254 M. Duperrey's Observations 



Art. XVII. — Magnetical Observations on the Variation and 

 Dip of the Needle, made during the Voyage of the Coquille 

 from Toulon to Port Jaclcson, in 1822, 3, and 4. By M. 

 Duperrey, Commander of the Expedition. Communicated 

 by Sir Thomas Makdougall Brisbane, K. C. B. F. R. S. 

 London and Edinburgh. 



When M. Duperrey, the distinguished commander of the 

 Coquille, which performed the last voyage of discovery fitted 

 out by the French government, visited Port Jackson on his 

 return home, he communicated to Sir Thomas Brisbane, 

 Governor of New South Wales, the complete series of his 

 magnetical observations. In order to promote the interests 

 of science, Sir Thomas has kindly given us the use of this 

 MS. for the purpose of publishing an abstract of its leading 

 results. 



The scientific reader will not fail to observe the great im- 

 portance of these observations, in reference to the determina- 

 tion of the form of the magnetic curves, and of the position of 

 the magnetic equator, and the magnetic poles of the earth. 



The two dipping compasses employed by M. Duperrey 

 were the same which were used by Captain Freycinet on board 

 the Uranie. One of these was intended to be used only on shore, 

 while the other, which was mounted with a double suspension, 

 was particularly destined for being used at sea. The first of 

 these compasses had four needles, and the second two, and 

 wherever they were observed, either at land or at sea, their 

 poles were changed by twenty frictions given upon each of their 

 faces by means of strongly magnetised bars. The recorded in- 

 clination or dip of the needle is the mean of the observed in- 

 clinations taken before and after the change of poles. 



In order to understand the following tables, it may be remark- 

 ed that the north point of the needle is the one which is di- 

 rected freely to the pole of the same denomination. 



The inclinations which have no sign, indicate that the north 

 point of the needle is below the horizontal line, so that the 

 observation is made to the north of the magnetic equator ; 

 while those that have the sign — indicate that the north point 



