178 COSMOS. 



every direction over the Earth's surface.*- In the former case, 

 the simultaneous manifestation of the storm may serve, with- 

 in certain limitations, like Jupiter's satellites, fire-signals, and 

 well-observed falls of shooting stars, ibr the geographical 

 determination of degrees of longitude. We here recognize 

 with astonishment that the perturbations of two small mag- 

 netic needles, even if suspended at great depths below the 

 surface, can measure the distances apart at which they are 

 placed, teaching us, for instance, how far Kasan is situated 

 east of Gottingen or of the banks of the Seine. There are 

 also districts in the earth where the mariner, who has been 

 enveloped for many days in mist, without seeing either the 

 sun or stars, and deprived of all means of determining the 

 time, may know with certainty, from the variations in the 

 inclination of the magnetic needle, whether he is at the north 

 or the south of the port he is desirous of entering.! 



* There are also perturbations which are of a local character, and 

 do not extend themselves far, and are probably less deep-seated. Some 

 years ago I described a rare instance of this kind, in which an extraor- 

 dinary disturbance was felt in the mines at Freiberg, but was not per 

 ceptible at Berlin. (Lettre de AI. de Humboldt a Son Altesse Royale le 

 Due de Sussex sur les moyens propres a perfectionner la Connaissance 

 iu Magnetisme Terrestre, in Becquerel's Trait6 Experimental de V Elec~ 

 'ricitf, t. vii., p. 442.) Magnetic storms, which were simultaneously 

 r elt from Sicily to Upsala, did not extend from Upsala to Alten. (Gauss 

 and Weber, Resultate des Magnet. Vereins, 1839, 128; Lloyd, in the 

 Complex Rendus de VAcad. des Sciences, t. xiii., 1843, Sem. ii., p. 725 

 and 827.) Among the numerous examples that have been recently 

 observed, of perturbations occurring simultaneously and extending over 

 wide portions of the Earth's surface, and which are collected in Sabine's 

 important work (Observ. on Days of unusual Magnetic Disturbance, 

 1813), one of the most remarkable is that of the 25th of September, 

 1841, which was observed at Toronto in Canada, at the Cape of Good 

 Hope, at Prague, and partially in Van Piemen's Land. The English 

 Sunday, on which it is deemed sinful, after midnight on Saturday, to 

 register an observation, and to follow out the great phenomena of crea- 

 tion in th^i" perfect development, interrupted the observations in Van 

 Diemen's Land, where, in consequence of the difference of the longi- 

 tude, the magnetic storm fell on the Sunday. (Obsew., p. xiv., 78, 85, 

 and 87.) 



t I have described, in Lametherie's Journal de Physique, 1804, t. 

 lix., p. 449, the application (alluded to in the text) of the magnetic in- 

 clination to the determination of latitude along a coast running north 

 nd south, and which, like that of Chili and Peru, is for a part of tho 

 year enveloped in mist (garua). In the locality I have just mentioned, 

 this application is of the greater importance, because, in consequence 

 of the strong current running northward as far as to Cape Parena, navi- 

 gators incur a great loss of time if they approach the coast to the north 

 of the haven they are seeking. In the South Sea, from Callao de Limn 

 harbor to Truxillo, which differ from each other in latitude by 3 57' 





