THE MAGNETIC DECLINATION AT ST. HELENA. 
57 
one hand, and Hobarton and those months at St. Helena which form the southern 
summer, is not preserved in the night portion of the curve. 
If the phenomena of the diurnal variation at St. Helena are characteristic of 
a station situated between the northern and southern magnetic hemispheres, par- 
taking, although in opposite seasons, of those contrary features which separately 
prevail in the two hemispheres throughout the year, then we must regard the diurnal 
variation at the Cape of Good Hope, notwithstanding the remoteness of the situation 
of the Cape from the terrestrial equator and from the line of no dip, as supplying an 
additional illustration of the phenomena of an intermediate station. The projections 
in fig. 5, corresponding to the seasons May to September, and October to February, 
each representing also the mean of five years of hourly observation, bears a striking 
general resemblance to those of the preceding figure ; the principal minor modifica- 
tions also are such as may readily be imagined to be occasioned by the greater- 
distance of the Cape from the dividing line. It will be remarked that the contrary 
movements at the opposite season of the year take place at the Cape of Good Hope 
as well as at St. Helena, although the sun is throughout the year to the north of 
the parallel of the Cape, and consequently is always north of its zenith. 
Having named Singapore at the commencement of this paper, I may add that I 
have examined the manuscript observations of that station in 1841 and 1842, which 
are at the Royal Society : the observations appear to have been taken in those years 
at every second hour only, consequently the diurnal variation derivable from them is 
less complete than from an hourly record, but is quite sufficient to show that in 
general characters it corresponds with that of St. Helena and the Cape of Good 
Hope : the movement of the north end of the magnet in the months of May, June, 
July and August, is to the east until 7 or 8 a.m., followed by an immediate return to 
the west ; and in November, December, January and February, to the west until 
8 a.m., followed by an immediate return to the east : the last-named months have 
also an easterly extreme about 2 p.m., which has no similar or opposite feature in 
May, June, July and August. 
From the facts here brought forward, it may be inferred that the line which has 
been supposed to exist by the eminent authorities referred to in the commencement 
of this paper, and which should be characterized by the absence of a diurnal variation 
of the declination, will not be found upon the globe. 
MDCCCXLVII. 
i 
