385 
age. The diurnal range is the phenomenon in which the so- 
lar magnetic action is most conspicuously displayed ; and in it, 
if anywhere, we should expect to find evidences of the periodi- 
cal action of another luminary. In fact, ifthe moon co-operates 
with the sun, in the course of the day, in its effect upon the 
position of the free magnet, we should expect the range to be 
greater in certain portions of the moon’s age than in others, 
the separate actions of the two luminaries, as in the analogous 
case of the tides, at one time conspiring, and at another being 
opposed. We have, therefore, only to analyze the diurnal 
range, in reference to the moon’s age, and such joint action, 
if it exists, will be manifested by a variation in the magnitude 
of the range, whose period is the synodic month. 
‘J have, accordingly, calculated the daily range of the de- 
clination for eleven years, viz., from 1840 to 1850 inclusive, 
and arranged the resulting numbers according to the moon’s 
age. As there are two periods of greatest easterly deviation 
of the magnet in each day, the range is double, viz., from 
7 a.m. tol p.m., and from 1 p.m. to 10 p.m.; the mean of 
these is here taken. When the twelve lunations of each year 
are combined, and the means of the ranges corresponding to 
_the same day of the moon’s age taken, the resulting numbers 
exhibit a periodical variation, the range being greatest in the 
first and third quarters, and least in the second and fourth. 
_ But as the law is not exhibited with distinctness for each year, 
_ eyen in these numbers which are the means of 24 separate 
_ results, I have again combined them in groups of 7 and 8 al- 
following Table gives the results. The numbers are the dif- 
_ ferences between the mean ranges in each of the four quarters 
and in the entire month, for each of the eleven years :— 
: ternately, corresponding to the four quarterly periods. The 
; 
4 
a) ph be a i i 1 ee, i a a i dk i li i, i A 
