• 2 ; 8 Mr. l\\ u II G A N ' s Experiments, Sec, 



'<\nd was for fome time difpofed to believe the contrary of what 

 I am now convinced to be the truth. Indeed, if we reafon 

 fi priori, I think we cannot luppofe a perfect vacuum to be a 

 perfect condudor without fuppofing an abfurdity: for if this 

 were the caie, either our atmofphere mufl: have long ago been 

 deprived of all its ele6tric fluid by being every where lur- 

 3'ounded by a boundlefs conductor, or this fluid mufl: pervade 

 every part of infinite fpace, and confequently there can be no 

 Ihch thing as a perfe6l vacuum in the univerfe. If, on the 

 contrary, the truth of the preceding experiments be admitted, 

 it will follow, that the conducting power of our atmofphere in- 

 creafes only to a certain height, beyond which this power be- 

 gins to diminifli, till at lafl: it entirely vaniflies ; but in what 

 part of the upper regions of the air thefe limits are placed, I 

 will not prefume to determine. It would not, perhaps, have 

 been difficult to have applied the refults of fome of thefe ex- 

 periments to the explr.nation of meteors, which are probably 

 owing to an accumulation of eledtricity. It is not, however, 

 my prefent defign to give loofe to my imagination. I am fen- 

 fible, that by indulging it too freely, much harm is done to 

 real knowledge ; and therefore, that one fa£t in philofophy well 

 afcertained is more to be valued than whole volumes of fpecu- 

 lative hypothefes. 



Chatham-Place, Feb. 12, 1785. 





y 



