574 -WEBER OX A TRANSPORTABLE MAGNETOMETER. 



2. Azimuthal determination of the Magnetic Axis. 

 In order to reduce the observations to the same time, the 

 decUnation -was observed simultaneously in the magnetic ob- 

 servatory. 



Before "1 



reversal J 



After ) 



reversal / 



Time. 



1859, 



April 11. 



11 



11 37-5 



Azimuth 



of the 



CoUimation 



Line. 



131 22 43 



132 2 59 



Observation 



in the 



Magnetic 



Observatory. 



o / // 



18 26 26 



18 29 9 



Reduced 

 Azimuth. 



131 20 



132 2 59 



Azimuth 



of the 



jVIagneiic Axis. 



131 41 29-5 



3. Azimuthal determination of the true North. 



Three visible objects were observed, the positions of which, 

 in respect to the Gottingen Observatory, ai'e given by geode- 

 sical measurements. 



As there is no con-ection to be applied on account of torsion, 

 we obtain immediately from hence the ivester/y declination, by 

 deducting the azimuth of the magnetic axis from the azimuth 

 of the tiiie north. 



150° 6' 14"- 131° 41' 29"-5 = 18° 24' 44"-5. 



This result corresponds to \l^ 37"-5, 11th April 1839. The 



declination observed at the same time in the magnetic observa- 



torv was 



18° 29' 9", 



showing a difference of — 4' 24"-5, which probably is only in 

 part due to error of observation, and is in part caused by the 

 influence of the copper case surrounding the magnetometer, 

 which may not be wholly free from iron. Repeated measure- 

 ments, and compai-isons with the observations in the magnetic 

 observatoiy, may serve to deduce such an influence if it exists, 

 so that it may be taken into account in future measurements. 

 A second measurement actually gave a similar result, namely. 



