82 



OBSEKVATIONS OF THE MAGNETIC INTENSITY 



intended to return a second time, and which, therefore, afforded the means of 

 ascertaining the loss of magnetism of the needles. The number of needles em- 

 ployed, and of observations made, may, perhaps, farther entitle these results to be 

 allowed some weight in the determination of the relative intensity of magnetism 

 at these two important European stations. The instrument for measuring the 

 horizontal intensity was put in excellent order by Robinson, who also furnished 

 the dipping circle and needles. Besides the horizontal needles which I ordi- 

 narily used, I employed two others, and also observed by the statical method 

 of Professor Lloyd. The observations were made in the summer of .1837, and 

 again in 1838, the intervals between the respective series at London and Paris 

 being quite short. The place of observation at London was near Captain Ross' 

 former residence, at Westbourne Green, and at Paris, in the garden of the 

 observatory in the Magnetic Cabinet of M. Arago. The chronometer was 

 compared, before and after the observations, with the clock of the observatory 

 at Paris, and with the standard of Messrs. Arnold and Dent, at London. 



Observations for Horizontal Intefisity at London and Paris. 



Place. 



Needle. 



Date. 



Temp. 



No. of 

 OsciU'ns. 



Time of 



Ten 

 OsciU'ns. 



Corrected 

 Time of 



Ten 

 OsciU'ns. 



Mean. 



Coeffic't 



of 

 Corr'n 



for 

 Loss of 

 Magn'm. 



Horizontal 

 Intensity. 



Year. 



Month. 



D. 



H. 



M. 



Fah. ° 



Sees. 



Sees. 



Sees. 



Paris 1. 



Lond. 1. 



London 



Cylinder 



1837 



(1 



June 



24 



12 



06, P.M. 

 30, 



71 



761 



242 



280 



35.31 

 .29 



35,369 

 .349 



35.359 





1.069 



1.000 



Bar 







(( 

 (( 



2 

 3 



49, 

 10, 



73§ 



300 



ti 



38.704 



38.742 



38.742 





1.066 



1.000 



H. R. 







(< 



(C 



1 



2 



36, 

 01, 



77 



350 



'1 



31.23 

 .29 



31.275 

 .335 



31.305 





1.066 



1.000 



H. B't. 



4( 







16 



3 



4 



42, 

 01, 



72^ 

 72 



350 

 400 



25.01 

 .01 



25.029 



ii 



25.029 





1.062 



1.000 



Paris 



Cylinder 





Aug. 



4 



ii 



10 

 11 



58, A.M. 

 23, 



69 



300 



34.12 

 .13 



11 

 11 



34.286 



.9958 



1.000 



0.936 





Bar 





Li 





12 



1 



42, P. M. 

 02, 



701 

 70 



300 



37.42 

 .40 



11 

 11 



37.560 



.9980 



1.000 



0.938 





H. R. 





July 



13 



12 



04, 

 34, 



701 



350 



(1 



30.18 

 .16 



30.305 

 .325 



30.315 





1.000 



0.938 





H. B't. 



(1 



11 (( 

 (1 <i 



It 



10 

 11 



53, A.M. 

 10, 



70 

 69^ 



400 



24.19 



24.286 



11 



24.286 





1.000 



0.942 



