

 procuring to a lick perfon the be- 

 nefit of breathing any quantity of 

 dephlogiflicated air at a cheap rate. 



This very year a paper of mine 

 was read before the Royal Society, 

 and ordered for the prefs (contain- 

 ing a new theory of the effects of 

 gunpowder, and the difcovery of a 

 new and powerful explofive air), 

 in which I fay, that the rapid pro- 

 grefs our modern philofophers daily 

 3 make 



