70 



AKSEL S. STEEN. TERRESTRIAL MAGNETISM. [NORW. POL. EXP. 



All these determinations of /u and C refer to cases in which the small needle 

 has been used as deflected magnet, and may therefore be directly compared. 



It will be seen from the two tables that in the case of magnet V, the 

 values found for /.i, which is proportional to the magnetic moment of the 

 deflector, exhibit such slight differences, that the moment of this magnet 

 may be assumed to have remained unchanged throughout the expedition. 

 On the other hand, it appears as if the moment of magnet VI has undergone 

 a weakening, which cannot be left altogether out of consideration. On Sep- 

 tember 30th, 1893, Capt. SCOTT-HANSEN makes the following remark in his 

 magnetic journal: "Inadvertently allowed a steel knife to come near magnet VI'. 

 This may perhaps explain the above-mentioned weakening of the moment of 

 the magnet, and in the absence of other particulars, there may be reason 

 to suppose that as regards magnet FJalso, p has remained constant in each 

 of the two periods marked by the above-mentioned contact, and that thus 

 the value found in Hamburg in 1893 may be considered as applicable for 

 the time before the 30th September, 1893, and the value found in Wilhelms- 

 haven in 1897, for the time after the 30th September, 1893. 



As both fi and C, as formulae (6) and (2) show, are determined 

 separately by a combination of the time of vibration and the angle of 

 deflection, and the double needle was also used during the expedition as 

 deflected magnet for the determination of the angle of deflection, the value 

 of the two constants in question must be known in this case also. With 

 this object, a series of deflection observations were taken in Wilhelms- 

 haven, with the double needle both in position P t and in position P a as 

 deflected magnet. If p and C are calculated by these observations combined 

 with the corresponding determinations of the magnets' time of vibration, the 

 following values are obtained: 



