108 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXVII.) 
below it, not only for different times of the year, but I think in some seasons, even 
at different times of the day. It would require much attention to unravel the whole 
effect. In June, July and August, when the sun and its warm region are greatly 
to the north of the Cape, it appears that the dip is increased as the region passes, 
which would give a rotation of the upper end of the needle like that at Hobarton 
(2909.) ; but in November, December, January, February, March and April, the dip 
diminishes at that time, and the resulting rotation of the pole is of the contrary kind, 
or like that at St. Helena (3057.) and Singapore (3061. 3067.). 
3043. The daily variations of intensity at the Cape are remarkable. In the months 
October to April it is at a chief maximum at 19‘‘ or 20**; by noon it is reduced to a 
minimum as the sun passes over; gradually rises to a second maximum about 4** 
or 5**, and then, after sinking a little about 8^or9'', reaches the chief maximum about 
IS^'or 19'’ next morning. In the months from May to September the chief maximum 
is at 21'’ or 22^ which is followed by a minimum at l'* or 2^, due to the day effect. 
Then comes on the S'* maximum, and after thirteen hours or more the second mini- 
mum as low almost as the former, and only three hours before the chief maximum ; 
so that this maximum is placed between minima close on each side of it. 
3044. These are exactly the months during which the upper end of the needle 
moves eastward in early morning up to 19'’, and that is just the hour when the mini- 
mum intensity occurs. From IS^’or 19'’ to 21'’ the intensity rises to a maximum, 
precisely as the lines of force are moving westward before the sun region, prior to 
their quick return east ; and as they return in their quick journey so the intensity 
falls to a minimum again, and is at that minimum at F or 2'’, just as the swing is 
over. Here is a very close connexion, and it is curious to see the needle end at east 
with minimum power at 18'’, and again also at 1'’, remembering that in that time it 
has swung from east to west and back to east again. 
3045. iSt .Helena*. — This is a station which Colonel Sabtne has distinguished as of 
the highest interest ; being near the line of least force, within the tropics, and with 
little magnetic inclination'!-. It was here also that he called attention to the striking 
fact, that the course of the needle is in some months in one direction, and in other 
months in the contrary for the same hours of the day;};. De la Rive attempted to 
explain this fact§, but Sabine has stated that this explanation is not satisfactory^. 
3046. St. Helena being a small island in the south Atlantic ocean is removed about 
1200 miles from the nearest land. The longitude is 5° 40' west, the latitude 15° 56' 
south ; the mean declination 23° 30' west, and the mean dip 22° south. Hence there 
are three quadrants concerned in the day action of the sun, especially when that 
luminary is south of the equator. The sun is south of St. Helena itself in the months 
* See Tables, pp. 119, 120, and curves of variation, Plate II. 
t Magnetical Observations, St. Helena, 1840 to 1843. J Philosophical Transactions, 1847 , p. 51 . 
(j Annales de Chimie et de Physique, March 1849, tome xxv. p. 310. 
^ Proceedings of the Royal Society, May 10. 1849^?. 821. 
