274 Memoir on Indian Earthquakes. [No. 136. 



and shaken violently. A succession of waves flow along the course of 

 the disturbed body, following each other rapidly until the moving force 

 is withdrawn, and thus it appears to have been with the Earthquake 

 under review. A series of great waves were generated on the 19th, 

 and propagated, with an undulatory motion to a great distance, and series 

 of smaller ones continued for upwards of a month afterwards to be con- 

 tinually formed, but propagated only to a very limited extent, but all in 

 the same direction with the first mentioned. 



As some remarkable instances of disturbance of the magnetism of 

 the earth are recorded to have occurred during Earthquake shocks, it 

 struck me that similar phenomena might possibly have been observed 

 on the present occasion at the Simla Magnetic Observatory, and I there- 

 fore wrote to Major Boileau of Engineers, the Superintendent, on the 

 subject, and he was kind enough to reply as follows, under date 5th 

 November, 1842: — 



" The magnetometers have been watched with great care during 

 (i. e. on and after) the occurrence of Earthquakes, and there never has 

 been any disturbance in their mean readings, though the mechanical 

 effect has been apparent by the vibrating motion communicated to the 

 instruments. The delicacy of our magnetic instruments is such, that 

 a movement equal to two seconds of arc would be detected immediately, 

 and I hold the total absence of any such indications, as almost amount- 

 ing to proof, that Earthquakes are not magnetic phenomena." 



If the observations at the Simla Observatory are to be held as 

 decisive on the point, then certainly it is a just inference, that no con- 

 nection exists between Earthquakes and disturbances of terrestrial 

 magnetism; but as these observations may be opposed by numerous 

 others indicating distinctly I think, such a connection, although the 

 precise nature of it is yet mysterious, Major Boiieau's inference must be 

 looked upon as premature, and his observations prove, it appears to 

 me, nothing more than, that at Simla, the Earthquakes have hitherto 

 produced effects only mechanical, but it by no means thence follows, 

 that Earthquakes generally are not in any respect magnetic pheno- 

 mena. The question is still an obscure one, and the observations 

 which have led to the impression that the causes of Earthquakes are 

 connected with terrestrial magnetism have been made chiefly in dis- 

 tricts where volcanic forces are in actual operation, and where the 



