186 



ed. The correction, for loss of magnetism by the needles, was 

 ascertained from observations at Philadelphia, London, and Paris, 

 and curves traced representing the loss, from which the specific cor- 

 rection, to be applied at any epoch, was readily obtained. The curve 

 for one of the needles, showed a tendency towards a permanent 

 state, and for the other was nearly a straight line. Irregular changes 

 took place in neither needle. The author's experience with these 

 needles, induces him to give a preference to the method of placing the 

 needles in pairs, over that which he has hitherto employed, of keeping 

 each needle separate from the other. A suggestion also results in 

 the use of the dipping needle, of the necessity of ascertaining that the 

 needles have, in the reversal of the poles, been charged nearly, or 

 quite, to saturation. The author takes occasion to correct his state- 

 ment in regard to the inefficacy of heating needles in boiling water 

 in producing an approach to a permanent magnetic state. The ob- 

 servations at each station, with the corrections employed, are given 

 in tables; and the number observed for the dip, or calculated for the 

 horizontal or total intensities, are compared with the results of other 

 observers. 



The Memoir concludes with the following Abstract of the numeri- 

 cal results. 









Long. 













No. 



P.aces. 



Latitude. 



from 

 Paris. 





Date. 



Horizontal 

 Intensity. 



Dip. 



Total 



Intensity. 







O ' 



o ' 







Paris =1 



o ' 



Paris =1 



1 



Edinburgh 



55 57 N. 



5 32W. 



Feb. 



3, 1837 



0.841 



— — * 







2 



Dublin - - 



53 23 „ 



8 4l„ 



Nov. 



20, 1836 



0.879 



* 







3 



London - 



51 31 „ 



2 26 „ 



June 



16, 1837 



0.939 1 



69 16.0 



1.021 



4 



Brussels 



50 51 „ 



2 02E. 



July 



25, 1838 



0.969 



■* 







5 



Berlin 



52 32 „ 



11 02 „ 



Dec. 



16, 1837 



0.979 



68 08.5 



1.014 



6 



Paris 



48 50 „ 



00 „ 



Aug. 



17, 1837 



1.000 



67 20.8 



1.000 



7 



Vienna - 



48 13 „ 



14 02 ., 



March 23, 1838 



1.090 



64 49.7 



0.989 



8 



The Flegiere 







' 



Aug. 



26, 1837 



1.099 



64 35.8 



0.987 



9 



Brientz - 











Sept. 



<£L, ,, 



1.078 



65 06.7 



0.987 



10 



The Faulhorn 











Sept. 



20, „ 



1.082 



65 01.7 



0.987 



11 



Geneva - 



46 12 „ 



3 49,, 



Aug. 



25, „ 



1.086 



64 49.8 



0.984 



12 



Chamberi 









June 



21, 1838 



1.089 



64 35.0 



0.979 



13 



Chamouni 











Aug. 



26,1837 



1.088 



64 38.2 



0.979 



14 



Lyons 



45 46 „ 



2 29 „ 



June 



25, 1838 



1.078 



64 49.0 



0.978 



15 



Milan - - 



45 28 „ 



6 51 „ 



June 



10, „ 



1.111 



63 54.7 



0.972 



16 



Venice 



45 26 „ 



10 10,, 



April 



H, „ 



1.129 



63 21.9 



0.971 



17 



Trieste 



45 38 „ 



11 27 „ 



April 



4, „ 



1.128 



63 20.5 



0.970 



18 



Florence 



43 47 „ 



8 55„ 



May 



28, ii 



1.170 



62 05.5 



0.965 



19 



Turin - - 



45 04 „ 



5 20 „ 



June 



17, „ 



1.094 



63 52.2 



0.959 



20 



Rome 



41 54 „ 



10 10 „ 



May 



18, ,, 



1.225 



60 14.0 



0.952 



21 



Naples 



40 52 „ 



11 57 „ 



May 



7, „ 



1.249 



59 05.1 



0.938 



* Dip not observed. 



t Mean of results in June, July and Aug. 1837, and in July and Aug. 1833. 



