OF HEAT FROM THE MOON. 
595 
of G corrected for change of phase, change of distance, and for the variation of the values 
of the scale. 
These corrected values of log G are now available for the determination of the law 
of the extinction of the moon’s radiant heat in the earth’s atmosphere. For this 
purpose a graphic method, suggested by that employed by Seidel* in his researches 
concerning the extinction of stellar light, was made use of. The night’s observations were 
arranged in order of zenith-distance, then from the log (G corr.) corresponding to the least 
zenith-distance on any given night each other log (G corr.) of that night was subtracted. 
The logarithmic differences so obtained were then entered on a sheet of cross-lined paper 
as ordinates, the zenith-distances being taken as abscissae ; a curve drawn through these 
points gave what might be called the reducing curve in zenith-distance for that night. 
A second night’s observations were then treated in the same way, and the resulting curve 
moved up or down until it intersected the first night’s curve at the middle of their 
overlapping parts. A third curve corresponding to a third night was then drawn and 
made to agree as nearly as possible with the mean of the curves already laid down ; in this 
way thirty-three curves representing the logarithmic differences of the moon’s radiant 
heat at different zenith-distances were laid down. 
The mean of the differences in each degree of zenith-distance was now entered as a 
point at its corresponding mean zenith-distance on a separate sheet of paper, the number 
of observations being indicated by short radiating lines, in the way often adopted for star 
magnitudes, a simple dot representing a single observation. The ordinates of a curve 
drawn through or near these points gave a provisional Table for <pz, or the logarithm that 
must be added to that of the reading at any zenith-distance to obtain the logarithm of 
the reading as it would have been shown had the moon been in the zenith. The Table 
thus deduced for the extinction of the moon’s heat is here given in an abbreviated form. 
Zen.-dist. 
4--. 
O 
29 
0-0070 
30 
0-0071 
35 
0-0089 
40 
0-0124 
45 
0-0189 
50 
0-0296 
55 
0-0447 
60 
0-0665 
65 
0-1025 
70 
0-1525 
75 
0-2200 
79 
0-3079 
* ‘ Enter suchungen iiber die gegenseitige Helligkeit der Eixsterne erster Gr5sse nnd iiber die Extinction des 
Licktes in der Atmospkare. Nebst einem Anhange iiber die Helligkeit der Sonne verglichen mit Sternen, und 
iiber die Licbt reflectirende Eraft der Tlaneten.’ Yon Ludwig Seidel. Munich, 1852. 
4 L 
MDCCCLXXIIT. 
