SURVEY OF THE BRITISH ISLES FOR THE EPOCH JANUARY 1, 1886. 
81 
Secular Corrections. 
The secular correction is often appreciably different at neighbouring stations. Thus 
the annual change in tlie Dip in the years 1883-4 and 1884-5 was 1'’8 and 1''7 at 
Greenwich, and I'A and 1'’2 at Kew. 
The differences in the Declination change are still more marked, as the following 
Table shows. 
Year. 
Declination. 
Annual variation. 
Greenwicli. 
Kew. 
Greenwicli. 
Kew. 
1880 . 
18 32-6 
18 59'0 
5-5 
8-5 
1881. 
27T 
50-5 
4-8 
57 
1882 . 
22-3 
44*8 
7-3 
4-8 
1883 . 
150 
40-0 
7‘4 
8-0 
1884 . 
Y6 
32-0 
5-9 
7*3 
1885 . 
17 
247 
It will be noted that the annual variations differed in 1880 by 3''0, and that the 
average difference irrespective of sign is 1''4. 
It does not therefore appear advisable to reduce the observations to one epoch by 
means of the annual variations as determined at a single observatory. 
On the whole a better result will probably be attained if we collect all the evidence 
at our disposal and deduce from it an average secular change. 
The comparison of our own observations with those of Mr. Welsh affords the 
means of determining this quantity for Scotland, and proves that the rate of decrease 
of the Dip is less in the northern than in the southern stations, a result which is in 
accord with previous observations. 
The mean decrease in Scotland between 1837 and 1857 was 1''94. (‘Brit. Assoc. 
Hep.,’ 1859, p. 169.) In the nearly corresponding interval between 1837 and 1860 it 
was 2'’05 on the northern border of England and 2'‘68 on the south coast. (‘ Brit. 
Assoc. Rep.,’ 1861, p. 260.) 
Unfortunately very few Dip observations were made in England and none were 
made in Ireland in the 1857 survey, but there are a number of stations common to 
the surveys of 1837 and 1886. We can thus determine the secular decrease during 
the last 50 years. In the following Table the stations ai'e grouped according to their 
geographical distribution, the districts being North and South Scotland, North, 
Central, and South England and Wales, and North and South Ireland. 
The data for the 1837 survey are taken from the paper by the late Sir Edward 
Sabine, already cited (‘ Phil. Trans.,’ 1870, Vol. 160, p. 271). 
MDCCCXC.—A. 
M 
