Bappicker—On the Changes of the Radiation of Heat from the Moon. 329 
c. The minimum of the heat-effect falls decidedly later than the minimum of 
illumination, which may be supposed to coincide with the middle of the eclipse. 
This is obvious, as the values observed before the total phase are larger than 
those recorded at equal times after it. 
These results are so much more remarkable, as they are opposed to the result 
of the eclipse observations of Noy. 14, 1872, which was, however, only obtained 
through clouds (/. ¢., p. 619), and as my extra eclipse observations seem to confirm 
the fact found out in 1878, that the maximum of lunar radiant heat takes place 
before full moon (J. ¢., p. 606), 
NOTE BY THE EARL OF ROSSH, LL.D., F.RS., &e. 
In communicating the above to the Royal Dublin Society it may be as well to 
state shortly with what object the observations during the eclipse were under- 
taken, and to what point the investigation has been brought. 
Having satisfied myself by the series of measurements of the Moon’s Radiant 
Heat, published in the Proc. Roy. Society, 1869, No. 112, p. 487, that it was not 
only possible to perceive it by means of the thermopile, but even to determine 
its amount with tolerable accuracy ; also by the series given in the Proc, Roy. 
Society, 1870, No. 123, p- 9, that, while from its varying largely with the phase of 
the moon, the heat had its origin rather from the sun than from the interior of 
the moon, and that from the much smaller percentage of it transmitted through a 
sheet of glass than of the sun’s direct heat, it was in a large measure absorbed and 
then radiated, rather than instantaneously reflected or diffused, it became of interest 
not only to undertake a more careful and extended series of measurements and 
fully reduce the results, but also to try to obtain a little more information on the 
rate of heating and cooling of the moon’s surface under the changing amount of 
the sun’s rays. Accordingly the investigation published in the Phil. Trans, of 
1873 was undertaken. So far from there being, as might have been expected, a 
greater lunar temperature after full moon than at a corresponding distance before 
opposition, if anything, the reverse appeared to be the case, perhaps from differ- 
ence of average physical conditions between the two (preceding and following) 
visible portions of the surface. It then occurred that it would be important to 
seize the opportunity afforded by an eclipse of measuring the heat under changes 
of illumination far more rapid than those due to phase. 
On May 22, 1872, clouds entirely prevented observations during the whole 
duration of the partial eclipse. 
TRANS. ROY. DUB. SOC., N.S. VOL. III. 2X 
