608 
THE EARL OP ROSSE OH THE RADIATION 
The corrections for the changes of the moon’s phase and semidiameter during the 
observations were very small, on which account the particulars are omitted, as also the 
adopted mean elongation, semidiameter, and sidereal time, which are the same as for 
the total heat determinations. The observations are satisfactorily represented in altitude 
by the Table already deduced. Although these results were fully examined by means 
of a curve like that for the total heat, it is not necessary to give further particulars here, 
as these observations will afterwards be combined with others, of which we must now 
give an account. 
Observations made during the Autumn of 1870. 
The preceding investigations having thus given, at least, a tolerably close approximation 
to the law of the extinction of the moon’s radiant heat in our atmosphere, and the extent 
to which its amount is influenced by her change of phase, we are in a position to make 
use of a compact series of observations made in the autumn of 1870. These are, as a 
rule, confined to low altitudes ; and the range on any given night is, with one or two 
exceptions, so small that they could not have been used with advantage in the con- 
struction of the altitude curve, nor, owing to alterations in the height of the directive 
magnet of the galvanometer, were they at once available for the determination of, or 
comparison with, the phase curve. However, as they were made for the most part under 
■very favourable circumstances of weather, and as from their chiefly referring to the 
waning moon they are important as filling an all but vacant gap in the records of 
1871-72, they are introduced here, although out of their chronological order. The 
particulars of the observations are arranged in nearly the same way as those already 
discussed, the only difference being that the sets taken with a plate of glass interposed 
are left in their original place in the journal. As a matter of convenience, and on 
account of its greater accordance with fact, the Phase Table at p. 605 was used in place 
of Lambert’s formula for the correction for the change of phase. The Table of $z was 
used for reducing to the zenith. In this way the quantities in column “ log (G corr.) ” 
were obtained. 
Occasionally the time of observation was not noted, but it could generally be deter- 
mined with sufficient accuracy from the measured altitudes of the moon. As has been 
already mentioned, some uncertainty exists as to the height at which the directive 
magnet was placed on some nights ; but as it was always used in one or other of two 
positions (3-00 or 3-46 inches), the directive force on the needle being as little as 0-6579 
in one position as compared with unity in the other, little anxiety can arise as to the 
correctness of the assumptions made. 
The following Tables contain the Journal of Observations and their reductions, which 
will be readily understood on comparison with those already given. 
