Fourth Series. — Laminated and Smoked Surfaces. 73 



be carried upwards indefinitely by interposing screens of differ- 

 ent materials, which either may be proved directly (as I have 

 done in the Third Series of these researches) to increase the 

 refrangibility, or we may take Professor Powell's, or any si- 

 milar test, which our experiments lead us to conclude to be 

 co-ordinate with the fact of refrangibility. Such a prolonga- 

 tion of the scale of heat-sources would be, 



8. Oil-lamp heat transmitted by Common mica. 



9. i Glass (Argand lamp). 



10. Citric acid. 



H. Alum. 



12. Ice. 



A clear appreciation of the scale of refrangibility as the im- 

 portant test for the qualities of heat cannot be too clearly ap- 

 prehended and admitted. Heat from any source, if it admit 

 of transmission at all through glass, alum, or water, will ulti- 

 mately have the character of glass-heat, alum-heat, or water- 

 heat, just as light from the sun, or from a candle, becomes red, 

 blue, or green, by transmission through glasses of these co- 

 lours. 



5. Now, when M. Melloni had shown (and this experi- 

 ment I believe was original to him), that substances which 

 stop every ray of even intense light (as opake glass and some 

 kinds of dark mica), yet transmit a sensible quantity of heat, 

 it was not unnatural to inquire whether the invisible heat thus 

 obtained from a luminous source, might not possess the quali- 

 ties of heat from a dark source, in other words, whether bo- 

 dies, like black glass and mica, instead of stopping the less re- 

 frangible rays like glass, alum, &c, would not suffer these to 

 escape, and absorb the most refrangible rays, acting upon heat 

 as a body does upon light, which stops the yellow, blue, and 

 violet rays, that is, as red glass does. 



6. Experiment partly fulfils this expectation, and partly not. 

 The careful and complete series of experiments made by M. 

 Melloni upon the qualities of the invisible heat thus obtained*, 

 shows, that although it resembles low-temperature-heat, in so 

 far as it is very feebly transmitted by alum or citric acid, yet 

 low-temperature-heat (that from boiling water for instance) 

 is but very faintly transmitted through the black glass or mica, 

 which ought not to be the case if these bodies acted like a 

 sieve, which arrested the more refrangible rays, and suffered 

 the others to escape. 



7. The direct test, however, of examining the refrangibility 

 of the heat rays issuing from opake screens yet remained ; and 



* Annates dc Chimie, Avrtl 1834. 



