92 



OBSERVATIONS OF THE MAGNETIC INTENSITY 



At Rome the chronometer was compared, before and after the observations, 

 with the observatory clock of the Roman College, and, at Naples, with that of 

 the Royal Observatory. 



The horizontal intensity observed at Paris, for 1838, is taken as unity in the 

 calculations, the correction for loss of force in the needles being applied for the 

 same epoch. The dip which is used in calculating the total intensity is a mean 

 of that actually observed at Paris in 1838, and of that which would result from 

 applying the yearly diminution of 2'.8 to the dip observed in 1837. 



Observations at Rome and Naples. 



For Horizontal 



Intensity. 









Place. 



Needle. 



Date. 



Temp. 



No. 



of 



Series. 



No. of 

 Oscill'ns. 



Time of 



Ten 

 Oscill'ns. 



at 60°. 



Sees. 



Coeffic't 



of 



Correction 



for 



Loss of 



Magnet'm. 



Horizontal 



Intensity. 



Year. 



Month. 



D. 



H. 



Fah. " 



Paris 1. 



Rome* 

 Romet 



Cylinder 

 Bar 



Cylinder§ 



1838 



u 

 li 



May 



18 



H, A. M. 

 P.M. 



67.3 

 67.0 

 65.0 

 66.2 



2 

 2 

 1 

 1 



650 

 600 

 350 

 350 



31.574 

 34.122 

 31.539 

 31.777 



0.9935 

 0.9981 

 0.9935 



Mean, 



1.223 

 1.226 

 1.226 



Rejected. 



1.225 



Naples^ 



Cylinder 

 Bar 



1838 



May 



7 



8, A. M. 



Ill " 



76.2 

 75.2 



2 

 1 



700 

 350 



31.290 

 33.674 



0.9921 

 0.9977 



Mean, 



1.244 



1.258 



1.249 



For Dip 



• 











Rome,|| 1838, May 15, Needle No. 1, 60° 13'. 1 

 18, " No. 2, " 14.9 





Mean, 6( 



)° 14'. 0. 







Naples,1I 1838, May 7, Needle No. 1, 59° 04'.8 



No. 2, " 05 .5 





Mean, 59 



° 05'. 1. 







Total Intensity at Rome, compared 

 " " Naples, " 



with P 



6t 



aris as ui 



lity, 0.95 

 " 0.93 



25. 



80. 





In taking the means for the horizontal intensity, weight is allowed in pro- 

 portion to the number of oscillations observed. 



The observations at Rome confirm the statement of M. Quetelet, that no 

 effect is produced upon the needle by the volcanic tufa. 



* Monte Mario. 



§ In niche, on stone. 



t Temple of Venus and Rome. 

 II Monte Mario. 



I Aversa. 

 IT Aversa. 



