MAGNETISM. 185 



irregular manifestation of the terrestrial force is detected by 

 uninterrupted and simultaneous observations. A variation of 

 40 { 00 of the magnetic intensity is measured, and, at certain 



a Prony's magnetic telescope, suspended in a glass case by a thread 

 devoid of torsion, allowed angles of seven or eight seconds to be read off 

 on a finely divided scale, placed at a proper distance, and lighted at 

 night by lamps. Magnetic perturbations (storms), which occasionally 

 recurred at the same hour on several successive nights, led me even then 

 to desire extremely that similar apparatus should be used to the east and 

 west of Berlin, in order to distinguish general terrestrial phenomena 

 from those which are mere local disturbances, depending on the inequality 

 of heat in different parts of the Earth, or on the cloudiness of the atmo- 

 sphere. My departure to Paris, and the long period of political dis- 

 turbance that involved the whole of the west of Europe, prevented my 

 wish from being then accomplished. Oersted's great discovery (1820) 

 of the intimate connexion between electricity and magnetism again 

 excited a general interest (which had long flagged) in the periodical 

 variations of the electro-magnetic tension of the Earth. Arago, who 

 many years previously had commenced in the observatory at Paris, with 

 a new and excellent declination instrument by Gambey, the longest 

 uninterrupted series of horary observations which we possess in Europe, 

 showed, by a comparison with simultaneous observations of perturbation 

 made at Kasan, what advantages might be obtained from corresponding 

 measurements of declination. When I returned to Berlin, after an 

 eighteen years' residence in France, I had a small magnetic house erected 

 in the autumn of 1828, not only with the view of carrying on the work 

 commenced in 1806, but more with the object that simultaneous ob- 

 servations at hours previously determined, might be made at Berlin, Paris, 

 and Freiburg, at a depth of 35 fathoms below the surface. The simul- 

 taneous occurrence of the perturbations, and the parallelism of the move- 

 ments for October and December, 1829, were then graphically repre- 

 sented. (Pogg. Annalen, bd. xix., s. 357, taf. i.-iii.) An expedition 

 into Northern Asia, undertaken in 1829, by command of the Emperor 

 of Kussia, soon gave me an opportunity of working out my plan on. 

 a larger scale. This plan was laid before a select committee of one of 

 the Imperial Academies of Science, and, under the protection of the 

 Director of the Mining Department, Count von Cancrin, and the ex- 

 cellent superintendence of Professor Kupffer, magnetic stations were 

 appointed over the whole of Northern Asia from Nicolajeff, in the line 

 through Catharinenburg, Barnaul, and Nertschinsk, to Pekin. 



The year 1832 (Gottinger gelehrte Anzeigen, st. 206) is distinguished 

 as the great epoch in which the profound author of a general theory of 

 terrestrial magnetism, Friedrich Gauss, erected apparatus constructed 

 on a new principle, in the Gottingen Observatory. The magnetic 

 observatory was finished in 1834, and in the same year Gauss distributed 

 new instruments, with instructions for their use, in which the celebrated 

 physicist, Wilheim Weber, took extreme interest, over a large portion of 



