SURVEY OF THE BRITISH ISLES FOR THE EPOCH JANUARY 1, 1886. 281 
of a line joining Greenwich and Reading. In the valley of the Thames the Declina¬ 
tion attains a maximum value near Windsor and a well marked minimum near 
Reading. To the south of this district there is a remarkable slackening in the rat;e 
of increase of the Declination. 
An inspection of this figure is sufficient to prove that the anomaly in the Declina¬ 
tion difference of Greenwich and Kew is not due to any accidental peculiarity of the 
position of either observatory, but is the result of a regional disturbance extending 
at least from that part of the valley of the Thames which lies between Greenwich 
and Reading to the south coast. 
1. Soiitliend 
2. Purfleet 
3. Greenwicli 
4. Kew 
5. Windsor 
6. Reading 
Declinations at— 
7. Clifton 
8. Cardiff 
9. Dover 
10. Tunbi’idge Wells 
11. Horsham 
12. Haslemere 
13. Alresford 
14. Salisbury 
15. Taunton 
16. St. Leonards 
17. Worthing 
18. Chichester 
19. Ryde 
20. Weymouth 
21. Exeter. 
The curves in the diagram when compared with figs. 7 and 8 (p. 263) are seen to be 
such as would be produced if a centre of force attracting the north-seeking pole of a 
magnet were situated near Windsor. Immediately over such a centre the value of 
the Declination would be normal, while it would be too great and too small at stations 
to the east and west respectively. If the centre were relatively weak the increase in 
the Declination with longitude instead of being represented by the slope of a straight 
line would be given by a curve of the same type as that in fig. 7, if it were strong we 
should have a curve like that in fig. 8. 
MDCCCXC.—A, 2 0 
Ucdinaticm 
