MAGNETIC PHENOMENA AT THE KEW OBSERVATORY. 
309 
In the Vertical Force. 
Year ending December 31, 1859 . . . 
. 540-235 inches. 
55 55 
1860 . . . 
. 364-208 
55 
55 55 
1861 . . . 
. 226-625 
55 
55 55 
1862 . . . 
. 358-756 
55 
55 55 
1863 . . . 
. 174-712 
55 
55 55 
1864 . . . 
. 238-597 
55 
Total 
in the 6 years 
. 1903-133 
55 
Mean Annual Value - 317'189 
6 
Hence it appears that of the years comprised in the Record, 1859 was manifestly the 
year of greatest disturbance both in the Horizontal and Vertical Forces; and 1863, or 
we might say 1863 and 1864, the year or years of least disturbance*. 
I proceed to the details in the different years : — 
Horizontal Force Disturbances, from 1st January 1858 to 31st December 1864. 
The number of the Bifilar observations in which the amount of disturbance equalled 
or exceeded T50 inch in the 7 years was 5932, being about 1 in 10 of the whole body 
of the observations taken from the traces (60491). 
* The earliest indication of what is now so generally recognized as “ the Disturbance Period of the Magnetic 
Variations” is derivable from Abago’s Observations of the Declination in Paris, commenced in 1820 and 
terminated in 1830. [Editor’s Note, pages 355-357, in the English translation of Metereological Essays by 
Fean§ois Abago (Longman), 1855.] The Epoch of Minimum shoAvn by those observations occurred in 1823-24, 
and the Epoch of Maximum in 1829. The annual increase was progressive and continuous from the mini- 
mum to the maximum; and the years preceding 1823 and following 1829 showed portions of a corresponding 
variation. 
From the period of the establishment of the British Colonial Observatories in 1841, however, we may date the 
existence of a more full and systematic investigation of the phenomena of the Decennial Magnetic Variation, not 
limited to a single element, viz. the Declination, as in the case of M. Abago’s observations, but including also the 
phenomena of the Horizontal and Vertical Forces, observed or recorded by suitable methods. From the con- 
current testimony obtained from localities widely separated from each other, such as Toronto in Canada, Hobarton 
in Tasmania, Munich in Germany, and Girard College in the United States of America, we have learnt that 
1843-44 was an Epoch of Minimum, and 1848-49 an Epoch of Maximum Disturbance in each of the three 
Magnetic Elements. The further evidence contained in this paper, derived from the Automatic Records of the 
Horizontal and Vertical Forces at the Ivew Observatory, shows that 1858-59 was also an Epoch of Maximum, 
and 1863-64 an Epoch of Minimum. 
The facts thus brought together exhibit an accordance (too close to be regarded as accidental) with the 
Decennial Variation in the phenomena of the Solar Spots observed by Hoebath Schwabe, Hon. F.R.S., as 
announced by himself in the following words : — “ The numbers in the accompanying Table leave no doubt that 
from 1826 to 1850 the occurrence of spots has been so far characterized by periods of ten years, that its maxima 
have fallen in 1828, 1837, 1848, and its minima in 1833 and 1843.” [Humboldt’s Cosmos (Longman), vol. iii. 
pages 291 and 292.] 
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