Professor de la Rive wi Electricity. 271 



tions of the intensity of terrestrial magnetism. But the most of 

 them are collected in the Annales de Chimie et de Physique, 

 t. xxxix., where they have been regularly published by M. Arago, 

 who has himself engaged in an interesting discussion on the sub- 

 ject, in answer to some objections which had been made to his 

 views by Dr Brewster. 



Though obliged to pass by many of the researches on the 

 phenomena of terrestrial magnetism, we wish siill to mention 

 those which some American naturalists have undertaken on the 

 declination of the needle in the United States ; and also the ob- 

 servations of M. Quetelet upon the measure of the magnetic in- 

 tensity in different places in Germany, the Netherlands, of 

 Switzerland and Italy. The former lead to consequences alto- 

 gether similar to those which Europeans, and especially M. 

 Hansteen, have drawn from their observations. The latter, 

 those of M. Quetelet, executed with unusual care, afford the 

 horizontal intensity of terrestrial magnetism, for a great num- 

 ber of places in the countries named above ; and as it regards 

 the total intensity, it can be determined only for those of the 

 places where the magnetic dip is known. The horizontal in- 

 tensity goes on increasing as we approach the south, a natural 

 consequence of the diminution of the dip ; the total intensity, 

 on the contrary, in spite of one or two anomalies, seems to in- 

 crease as we advance northwards. We take leave, on the point of 

 these magnetic intensities, to allude to the remarkable coincidence 

 which M. Necker de Saussure has found to exist between the 

 direction of curves of equal magnetic intensity, and that of the 

 stratification of the principal chains of mountains, and of the 

 physiognomy of continents *. This relation which M. Necker 

 has succeeded in establishing with much precision, supporting it 

 upon the numerous magnetic observations with which science 

 has been enriched for several years, and especially those of M. 

 Hansteen, is assuredly not a circumstance purely fortuitous, 

 and presents much to interest in a geological as well as in a 

 philosophical point of view. 



The examination which we have just made of the results 

 to which observations on terrestrial magnetism have hitherto 

 led, however rapid it may have been, is nevertheless sufficient 



• Bibl. Univ. t. xliii. p. 166. 



t2 



