330 Baeppicker— On the Changes of the Radiation of Heat from the Moon. 
On Nov. 14, 1872, clouds interfered much ; but from simultaneous determina- 
tions of the heat and light at intervals when the sky was fairly clear, it appeared 
that during this partial eclipse the decline and subsequent increase of heat, as 
measured by the thermopile, took place about as rapidly as that of the light as 
measured by Zéllner’s photometer. 
On Aug. 23, 1877, some determinations of the heat during the /o¢al eclipse 
were made. Clouds again interfered, and the observations were very unsatis- 
factory, but after considerable delay were published in Copernicus, vol. i. p. 22. 
No further opportunity for prosecuting the inquiry occurred until last October, 
when the above measurements were made under exceptionally favourable condi- 
tions in the opinion of Dr. Boeddicker (I was myself absent in America at the 
time). From theoretical considerations it seems difficult to reconcile the rapid fall 
from, probably, 359 divisions before the eclipse down to 4 only during totality, 
with so large a defect as 48 divisions (or 13 per cent.) after an interval as long as 38 
minutes since the end of the eclipse. But as all attempts to find an explanation, 
where it might be natural to look for it, in the condition of the apparatus and 
the method of observation, have failed to afford a clue, it seems best to give the 
investigation to the world without further delay, reserving comment for a future 
time. 
A total eclipse, where a sufficient altitude during the whole of its duration is 
attained, and where our climate allows of the phenomenon being taken advantage 
of, is so rare, that it may be some years before an opportunity for repeating the 
investigation may occur. 
A sufficient explanation of the change of percentage of heat transmitted by 
glass with the change of phase still remains to be found. That suggested in 
Phil. Trans. 1873, pp. 626, 627, is probably quite inadequate ; and the assumption 
that it is due to a constant elevation of temperature, independent of that due 
immediately to the sun’s action, would be quite inconsistent with the very rapid 
fall of temperature to about ,!, of the full moon value in the short duration of the 
total eclipse, also with the fact that the observed heat falls away to an almost 
imperceptible amount even at some distance from conjunction PAil. Trans., 1878, 
p- 604). 
Birr Caste, April 17, 1885. 
