250 REPORT — 1861. 



as means were wanting, whatever those opinions might be, to give practical 

 effect to them. Colonel Sykes was not at the meeting at Oxford last year, 

 and no action having been taken by the Balloon Committee, it has dropped 

 through and is extinct. 



Within a few months past Mr. Simpson, of Creraorne Gardens, has con- 

 structed a balloon at a cost of £600 (the ' Normandie'), with a sufficient 

 capacity to carry two persons to great heights, which might be available for 

 the objects of the Association. The occasion has therefore arisen when the 

 re-appointment of a Balloon Committee might take place; and as one of the 

 chief objects of the last Balloon Committee, viz. the verification of the former 

 results of the ascents undertaken by the authority of the Association, remains 

 unchanged. Colonel Sykes, with the approval of those members of the late 

 Balloon Committee with whom he has had an opportunity of conversing, will 

 move the re-appointment of the Committee with a grant of £200. 



Report on the Repetition of the Magnetic Survey of England, made at 

 the request of the General Committee of the British Association. 

 By Major-General Edward Sabine, R.A., President of the Royal 

 Society. 



The Magnetic Survey of the British Islands, corresponding to the epoch of 

 January 1, 1837, which had been undertaken in 1836 at the request of the 

 British Association, was completed in 1838, and a coordinated Report of the 

 observations of the Dip and Force, contributed by each of the five Members of 

 the Association who had cooperated in the execution of the Survey, was pub- 

 lished in the annual volume for 1838, accompanied by Maps of the Isoclinal 

 and Isodynamic Lines embodying tiie results of the Survey. The observa- 

 tions of the third element, the Declination, which were made chiefly by one 

 of the cooperators, Sir James Clark Ross, were not published until a later 

 date, when, having been reduced and coordinated by myself, they were 

 included in a memoir printed in the Philosophical Transactions for IS^Q, 

 entitled "On the Isogonic Lines, or Lines of equal Magnetic Declination in 

 the Atlantic Ocean in 1840," in which they completed in a very satisfactory 

 manner the N.E. portion of the map accompanying that memoir. 



The Magnetic Survey of 1837 deserves to be remembered as having been 

 the first complete work of its kind planned and executed in any country 

 as a national work, coextensive witii the limits of the state or country, and 

 embracinj; the three magnetic elements. The example thus presented was 

 speedily followed by the execution of similar undertakings in several parts of 

 the globe ; more particularly in the Austrian and Bavarian dominions, and 

 in detached portions of the British Colonial Possessions, viz. in North America 

 and India. The immediate object of such surveys is to determine for the parti- 

 cularepoch at which they are made, the positions of Lines of equal Declination, 

 Inclination, and Magnetic Force in tiie area of the Survey; the angles at which 

 the three classes of lines respectively cross the geographical meridians ; and 

 the distances in geographical miles, measured in directions perpendicular to 

 the lines, which correspond to equal increments of each of the magnetic ele- 

 ments. By the extension and multiplication of such surveys far more satis- 

 factory materials are supplied for the construction of general magnetic maps 

 of the globe than are afforded by the desultory observations which had pre- 

 viously formed their only basis. This, as already stated, is the immediate 

 object of such Surveys; but they have in prospect another and a scarcely less 

 important purpose, in contributing by their repetition at stated intervals to 



