Fourth Series.— -Conclusion. 



123 



Per-centage of Heat transmitted by several Bodies. 



54>. The leading facts contained in this paper are these : — 

 55. I. The peculiar (red-like) character of films of smoke in 

 transmitting heat of low temperature is partaken, — 



A. By simple powder of charcoal. 



B. By (at least some) other dull earthy powders. 



C. By surfaces simply dull or devoid of polish. 



D. By surfaces irregularly furrowed, as with emery or 

 sand-paper. 



E. By polished surfaces, on which fine distinct lines have 

 been drawn. 



F. By the mechanical lamination of transparent mica, 

 which, as a continuous medium, possesses opposite properties. 



56. II. The following media seem indifferent to the kind 

 of heat which they transmit : — 



A. The thinnest gold-leaf is impervious to any. 



B. Metallic gratings transmit all kinds of heat in a propor- 

 tion which is probably exactly as the area of the interstices 

 which they present. 



C. Thread-gratings. 



D. In a state of powder, most crystalline bodies approach 

 to a condition of opacity for heat. 



57. III. The following bodies, in addition [to those com- 

 monly known, transmit most heat of high temperature {violet- 

 like heat). 



A. Several pure metallic powders. 



B. Rock-salt in powder ; and many other powders. 



C. Animal membrane. 



58. IV. Heat of low temperature is most regularly re- 

 flected at imperfectly polished surfaces. It is also, we have 

 seen, most regularly transmitted. These facts are of great 

 importance to the theory of heat ; and may probably sug- 



