of Terrestrial Magiietism. 49 



globe. He employed the same instruments and tlae same me- 

 thods which he had made use of from Berlin to the mouth of 

 the Oby, and thence to the Sea of Okhotsk. 



That which characterizes our epoch, at a time distinguished 

 by grand discoveries in optics, electricity, and magnetism, is 

 the possibility of connecting phagnomena by the generalization 

 of empirical laws, and the mutual aid afforded by sciences 

 which had long remained isolated. At the present day simple 

 observations upon horary declination or magnetic intensity, 

 made simultaneously in situations very distant from each other, 

 reveal, so to speak, what passes at profound depths in the 

 interior of our planet, and in the superior regions of the at- 

 mosphere. The luminous emanations, the polar explosions 

 which accompany the magnetic storm, appear to follow great 

 changes in the habitual or mean tension of terrestrial mag- 

 netism. 



It would tend greatly to promote the advancement of the 

 mathematical and physical sciences if, under the Presidency 

 and auspices of Your Royal Highness, the Royal Society 

 of London, to which I make it my boast to have belonged for 

 twenty years, would exert its powerful influence to extend the 

 line of simultaneous observations, and to establish permanent 

 magnetic stations, either in the region of the tropics, on each 

 side of the magnetic equator, the proximity of which neces- 

 sarily diminishes the amplitude of the horary declinations, or 

 in the high latitudes of the southern hemisphere and in Ca- 

 nada. I venture to propose this latter point, because obser- 

 vations upon horary declination made in the vast extent of the 

 United States are still very rare. Those, however, of Salem, 

 in 1810, calculated by Mr. Bowditch, and compared by Arago 

 with the observations of Cassini, Gilpin, and Beaufoy, merit 

 great praise, and might serve as a guide to observers in Ca- 

 nada in investijiating whether the declination there does not 

 diminish between the vernal equinox and the summer solstice, 

 contrary to what occurs in Western Eui'ope. In a memoir 

 that I published five years ago, I suggested as magnetic sta- 

 tions extremely favourable to the progress of our knowledge. 

 New Holland, Ceylon, the Mauritius, the Cape of Good 

 Hope (rendered illustrious by the labours of Sir John Her- 

 schel), St. Helena, and some point on the eastern coast of 

 America to the south of Quebec. In the last century, in the 

 years 1794 and 1796, an English traveller, Mr. Macdonald, 

 made some new and important observations upon the diurnal 

 motion of the needle at Sumatra and St. Helena, which have 

 since been confirmed and extended upon a large scale in the 

 scientific expeditions of Captains Freycinct and Duperrey ; 



Third Series. Vol. 9. No. 51. Jiili/ 1836. H 



