Proceedings of the British Association.  —-391 
so these other rays were also absorbed, though possibly in a less degree. 
The apparent complementary relation between the color of chlorine 
and that of the ray which seemed to have the highest power, was curi- 
ous, and excited a wish to know if any thing similar occurred in respect 
of the vapor of iodine, or if this power was confined to the blue end of 
the spectrum. 
“ On the Regular Variations of the Direction and Intensity of the 
Earth’s Magnetic Force,’ by Prof. Lloyd. The observations (made at 
the Dublin Magnetical Observatory) were commenced early in the year 
1839, and have been continued, almost without interruption. Since the 
beginning of the year 1840, they have been taken every two hours, day 
and night. The elements directly observed are the declination and the 
two components (horizontal and vertical) of the intensity, and from the 
variations of the latter, those of the total intensity and inclination are 
readily deduced. The variations were projected in curves, which rep- 
resented the course of the mean daily changes for the entire year, for 
the summer and winter half years, and for each month separately. 
Declination.—The mean daily curve of the changes of declination 
for the entire year exhibits a small easterly movement of the north end 
of the magnet during the morning hours, which reaches its maximum 
about 7.a.m. After that hour, the north end moves rapidly westward, 
and reaches its extreme westerly position at 1h. 10m. p.m. It then re- 
turns to the eastward, but less rapidly, the easterly deviation becoming 
a maximum about 10 P.m. The mean daily range =9°3 minutes. Du- 
ring the summer months the morning maximum at 7 a. M. is more mark- 
ed; the evening maximum, on the contrary, disappears, there being a 
slow and regular movement of the north end to the eastward from 7 
P.M. until 7.a.m. In winter, on the other hand, the evening maximum 
is well defined, and the morning maximum disappears, there being a slow 
and regular westerly movement until 9 a.m., after which the move- 
ment becomes more rapid in the same direction. The epoch of the 
extreme westerly position of the magnet is nearly the same throughout 
the year. The greatest daily range, in summer, is about 13°7 minutes ; 
the least range, in winter, about 7°2 minutes. 
Horizontal intensity:—The mean daily course of the horizontal force, 
for the entire year, has two maxima and two minima. The first min- 
imum occurs between 1 a.m. and.8 a.™., which is followed by a max- 
imum about 5 a. M., or a little after. These fluctuations are small. A 
second and principal minimum takes place at 10h. 10m. A. M. 5 and a 
second, or principal maximum, about 6 P.M. The mean daily range 
='0024 of the whole intensity. In the summer months the smaller 
maximum and minimum disappear, the intensity decreasing continually 
throughout the night, but slowly, until 5 or 6 a.m., after which the de- 
crease becomes rapid. There are, consequently, but one maximum 
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