626 
THE EAEL OE EOSSE OH THE EADIATION 
Sir John Herschel. 
s. 
Moon’s light. 
S. 
Moon’s light. 
o 
-75 
81-6 
o 
-13 
269-6 
-59 
127-0 
- 1 
417-3 
-51 
112-9 
+ 13 
300-4 
-48 
144-6 
+ 28 
244-6 
-46 
134-4 
+41 
171-7 
-39 
151-1 
+44 
166-2 
-37 
165-3 
+ 82 
52-4 
-19 
243-0 
Then tracing with a perfectly unbiassed mind the curve given in Plate XLVIXL 
(Curve D), and not until afterwards superposing the curve of “ heat through glass,” treated 
as already stated, there was found to be a fair agreement between the two curves. 
For the luminous rays, then, from the moon, the results obtained with the eye aided 
by the photometer and those derived from the indications of the thermopile are as 
nearly identical as could be expected; and it seems just to seek for the explanation of 
the far greater divergence (see Plate XLVIII., Curve C), under more favourable circum- 
stances of observation, of the “ total heat-curve ” in a real difference between the laws 
which govern the emission of heat and light from the lunar surface. 
Let us for the moment assume with Zollner that the moon’s surface is covered with 
angular ridges, whose sides are planes of, say, 52 e inclination, and whose direction is 
perpendicular to the plane in which the earth, sun, and moon lie. The sun’s light will 
then in many parts shine on one side only of each of these ridges, which will reflect or 
diffuse the incident light diminished by the amount absorbed. Let 1—[Jj — quantity 
absorbed, ^ = that emitted. 
Some of the latter will strike the shaded sides of the ridges, but of this 1 — ^ will be 
absorbed and only p emitted. With the heat, however, this will not be the case. If the 
moon’s temperature be assumed from moment to moment practically constant, the whole 
of the heat which falls on her surface must necessarily leave it again ; whereas for every 
unit of light and heat which falls on the surface, of the former only p leaves it after one 
reflection, + after two reflections, fx ? after three reflections, and so on. Therefore the 
proportion of heat emitted by the shadows will be, as compared with the light coming 
from those same parts, ^ times greater than what comes from the parts in direct sun- 
light; the heat emitted in directions removed some distance from the sun will be larger 
compared with that thrown back more towards the sun, and the greater flatness of the 
heat-curve and the increase of percentage of heat transmitted by glass at or near full moon 
are at once explained. 
The complete solution of the question would probably be complicated, and, owing to 
the very unequal distribution of mountain and plain, perhaps unprofitable, even if we 
possessed fuller data than we at present have on which to base our calculations. 
