recently carried on in the Russian Empire. 295 



of the variations of terrestrial magnetism in the declination and 

 dip of the needle, and in the intensity of its force ; for the de- 

 clination of the needle in different countries, which is more ex- 

 clusively required by sailors, is intimately connected in theory 

 with the other two elements, the inclination and the intensity as 

 measured by oscillations. At no preceding epoch has the know- 

 ledge of the variations of terrestrial magnetism made such rapid 

 progress as within the last thirty years. The angle which the 

 needle forms with the vertical and with the meridian of a place, 

 — the intensity of the forces which I have had the good for- 

 tune to observe from the equator to the magnetic pole, — the 

 horary variations of the declination, — the inclination and the mag- 

 netic intensity often modified by the aurora borealis, earthquakes, 

 and mysterious motions in the interior of the globe, — the starts 

 or non-periodical perturbations of the needle, which, after a long 

 course of observations, I have distinguished by the name of 

 magnetic storms, have become in their turn the object of the 

 most elaborate research. The great discoveries of Oersted, 

 Arago, Ampere, Seebeck, Morichini, and Mrs Somerville, have 

 disclosed to us the mutual relations of magnetism with electri- 

 city, heat, and solar light. There are only three metals — iron, 

 nickel, and cobalt, which become loadstones. The astonishing 

 phenomenon of the magnetism of rotation, which my illustrious 

 friend, M. Arago first made known, shows us that almost all the 

 bodies of nature are transiently susceptible of magnetic action. 

 The Russian empire is the only country which is traversed with 

 two lines of no declination, — that is, in which the needle is di- 

 rected to the poles of the globe. One of these two lines, whose 

 position and periodical motion of translation from east to west 

 are the principal elements of a future theory of terrestrial mag- 

 netism, passes, according to the latest researches of MM. Han- 

 steen and Erman, between Mourom and Nijni-Novgorod ; the 

 second some degrees to the east of Irkoutsk, between Parchin- 

 skaia and larbinsk. We do not yet know their prolongation to 

 the north, or the rapidity of their motion to the west. Terres- 

 trial physics requires the complete trace of the two lines of no 

 declination at equidistant epochs, every ten years for example, 

 — the precise absolute variations of inclination and intensity in 

 all the points where MM. Hansteen, Erman, and-J, iiave ob- 



