* 
366 M. C. Lea on certain phenomena of Light. 
that it exerted itself in all directions equally while specular re- 
flection took place in the plane of incidence only ; distinguished 
from radiation by the fact that it is not like the latter, preceded : 
by absorption. : 
ifferent substances showed great differences in the energy of 
their diffusion. Smoke black diffused all rays equally, but very 
little. Some diffused largely, and all rays equally; this was 
the case with the metals. Others again diffused rays of high 
refrangibility much more than those of lower refrangibility. 
In seeking analogies between heat and light, Melloni com- 
pared this new function of heat with that species of irregular 
and diffused reflection in light which conveys to our senses | 
the conception of color. Smoke black he observed was truly | 
black as respects heat, as well as light, diffusing in both cases 
very little, but rays of all refrangibilities equally. The metals, 
in their relations to heat, corresponded with bodies white as 
respects light, as they diffused freely, and all rays equally. 
hose bodies which exercised an election to the rays, absorbing 
more of some, and diffusing more of others, he compared to 
bodies which are colored as respects light, This heat color he 
termed thermochrosis. 
the one hand have had only black, white, and blue bodies. re 
on the other hand there should be bodies found absorbing * 
more, and diffusing the less refrangible rays of heat ; these 
pects light, 2 
This defect in the analogy is not alluded to by — 
And of late years this function of heat has been, as Ln ponte 
the quotation already made, compared to one of light disun 
: 2 : 
- for this tendency. Its existence is assum 
a be - oO 
___ but only to be absorbed. Again, he considered the phenome? 
__ which he described to correspond with a set of light-phenomen* 
