SURVEY OF THE BRITISH ISLES FOR THE EPOCH JANUARY 1, I8!)|. 
0-29 
would allow. At other places we can only account for the irregularities by slight 
dilferences in the positions of the stations or by real changes in the Disturbing Forces. 
(3.) Secular Change from Magnetic Observatories. 
The third group of data at our disposal for the determination of the secular change 
is furnished by the magnetic observatories. 
There are now five of these in the United Kingdom, viz. : Greenwich, Kew, Stony- 
hurst, Valentia, and Falmouth. 
Observations were not made regularly at the two last till after 1886, so that they 
do not provide a measure of the secular change from 1886-91. 
As Greenwich and Kew are very near together, and as the final results of the 
Greenwich observations for 1891 were not published at the end of 1892, when the 
secular change was being calculated, we have depended only on Kew for the south of 
England, and on Stonyhurst for the north. 
The data for Stonyhurst were kindly supplied to us by the Rev. W. Sidgkeaves, 
and are given below, together with those for Kew. 
Table of Secular Change from January, 1886-91, at Kew and Stonyhurst. 
Year. 
Declination. 
D 
ip. 
Horizontal force. 
Kew .... 
1886 
18 16-3 
O 
66 
37-4 
1-8093 
1891 
17 45-7 
67 
31-8 
1-8184 
- 30-6 
- 6-6 
91 
Stonyhurst. 
1886 
19 42-0 
69 
12-5 
1-7002 
1891 
19 9-7 
69 
6-9 
1-7072 
- 32-3 
- .5-6 
70 
Having thus collected all the data which seemed likel}'’ to be useful, we prepare(l 
a table of the secular change at the intersection of lines corresponding to whole degrees 
of latitude and longitude, whicli give a tolerably regnlar variation of the change over 
the whole country, and also agree as nearly as may be with the results of observation 
as deduced from the central stations, repeat stations, and observatories. 
This table is given below. In each square corresponding to a given degree of lati¬ 
tude and longitude is the secular change for five years of the Declination, Dip, 
and Horizontal Force. Signs are omitted. Forces ai'e e.xpressed in terms of O'OOOl 
metric or O'OOOOl C.G.S. unit. Declinations and Dips in minutes of arc. 
3 y 
MDCCCXCVI.—A 
