£2 ESSAYS AND OBSERVATIONS 



cret operations of Nature is not to be exped:^ 

 cd J for they certainly depend, in great 

 meafure, upon laws and principles utterly un- 

 known to us. 



13. Ir one beam or ray of light, by paf- 

 fing ftraight onwards thro' the fame pellucid 

 fubftance, can communicate no heat to its 

 internal parts ; neither will the greateft 

 quantity of rays, tho' crowded into the nar- 

 rowefl fpace, by croffing one another. From 

 hence it follows, that the portion of air 

 which lies in the focus^ of the moft potent 

 fpcadum is not at all affeded by the paflage 

 of light thro' it, but continues of the fame 

 temperature with the ambient air ; altho' 

 any opaque body, or even any tranfparent 

 body denfer than air, when put in the fame 

 place, would be intenfely heated in an in- 

 ilant. 



14. This confequence, evidently flowing 

 from the plainefl and moft certain principles, 

 feems not to have been rightly underftood 

 by many philofophers '^ : for which reafon, 



I 



* See Boerhaave tievatnt. chetn. torn. i. on lire, coroll. 

 5. after exper. 14. and coroll. i, and 7. after exper. 17. 

 See alio Rutherforth'i fyflem of natural phildfophy, prop. 



556. 



