ON THE MAGNETIC SURVEY OF ENGLAND. 251 



supply the best kind of data for the gradual elucidation of the laws and source 

 of the secular change in the distribution of the earth's magnetism, perhaps 

 the most remarlcable of the yet unexplained natural phenomena of the globe. 



It was in this view that the General Committee of the British Association, 

 assembled at Cheltenham in 1856, considering that in 1857 twenty years 

 would have elapsed since the epoch of the first Survey, passed the following 

 Resolution, — " That a Committee, consisting of General Sabine, Professor 

 Phillips, Sir James Clark Ross, Mr. Robert Were Fox, and the Rev. H. 

 Lloyd, be requested to undertake the Repetition of the Magnetic Survey of 

 the British Islands." The five members of the Association named in this Reso- 

 lution were the same by whom the former Survey had been made, and were 

 all living at the time of the Cheltenham Meeting, Dr. Lloyd and Mr. Phillips 

 being present at it. I was myself on the continent for the recovery of health, 

 but on my return in the autumn of 1856, finding my own name standing first 

 in the list of the Committee, I lost no time in making such arrangements as 

 seemed suitable for the accomplishment of the purpose which the Associa- 

 tion had in view. Dr. Lloyd undertook the Irish portion ; Scotland and the 

 islands to its North and West were placed, with the consent of the 

 Committee of the Kew Observatory, in the able hands of Mr. Welsh, the 

 Superintendent of that establishment, and a grant of £200 was obtained from 

 the Admiralty towards the payment of his travelling expenses. For some 

 time I cherished the hope that the repetition of the English Survey might be 

 accomplished (as on the previous occasion) by the joint labours of the Mem- 

 bers of the Committee : but at len{:th it became evident that circumstances 

 of health or the pressure of other employments and duties stood in the way of 

 a combined operation ; which would have ncce<sitatefi also a great amount 

 of additional labour in the intercomparison of the different instruments and 

 methods employed. I have made therefore the whole of the observations for 

 the isoclinal and isodynamic lines myself; but having only a portion of each 

 year at my disposal, they have required the summers of 1858, 1859, 1860, 

 and 1861, causing January 1, 1860, to become the middle epoch of the 

 Survey, in respect to these two of the three elements. The detail of the 

 observations, the conclusions derived from them, and the maps of the two 

 elements, constitute the two first divisions of the present Report ; the third 

 division, containing the observations upon which the map of the isogonic 

 lines for 1857 is based, together with the comparison of these lines with 

 those of the earlier Survey, and the deduction of the mean secular change of 

 this element in the interval, has been contributed by Frederick John Evans, 

 Esq., F.R.S., Superintendent of the Compass Observatory of the Royal Navy 

 at Woolwich. 



The premature decease of Mr. Welsh, accelerated it is feared by his too 

 persistent exposure in the second year of the Scottish Survey, left the reduc- 

 tion and publication of the northern portion of the British Survey to his 

 successor at Kew, Mr. Balfour Stewart, by whom a report has been presented 

 to the General Committee, which report is printed in the atmual volume for 

 1859. There remains, therefore, now, for the entire fulfilment of the desire 

 embodied in the Resolution of the General Committee at Cheltenham in 

 1856, only the Irish portion of the Survey, which has been undertaken by 

 Dr. Lloyd, to whom have been added as coadjutors, by his own request, the 

 Rev. Professors Galbraith and Haughton, and George Johnstone Stoney, Esq. 

 Dr. Lloyd has acquainted me that it is his wish, and that of the gentlemen 

 associated with liim, that the Irish portion of the Survey should be published 

 in the ' Transactions of the Royal Irish Academy.' The present is there- 

 fore the concluding Report aildressed to the British Association of the 

 Committee nominated by them at the Cheltenham Meeting in 1856. 



