OBSERVATIONS 



ON THE 



INCLINATION AND DECLINATION 



OF THE 



MAGNETIC NEEDLE. 



By LIEUTENANT COLONEL J. A. HODGSON, 



Surveyor General of India ; and 



MONSIEUR DE BLOSSVILLE, 



Honorary Member Asiatic Society. 



Communicated by Captain J.D.Herbert, Assistant to the Surveyor General. 



Th E progress which has latterly been made in the investigation of the 

 magnetic phenomena is remarkable. A new science, that of Electro- 

 magnetism, has been created, and the happy conjecture hazarded by 

 Playfair, that the mysterious properties or powers of matter, which we 

 name gravity, chemical affinity, galvanism, magnetism, electricity, &c. 

 would be one day referred to a single cause, has been almost realized. The 

 very striking facts developed in the thermo-electric experiments have 

 been ably investigated, while the law of the magnetic force has been 

 determined, and the effect of local attraction rigorously calculated. Tlie 



B 



