HEAT OR CALORIC. 37 



(I.) There is heat in every thing, even in ice itself ; and there is 

 no reason to believe that we have ever attained the maximum of 

 cold. 



6. THERE ARE RAYS OF HEAT, DISTINCT -FROM LIGHT. 



(a.) They obviously pass from all hot or warm bodies, whether lu- 

 minous or not. 



(b.) They flow from nearly all luminous bodies. 



(c.) From living animals. 



(d.) From hot water, and other hot fluids, excluding those that 

 require ignition to sustain their fluidity. 



(e.) From a hot ball of iron which is not luminous ; from a hot 

 stone, a hot brick, or other heated incombustible body.* 



(f.) From a close stove supposing no chinks for the light to 

 pass, and, 



(g.) Probably from all bodies whatever, and at all temperatures, 

 there is a certain amount of radiation of heat, although die colder 

 the body is, the less the radiation will be. 



7. RAYS OF CALORIC ARE EMITTED FROM THE SUN, and they 

 are capable of being separated from those of light. 



(a.) Dr. Herschel, using the telescope to look at the sun, em- 

 ployed colored glasses to diminish the light; when their color was 

 deep enough to screen the eyes, the glasses became hot and crack- 

 ed ; in some cases there was very little light, while the heat was painful 

 to the eye, and some glasses transmitted much light but very little heat. 

 He therefore examined the heating power of the different rays, sep- 

 arating them by a prism, and permitting the different colored rays in 

 the well known order of red, orange, yellow, green, blue, indigo, 

 violet, to fall on a delicate thermometer two other thermometers 

 being placed near, as standards ; the thermometer which indicated 

 the heat, lay upon an inclined table. 



(b.) The heat was greatest in the red, or least refrangible rays ; 

 and it was least in the violet, or most refrangible. If when in the 

 violet it was as 16 in the green, it was as 22.4, and in the red, 55. 



(c.) The greatest illuminating power ivas in the middle of the 

 spectrum, and it diminished either way. 



(d). When the thermometer was carried beyond the red ray, and in 

 the same line, the fluid still continued to rise ; the maximum effect was 

 half an inch beyond the red, fyc. ; one inch beyond, the same as in 

 the middle of the red ray ; the heating power was sensible at one 

 and a half inch beyond the red ray. 



(e.) The focus of heat is probably not less than one fourth of an 

 inch farther from the lens than the focus of light. f 



* They are supposed to be hot, in order that the radiation may be evident : the 

 radiation would exist, although in a less degree, if the bodies were cold. 

 t Phil. Trans. 1800, pp. 2589. 



