EARTH’S MAGNETISM TO THE SOLAR AND LUNAR PERIODS. 109 
it was made, of above twenty scale division (twelve times the resulting range of 
horizontal force in the lunar hour angle curve), was rejected, and an interpolated 
quantity substituted ; this elimination, however, was not found to affect the pe- 
riods of maxima and minima; it reduced the range, and rendered the curve 
somewhat more regular. In the observations for 1845, as a farther check on these 
eliminations, a different test number was employed, namely, forty scale divisions, 
or nearly twenty-five times the resulting range of the lunar hour angle curve. 
24. In both years, he minimum occurs at 20%, or 5 before the meridian 
passage; tie maximum at 14", or about 13" after the inferior passage: in both 
years, @ minimum occurs at 8"; in 1844, @ maximum occurs before 4"; and in 
1845, before 3". The maximum at 3°, for 1845, differs little from the maximum 
at 14"; but the maximum at 4", in 1844, is considerably less than the maximum 
at 14". The coincidences of these results may be considered extraordinary, when 
it is known that the range in 1844 is only 0:000211, and in 1845 only 0-000213, 
or less than the effect of one degree of Fahrenheit on the magnetism of the bifilar 
bar. 
25. Several questions spring from this result of the connexion of the intensity 
with the moon’s hour angle. Does the range of the lunar hour angle curve vary with 
the moon’s declination? If so, then we do not eliminate the lunar effect from 
the solar day curve by a monthly or any other summation. Do the periods 
of maxima and minima vary throughout the lunar month in the lunar hour angle 
curve, as they do through the year in the solar day curve? These questions 
I shall endeavour to examine at another opportunity. 
MAxkERSTOUN, December 26, 1845, 
