THEORY OF LIGHT. 49 



matter of glass diminishes its power of transmitting heat, yet 

 that red, orange, yellow, blue, violet, and white glass, trans- 

 mit calorific rays of all degrees of refrangibility ; but that 

 green glass, on the contrary, possesses the peculiar property of 

 transmitting the least refrangible calorific rays, and of stopping 

 the most refrangible. 



The same elective action is exercised by green colored glass 

 on heat, as that of red glass on light. 



The sulphates of alumina and lime produce the opposite 

 effects to those of green glass on heat, by transmitting the 

 most refrangible rays with the greatest facility. 



It is worthy of observation, that heat which has been trans- 

 mitted through green or opaque black glass, will not pass 

 through alum, although that which has traversed glass of other 

 colors is transmitted most readily ; neither will the heat which 

 has passed through alum find its way through opaque sub- 

 stances, while abundantly transmitted through transparent and 

 colorless bodies : and this would infer that the properties of 

 heat emanating from alum nearly approach those of light and 

 solar heat. 



From a review of the various experiments on heat by Sir 

 Win. Herschel, Dr. Wollaston, MM. Ritter, Buckman, and 

 De Laroche ; professors Powell and Forbes ; Mr. Lloyd, 

 M. Melloni, as well as of those preceding philosophers, MM. 

 Malus, Berard, Leslie, &c. ; most of the inferences occur- 

 ring, they correspond in exhibiting the strong analogy that exists 

 between the properties of heat and light, and I beg to refer the 

 reader to that exquisite work, Mrs. Somerville's " Connection 

 of the Physical Sciences," which stands unequalled among the 

 contributions of modern writers, as to variety of subjects and 

 the admirable talent and grace with which they are discussed. 



Now from the prolongation, the radiation, reflection, and 

 other properties of heat, exactly consonant to those exercised by 

 light from the power of some media, solid and fluid, to pro - 

 duce a change in the nature of heat, as to its easy or difficult 



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