334 APPENDIX. 



non-conductors of Heat ; or that all interchange 

 and communication of Heat among their particles, 

 as from one of them to the other, is absolutely 

 impossible. Glass, when rendered of a loose tex- 

 ture, conducts Heat with very great difficulty j 

 insomuch that the lava of a volcano has, sixteen 

 years after an eruption, been found red hat a foot 

 under the surface of such glass, though this was 

 quite cool. This circumstance might very pro- 

 bably give the hint for the assertion (paradoxical 

 as it may seem without proper deliberation) that it, 

 would be no difficult matter to convey an iron ball 

 red hot from London to Lincoln: to perform this, 

 it must be inclosed in pumice stone, which is very 

 porous glass, formed by volcanos, and then co- 

 vered over with fur, It is also easy, by covering 

 a room with (he to preserve the air in it of the 



same 



14 of it, one would imagine it would require no great effort of 

 " genius to discover that it would be equally efficacious for 

 " preventing the Heat without from coming in. But natural 

 " as this conclusion may appear, I believe it has never yet 

 " occurred to any body ; at least I am quite certain that I 

 " have never seen a double window, either in Italy, or in any 

 " other hot country, I have had occasion to visit." 

 A little farther on, he says, " There is no communication 

 of Heat between one particle of air and anotiter particle of air* 

 From hence it follows, that though air may, and undoubt- 

 edly does, curry off Heat, and transport it from one place, or 

 from one body to another, yet a mass of air in a quiescent 

 state, or with all its particles at rest, could it remain in that 

 state, would be totally impervious to Heat; or such a mass 

 (l of air would be a perfect non-conductor," 



Much curious and valuable information on this subject may 

 be found in Professor LESLIE'S Experimental Inquiry init (lie 

 Naiun and Propagation qf Heat, lately published. 



