30 
zontal intensity is a minimum at about 2 and 16 (lunar) hours, 
and a maximum at about 8 and 20 hours. The mean amount 
of the fluctuation is 86 millionths of the intensity, when the 
moon is to the east of the meridian, and 185 millionths, when 
it is to the west. 
The summer and winter lunations yield analogous results. 
These are given in the following Table :— 
TaBrE I].—Diurnal Variation of the Horizontal Intensity related to 
the Moon’s Hour-Angle, in Summer and in Winter. 
Hours. Summer. Winter. 
0 + 8 = 21 
2 — 104 - 1 
4 itn + 27 
6 + 6 + 32 
8 + 96 +119 
10 + UE + 74 
12 + 57 - 6 
“14 + 9 — 22 
16 — 80 — 69 
18 — 39 — 46 
20 + 21 + 4 
22 + 27 — 42 
If it be assumed that the total intensity undergoes no 
change,—or, in other words, that the variation above deduced 
is produced by a change-in the inclination alone,—we can in- 
fer the latter. Its law will of course be similar to that of the 
horizontal intensity, the greatest inclination corresponding to 
the least intensity, and vice versd. The total amount of the 
change, on this supposition, is 0°22, or about one-fourth of 
the corresponding change of the declination. The magnitude 
of the change of direction of the resultant magnetic force in 
the perpendicular plane (= change of declination x cos inclina- 
tion) is 0°27. 
