6 REPORT — 1842. 



of survey and exploration, but in ships pursuing ordinary tracks, so as at 

 length to furnish data for the construction of complete magnetic sea-charts, 

 founded on observation alone, for these important elements, as well as for 

 the declination. 



For the formation of such charts, however, it is necessary to eliminate the 

 influence of the ship's iron, an influence which the continually increasing 

 quantity of iron on board of vessels renders an evil of great and increasing 

 magnitude. Instructions for this purpose, as regards the declination, have 

 also been issued by the same authority, founded on the experience obtained in 

 our arctic expeditions, and embodied in rules which are substantially the same 

 with those given by Col. Sabine in his paper in the Phil. Trans, on Compass 

 Deviations on board the Isabella and Alexander in the arctic voyage of 1818, 

 consisting in simultaneous sea and shore observations, and reciprocal bearings 

 with the ship's head laid in succession round every point of the compass. 



In reference to contributions made to our knowledge of the magnetic ele- 

 ments in various parts of the globe, it would be unjust to omit the mention 

 of the. valuable series of such determinations made by Captain Belcher, R.N., 

 of H. M. S. Sulphur. These determinations, the first portion of which have 

 been reduced by Col. Sabine, and published in the Phil. Trans, for 1841, 

 have been continued by Captain Belcher at more than 20 stations in the 

 islands and coasts of the Pacific and China Seas. The observations are 

 arrived in England, and will shortly be reduced, forming altogether a very 

 valuable contribution towards the data accumulating for the revision of the 

 numerical elements of Gauss's Theory. 



Still less pardonable would it be in this Report to omit signalizing the final 

 publication during the last year of Professor Erman's magnetic results in his 

 journey into Siberia and voyage round the world. It is true that these results 

 are already in part interwoven with the numerical computations of M. Gauss's 

 magnetic coefficients, and so constitute an integrant part, and a most import- 

 ant one, of that vast and laborious work. But this has been by the especial 

 favour and liberality of that eminent traveller, in placing at the disposal of 

 those engaged in theoretical researches, results to them invaluable, and which 

 have actually proved most useful even without that final revision and labo- 

 rious reduction which he has ultimately given to them. When we consider 

 the vast extent of sea and land traversed by this indefatigable traveller, his 

 long residence in the dismally cold and inhospitable regions of Siberia, the 

 infinite labour of the observations themselves, and the care with which they 

 have been made, we shall see reason to regard this work as one which must 

 constitute an epoch in the history of magnetic science, both for the mass of 

 information it contains and the personal devotion it indicates. 



5. Magnetic Disturbances. 



M. Gauss truly remarks, that " It is one of the great results of British 

 enterprise, that the existence of disturbances extending over the whole globe has 

 been ascertained." As a physical fact deeply connected with the general 

 causes of terrestrial magnetism, this is indeed a result of the first magnitude ; 

 and its consideration under all its circumstances, and especially as modified 

 by distance and geographical locality, is eminently calculated to lead to spe- 

 culations on those causes, and to theoretical views tending to connect these 

 abrupt variations with the usual course of the magnetic phaenomena. To dis- 

 connect, in the phaenomena of the magnetic storms, what is local from what 

 is general, and to trace individual shocks occurring in them from observa- 

 tory to observatory, and from station to station, until they become so far en- 

 feebled by the effects of distance from their origin as to be confounded and 



