44 
MR. GEORGE W. WALKER ON THE MAGNETIC RE-SURVEY OF THE 
We have now reached a stage at which a comparison between the results of the 
re-survey and those obtained by Kuckee and Thoepe is desirable. It appeared to 
me best to take the results of the 1886 survey rather than those of the more extended 
survey in 1891. Accordingly Table VII. has been drawn up to show station by station 
and district by district the change of H, D, and I, between epoch January 1, 1886, 
and January 1, 1915. 
Before discussing the differences obtained, several points must be referred to :— 
(1) Since the stations differ a little from those used by BtiCKEE and Thoepe, we 
ought strictly to introduce corrections allowing for the differences of latitude and 
longitude. In more peaceful times such a course would probably have been adopted, 
but in the present circumstances the considerable amount of computation involved 
could hardly be justified and so must be postponed till a more favourable occasion. 
(2) In view of the known differences between different instruments, I was anxious 
to find out if possible how the survey standards adopted by Buckee and Thoepe 
would compare with those adopted for the re-survey (viz., the Greenwich standards 
for 1915). So far my endeavours have not met with any success. The instruments 
used by them are either no longer available or have undergone re-organisation. 
Ruckee and Thoepe did not make any direct observation at Greenwich, and I gather 
that the values they assign to Greenwich were supplied by the Astronomer Royal 
from the observatory apparatus. 
They made comparison with the Kew observatory apparatus and found some 
discrepancy. Those in D and I were not very serious and have since been explained 
and show that in D and I their standards would not differ seriously from those in 
use at Greenwich at present. In H, however, their survey standard was 29y higher 
than the Kew standard at the time. I am not without hope that some light on the 
matter may arise from careful investigation, but not at the present time. 
These points, however, emphasize the urgent necessity of preparing an adequate 
standard of magnetic force if full advantage is to be taken of the results of the future 
surveys. I would again urge as on p. 2 that the instruments used by me in the 
re-survey should on no account suffer the same fate as those used by Ruckee and 
Thoepe, but should be*'carefully preserved for comparison with Greenwich when the 
next survey is made. 
Looking at .the differences tabulated they are on a general conspectus extremely 
satisfactory and show a remarkably uniform change all over the British Isles. I 
mean, of course, in the total change, for we know that the annual rate at any one 
place varies from time to time. There are, however, a few outstanding differences of 
considerable interest. 
The case that first attracted my notice was that of Dundee, where the increase of 
H was only 88y and the decrease of I only 12'. ’ It will be seen that the differences at 
Glasgow, Stirling and Strachur are very similar to those at Dundee. This group is 
quite unique. 
