318 Report on Terrestrial Magnetism. 



John Herschel, with reference to observations of the barometer 

 and thermometer. 



Referring in terms of commendation to the magnetical obser- 

 vations which have originated in this country, M. de Humboldt 

 expresses his wish that such observations may, by the adoption 

 of an uniform plan, and by connecting them with the observa- 

 tions now in progress on the continent of Europe and of North- 

 ern Asia, be rendered more proper for the manifestation of great 

 physical laws. He then enters into an historical detail of the 

 establishment of stations for magnetical observations, stating the 

 important results obtained by MM. Aragoand Kupffer by means 

 of simultaneous observations, which appear to establish the iso- 

 chronism.of the perturbations of the needle at Paris and Kasan, 

 stations separated by 47 of longitude. Under the patronage of 

 the Governments of France, of Prussia, of Denmark, and of 

 Russia, magnetical observatories have been established at Paris, 

 at Berlin, in the mines of Freyberg, at Copenhagen, in Iceland, 

 at St Petersburgh, Kasan, Moscow, Barnoui at the foot of the 

 Altai Chain, Nertschintk near the frontiers of China, even at 

 Pekin, and at Nicolajeff in the Crimea. 



M. de Humboldt states that the lines representing the horary 

 variations at Berlin, Freyberg, Petersburgh, and Nicolajeff affect 

 parallelism, notwithstanding the great separation of the stations 

 and the influence of extraordinary perturbations ; that this, how- 

 ever, is not invariable, since even at small distances, for example, 

 at Berlin and in the mines of Freyberg, one of the needles may 

 shew considerable perturbations, while the other continues that 

 regular course which is a function of the solar time of the place. 



The epochs at which it had been proposed that simultaneous 

 observations should be made at all stations were, 

 20th and 21st of March, 



4th and 5th of May, 



From 4 o'clock in the morning of the 



21st and 22d of June, ^ ^ untu ^ of 



6th and 7th of August, cond O i servi at least hourl . ht 



23d and 24th of September, 



and day, at each magnetic station. 

 5th and 6th of November, 



21st and 22d of December, 

 But as many observers have considered these as too near to each 

 other, the observations most to be insisted upon are those at the 

 times of the solstices and equinoxes. 



