Xxiv SIXTH REPORT — 1836. 



the prosecution of these researches, and has proposed to obtain for them 

 the national assistance. To call the attention therefore of the scientific 

 world, in a greater degree, to the present condition of our knowledge 

 as to Terrestrial Magnetism, was the object of Captain Sabine's Report 

 in the present volume of these Transactions; and this he has accom- 

 plished by presenting us with an elaborate abstract of the work which 

 Professor Hansteen, of Copenhagen, had published upon that subject. 



This mathematician, in the year 1811, constructed a chart, in which 

 were laid down, so far as could be ascertained, the lines of equal varia- 

 tion and dip of the magnetic needle in all parts of the world. It is 

 curious to observe the degree of coincidence which exists between these 

 lines representing the distribution of the magnetic force, and the iso- 

 thermal lines by which Humboldt has expressed the distribution of heat 

 over the earth's surface ; and this apparent connexion, the cause of which 

 remains a mystery, is calculated to stimulate our zeal for investigating 

 the phenomena of both. Nor is it less interesting to trace in what de- 

 gree these later observations appear to confirm the general conclusions 

 arrived at by the celebrated Halley more than a century before. That 

 astronomer had inferred, from a general review of all that was then 

 known with regard to the variation and dip of the needle, that there 

 must be two magnetic axes ; whilst the gradual shifting of the line of 

 no variation from west to east, led him to propose the ingenious, though 

 whimsical hypothesis, of a moveable globe existing in the interior of the 

 earth we inhabit, actuated by the same forces as those which propel the 

 hollow sphere surrounding it, and, like it, possessing a north and south 

 magnetic pole. This interior globe, if it be supposed to move with 

 somewhat less rapidity than the exterior shell, might, as he conceived, 

 produce a gradual shifting of the poles from east to west, and thus ac- 

 count for the difference observed from time to time in the position of 

 the magnetic axes. 



Now the researches of Professor Hansteen confirm the existence of 

 two magnetic axes, though they led him to discard the hypothesis by 

 which Halley accounted for the progressive shifting, which, indeed, the 

 recently-discovered connexion between Electricity and Magnetism gives 

 us hopes of explaining more satisfactorily, as has been shown by Pro- 

 fessor Christie in the Report read by him at our third meeting. 



Since the publication, however, of the great work to which his Mag- 

 netic Chart is appended. Professor Hansteen, aware of the mystery 

 which still overhangs the subject, has been zealously employed in at- 

 tempting to remove it, by ascertaining the present state and progressive 

 change of the magnetic forces. He has accordingly employed himself 



