548 
MR. W. ELLIS ON THE RELATION BETWEEN MAGNETIC DIURNAL 
instruments were situated in the original “ upper magnet room ” of the Magnetical and 
Meteorological Observatory—a room subject to the ordinary changes of temperature of 
an above-ground apartment. But on completion of the new magnetic basement, 
excavated under the old magnetic building in the year 1864, the instruments were 
moved to this new room, in which the diurnal range of temperature is, on the average, 
less than 1°. The advantage of the latter location of the instruments is evident; it has 
undoubtedly tended to give greater smoothness to the results. That those of the 
horizontal force instrument should show improvement was likely, but that the 
improvement should extend also to the results for declination seems to indicate that 
some general causes of disturbance, other than the direct action of temperature, are 
avoided by the location in a room kept at a more uniform temperature. 
On further comparing together the curves, the general flatness of the 1860 
maximum in all three curves, and the opposite sharpness of the 1870 maximum, are 
noteworthy ; the maximum of 1848 occupies in this respect an intermediate position. 
The rise from the epoch of minimum to that of maximum appears to be particularly 
rapid. And in all three cases of descent from the epoch of maximum to that of minimum 
there occurs a greater or less check in the fall of the curve, and sometimes even a second 
small rise. The near coincidence hr the check in the rise in 1869, and in the fall in 
1872, shown in both cases in all three curves, seems also remarkable. 
If we select the extreme points of the curves we obtain the following epochs of 
minima and maxima. 
Table III.— Epochs of minima and maxima of extreme points of the curves. 
Epoch. 
Sun-Spot 
Epoch. 
Excess above Sun-Spot Epoch. 
Phase. 
Declination. 
Horizontal 
Force. 
Mean 
Magnetic 
Effect. 
Declination. 
Horizontal 
Force. 
Mean 
Magnetic 
Effect. 
[Minimum 
1844-3 
1842-9 
1843 "60 
1843-5 
y 
+ 0-8 
y 
— 0-6 
y 
+o-io 
Maximum . 
1848-1 
1849-0 
1848-55 
1848-1 
o-o 
+ 0-9 
+ 0-45 
Minimum 
1857-2 
1855-1 
1856-15 
1856-0 
+ 1-2 
-0-9 
+ 0-15 
Maximum . 
1860-6 
1860-2 
1860-40 
1860-1 
+ 0'5 
+o-i 
+ 0-30 
Minimum 
1867-5 
1867-6 
1867-55 
1867-2 
+ 0-3 
+ 0-4 
+ 0-35 
Maximum . 
1870-8 
1870-9 
1870-85 
1870-6 
+ 0-2 
+ 0-3 
+ 0-25 
Mean Excess at Epocli of Minimum .... 
+ 0-77 
-0-37 
+ 0-20 
Mean Excess at Epoch, of Maximum.... 
+ 0-23 
+ 0-43 
+ 0-33 - 
General Mean Excess 
+ 0-50 
+ 0*03 
+ 0-27 
If we take differences between the successive epochs of minimum and maximum of 
the mean magnetic effect we obtain the intervals 
y y v y y 
4'95 7 ; 60 4-25 7 : 15 3‘30 
