WEBER OX A TRANSPORTABLE MAGNETOMETER. 575 



1839, April 13. 

 IQl^ 31' 



In the open air. 

 18° 18' 0" 



In the magnetic observatory. 

 18°^ 23' 36" 



The mean influence of the 

 may therefore be taken as 



showing a difference of — 5' 36". 

 copper case in this iiistrument 

 = -5'. 



Observation of the Variations of Declination. 



On the 15th April 1839, from b"^ 25"" to 7^ 27m-5, the varia- 

 tions of declination were observed alternately, with the mag- 

 netometer in the Gottingen Observatory, and with the small 

 magnetometer. In the following table the four first columns 

 show the immediate results of observation with the two appa- 

 ratus. In the final column the observations with the small 

 magnetometer are reduced according to the proportion of the 

 value of the scale divisions. The two series of observations are 

 exhibited graphically in fig. 5, for the purpose of comparison. 

 It may be seen from this example that the obsen'ations of the 

 variations of declination can be made with a portable mag- 

 netometer with much accuracy. 



