KNOBLAUCH ON RADIANT HEAT. 425 



rays present in so many respects, and especially in their deport- 

 ment after diffuse reflexion itself. 



MeUoni* has expressed the view, that yellow rays appear the 

 most intense to us because the retina of the eye is yellow. Now 

 if this yellowness, supposing that it does occur in a living, healthy 

 eye, which is denied by most German physiologists, does not 

 arise from a peculiar excitation of the retina, by means of which 

 it emits yellow rays, but, in correspondence with the previous con- 

 sideration, merely in consequence of its reflecting them, should 

 it even then be assumed that our retina receives a special ener- 

 getic impression from yellow rays? Certainly not; for the 

 experiments on the absorption of heat have taught us that a 

 body is least affected by those rays which its suiface reflects. 

 (See particularly p. 421.) 



VI. On the Sources of Heat. 



In the previous section it was shown that rays of heat under- 

 going diffuse reflexion by different bodies do not experience any 

 peculiar change, but merely selective absorption, by means of 

 which certain rays are checked, others reflected unchanged. (See 

 p. 415-422.) 



Hence it follows, that when e. g. the rays of an Argand lamp 

 reflected by carmine exhibit a different deportment (on trans- 

 mission through diathermanous substances) to those reflected by 

 black paper (see p. 402-404, and 406, 407), this can only arise from 

 these sources of heat containing different rays, some of which 

 are reflectible by carmine, others by black paper. The greater 

 the difi'erences are which occur after reflexion by various bodies, 

 so much the more heterogeneous must the number of rays be 

 which are emitted by the original source of heat. 



Now if we find that the differences which the heat of the red- 

 hot platinum exhibits after reflexion from a certain number of 

 different bodies (on transmission thi'ough diathermanous media) 

 are all less than the heat of the Argand lamp reflected by the 

 same surfaces examined in the same way evinces (see p. 403-405), 

 we must conclude that the red-hot platinum emits rays of heat 

 which are less heterogeneous than the latter. 



Moreover, if we remark that the differences in the rays of 

 heat o{i\\e flame of alcohol, when reflected by various bodies (as 

 they appear on using the same diathermanous bodies), arc all 

 • E. Secbcck also adopts this view. 



