PHILOSOPHICAL TRANSACTIONS. 
The Magnetic Re-survey of the British Isles for the Ejwch January 1, 1915. 
By George W. Walker, A.B.C.Sc., M.A., F.R.S., formerly Fellow of 
Trinity College, Cambridge. 
Received June, 1917. 
[Plates 1-5 and Diagrams 1-6.] 
The first Magnetic Survey of the British Isles by Pucker and Thorpe was reduced 
to epoch January 1, 1886, and their more extended survey was reduced to epoch 
January 1, 1891. For some years a revision of the original survey had been 
contemplated by Sir Arthur Rucker, but for various reasons did not mature. In 
the summer of 1913 the Royal Society decided to repeat the survey of the main 
magnetic features of the British Isles obtained by Rucker and Thorpe, and invited 
me to undertake the work. 
It would in any case have been an honour to carry out this work, but to me the 
honour was increased by the fact that I was a pupil of Sir Arthur Rucker and 
Sir Edward Thorpe, at the Royal College of Science, when their great undertaking 
was .nearing its completion. The Royal Society desired that I should consult 
Sir Arthur Rucker with regard to the general scope of the new survey; and, 
fortunately. Sir Arthur was able at the time to enter into the matter both by 
correspondence and by personal interview. His view was that the original 200 points 
used by him and Sir Edward Thorpe should be re-determined and, if possible, 
marked in some permanent way. He further desired that about 40 new points along 
the Yorkshire “ ridge line” should be chosen. 
We discussed the question of apparatus, and the strongest arguments were in 
favour of using the same type of apparatus as before, viz., a Kew Unifilar and a Dover 
Dip-Circle. I proposed to reduce all values to Greenwich Observatory as theoretical 
base station, but to have my working base at Cambridge Observatory. In surveying 
parlance Cambridge Observatory was thus to be a satellite station referred to 
Greenwich Observatory. Sir Arthur warmly approved of this proposal, and it was 
most cordially entertained by the Astronomer Royal, Sir Frank Dyson, and by 
Prof. H. F. Newall, who was then acting for Sir Pv,obert Ball. 
On many preliminary points I received much invaluable advice from Sir Arthur 
Rucker, and I had looked forward to having his help and guidance throughout the 
work which is now (May, 1917) nearly complete. Alas, my interview with him in 
1913 proved to be the last, as soon after he was struck down by serious illness. 
Although I know from Lady Rucker that he retained a lively interest in the 
VOL. CCXIX.-A 570. B [PubUslied, August 7, 1919. 
