MAGNETIC DISTURBANCES AT SEVERAL OBSERVATORIES. 
137 
With regard to the scale values in Table III., we may note that the values of H.F. 
and V.F. in metric units, for 1 mm. of height of scale, and the values of H.F. and 
Y.F. in centimetre-gramme-second units for 1 cm. of height of scale, are expressed by 
the same number. Thus, in the Kew curves, the values of H.F. and V.F. in metric 
units for 1 mm. of height of scale is '0005 unit, and the values of H.F. and V.F., for 
1 cm. of height of scale is '0005 in c.g.s units. 
Hence, in comparing past measurements in metric units, with 1 mm. for unit of 
height, with measurements in c.g.s. units, taking 1 cm. as unit of height, there will 
be very little trouble, as the scale values in the two sets of units are expressed by the 
same number. 
Hence, in future, it will be advisable for the sake of comparison, and, at the same 
time, more in accordance with the c.g.s. system of units, to state the scale values under 
the form, 1 cm. = '0005 c.g.s. units. 
On comparing the traces for H.F. from different observatories (see Plate 8) it will 
be seen that the trace from Stonyhurst shows what may at first be regarded as a very 
slight disturbance, and, at 3.48 A.M., the maximum disturbance appears to be com¬ 
paratively small, but from Table III., it will be seen that the actual disturbance is as 
large, or even larger, than at any other station except Toronto. 
There is every reason to suppose that the trace at Stonyhurst would have shown 
the individual features of the storm quite as well as the Colaba, or the Kew, or the 
Lisbon traces, if the scale value, '0005, had then been in use instead of the scale 
value '0022, and the measurements could then have been made with much greater 
accuracy. On the other hand, the vertical force magnetometer at Stonyhurst is very 
much more sensitive than that at any other station, and the trace is very similar in 
character to the St. Petersburg V.F. trace. At 3.48 a.m. there is very little disturb¬ 
ance at Kew, and a small disturbance in y.F. at Stonyhurst, viz., a fall of '001 metric 
unit. 
The y.F. trace for Batavia is placed near to the Stonyhurst trace in Plate 8, but, 
as is shown in Table III., the sudden fall in y.F. at Batavia, at 10.32 p.m., on the 24th, 
is nearly four times as great; and at 3.48 A.M., on the 25th, is more than four times 
the corresponding fall in y.F. at Stonyhurst. 
As Batavia is south of the equator, a diminution of the vertical force means a 
change in the direction of the needle corresponding to an increase of dip of the pole 
pointing towards the north ; hence, for comparison with stations in the northern 
hemisphere, the Batavia y.F. trace inverted is also given in Plate 8. 
The disturbance in V.F. is very much smaller than the disturbance in H.F., at all 
stations except Toronto, Batavia, and Melbourne. At Utrecht, the disturbance in 
y.F. nearly resembles the disturbance in declination, and is much greater apparently 
than the y.F. disturbances at Wilhelmshaven, or at any other observatory in 
the north-west of Europe. Unfortunately, the photographic paper on which the 
traces are taken is too narrow, and so the H.F. trace passes off the paper during the 
MDCCCXCII.—A. T 
