280 
MR. A. W. RUCKER AND DR. T. E. THORPE ON A MAGNETIC 
The Eastern and South-Eastern Counties. 
A problem of con.siderable interest has to be considered in connection with the 
Eastern and South-eastern counties. In the greater part of this district, the surface 
soil is such that it certainly can produce no marked effect upon the magnet, yet in this 
apparently “good ground,” we have found magnetic disturbances of very wide range. 
It is well known that the Declinations obtained at the Kew and Greenwich 
Observatories differ more widely than the difference of longitude will explain. The 
difference is not so great as appears at first sight, as the Kew results as published are 
not corrected for diurnal variation. 
The published mean Declinations at these two stations in 1886 are, Greenwich 
17° 54'‘5, and Kew 18° 16''9, of which the Kew result must be diminished by about 6'. 
This gives a difference of 16', which exceeds that corresponding to the difference 
of longitude by 10'. We are not aware that any attempt has hitherto been made to 
connect this discrepancy between the Declinations at these two important observatories 
with any regional disturbance in their neighbourhood. 
The fact which first led us to believe that they lie within the area of such a 
disturbance was that there is not only a small decrease in the Declination between 
Kew and Reading (instead of an increase as the difference of longitude requires), but 
that there is also a very small difference between Worthing and Hyde. 
The Declination at Reading should be about 20' greater than that at Kev', but the 
observation made there in 1886 proved that it is 1' less. 
The Declination was again determined in 1888 at the same spot near Reading, with 
the result that the Declination, when reduced to epoch, came out 3'’6 lower than 
before, thus increasing the discrepancy betvveen the actual and calculated differences 
between the two stations. 
In like manner, the difference of lougitude between Ryde and Worthing is 
equivalent to a change of 22' in the Declination, whereas the observed value at Ryde 
was only 2'‘6 higher than that at the more easterly station. 
In order to investigate these differences more fully, we determined to run a chain of 
stations along the valley of the Thames, to observe at another series half-way between 
the Thames and the Channel, and to interpolate a station betw^een Worthing and Ryde. 
The result is shown in the annexed diagram (fig. 14). Horizontal lengths indicate 
the longitudes of stations and vertical lines the Declination. 
Three groups of stations, such that all places included in each are of nearly the 
same latitude are taken, thus fonninp' three lines crossinsf the whole of the south of 
England. In the cases of Weymouth and Ryde, which lie considerably to the south 
of the line which nearly passes through the other stations corrections of 14' and 7' 
respectively have been added. Chichester is to the north of the line and its Decli¬ 
nation has also been corrected by 7'. 
It will be noticed that all three exhibit an anomaly on or immediately to the south 
