VARIATIONS OF THE MAGNETIC INTENSITY. 319 



may have sustained, by comparing its rate of vibration at Paris 

 on his return, vi'ith its rate at a station in Peru, in the line of 

 no dip, in which comparison he has assumed the relation of the 

 force at that station to the force at Paris to be as 1 to 1-3482. 

 The loss of magnetism sustained by the needle on this estima- 

 tion was altogether inconsiderable. The times of vibration at 

 four other stations at which this needle was employed, cor- 

 rected for temperature and arc, give the following values of 

 the total intensity. 



Payta 5° 6'S. . 



OfFak 2 , 



Port Jackson .. 33 52 

 Isle of France . . 29 9 



These determinations are inserted in a map engraved in 1832, 

 referred to in a paper read by M. Duperrey to the Academy 

 of Sciences at Paris in 1833, entitled, " Considerations sur le 

 Magnetisme Terrestre." Captain Duperrey notices, that at two 

 other stations, viz. Talcahuano and St. Catherine's, he observed 

 the times of vibration of a dipping needle, the poles of which 

 were reversed at each station, in the usual manner, for the ob- 

 servation of the dip ; and that the results derived from the vi- 

 bration of this needle, presuming it to have received, on every 

 occasion when the poles were changed, an equal magnetic 

 charge, correspond in a remarkable manner — as indeed they 

 do, — with the subsequent observations of Captains King and 

 Lutke ; but Captain Duperrey, of course, attaches to these 

 determinations no independent value, and therefore I need not 

 notice them further. Captain Duperrey has also communicated 

 to me three results obtained at stations in France in 1834, with 

 one of M. Hansteen's needles, made, as it appears, with very 

 great care, and with every necessary jirecaution. These re- 

 sults are, for 



Lat. Long. W. Paris. 



Brest 48-24 .. 6-50 ., 1-365 



Landevence . . 48-18 . . 6'o5 . . 1-363 

 Orleans 47-54 .. 0-26 .. 1-.341 



I may take this opportunity also of adverting to the observa- 

 tions of Professor Bache and other gentlemen of the United 

 States, which were not included in my report. These obser- 

 vations were made at New York, and in the adjoining states ; 

 and Mr. Bache is now engaged in connecting them with Eu- 

 rope, and, consequently, with the general body of the intensity 

 observations. Until this comparison is complete, which it will 

 not be until Mr. Bache returns to the United States, the ob- 



