624 
THE EARL OE ROSSE OH THE RADIATION 
details of which have not been preserved. Although the result now given has been 
worked out with every care, it must still be considered simply an attempt to connect 
the readings of the galvanometer with a constant known source of heat ; and we must 
admit that the problem of the determination of the lunar temperature is nearly as far 
removed as ever from our grasp. The formula we have made use of is admitted to be 
a purely empirical one, based on experiments made within very limited ranges of tem- 
perature, within which it appears to agree more closely with the observed law than 
Newton’s more simple formula. Nevertheless we can obviously feel no assurance that 
it is generally true, nor indeed can we employ it, like Newton’s, to determine the excess 
of the temperature of the hotter over that of the cooler body, without knowing one or 
other of the two temperatures. 
I feel that X should not conclude this paper without bearing testimony to the energy 
and perseverance with which my assistant, Dr. Ralph Copeland, lias conducted the 
observations which form the subject of the greater part of it, as also to the great 
care and the ability with which he has worked out the reductions. X had hoped 
to have sent in this paper before the close of last Session ; but the greater completeness 
which is the result of the delay, as well as the fact that the exceptionally unpropitious 
state of the weather would have prevented our profiting, in a new series of observations 
by any suggestions which might have come to us, have removed all cause for regretting 
this. One thing I should have much wished to have added to this investigation had 
there been any reasonable prospect of doing so without considerably more delay — namely, 
a more satisfactory determination of the value of the scale, by means of a comparison of 
the deviations due to solar with those due to lunar radiation, than that given in a former 
communication based on observations made with an uncertain sky and of only two or 
three hours’ duration. 
Appendix. 
Received May 7, 1873. 
Since the foregoing was written an explanation has suggested itself for the very con- 
siderable divergence (more than could fairly be ascribed to errors of observation) of our 
heat-curve from Professor Zollner’s light-curve for change of phase, which will at the 
same time account for the increase of the percentage of heat transmitted by glass towards 
the time of full moon. 
Were it not for the negative result obtained with the thermopile on March 24th, 1871 # , 
the latter fact might perhaps have been attributed to a constant amount of heat emitted 
from the interior of the moon ; but now this explanation is no longer admissible. 
On referring to the Table at page 615 of the foregoing paper, it will be seen that the 
percentage of heat transmitted by glass increases gradually from each side to a maximum 
at or near the time of full moon ; consequently the phase-curve for “ heat through glass ” 
* See page 589, note. 
