122 Dr. Percival on the different ^lantities 



ussSSSEK3»» 



On the DIFFERENT QUANTITIES of Rain whtch 

 FALL, at different Heights, over the fame 

 Si»OT /t/" Ground, with a Letter /rowz Benja* 

 MiN Franklin, LL. D. By Thomas Per- 

 cival, M. D. ^c. Re^,d January 21, 1784, 



T T is a refledion which may mortify pride 

 and humble arrogance, but ought certainly 

 to animate the fpirit of patient attention, and 

 confole us under the difappointments of philo- 

 fophical purfuits, that many of the mod interefl;- 

 ing laws of nature have remained undifcovered, 

 till fome happy coincidence of circumftances 

 hath pointed them out to inquiry or obfervation. 

 Thus the energy of fire muft have been known 

 and felt from the creation of the world ; but 

 the regularity of the expanfile power, on dif- 

 ferent bodies, is a modern difcovery, of un- 

 certain date. And the real nature of this fubtile 

 element, which pervades and aiftuates all matter, 

 and is continually perceptible to our fenfes, is 

 yet but imperfectly explored. The ancients 

 were acquainted with the magnifying power 

 of denfe mediums; and Seneca has noticed, that 

 fmall letters appear larger and brighter when 

 viewed through a glafs globe filled with water. 

 He has remarked, alfo, that apples are more 



beautjfulj 



