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



vibrations and deflections, Dr. NEUMAYER also considered it necessary to 

 introduce a new constant, /u, which is proportional to the magnetic moment 

 of the magnet in question, and by the aid of which the absolute horizontal 

 intensity may be deduced from deflection observations alone, or from vibration 

 observations alone, according to the following formulae: 

 From deflection observations, 



sin <p 

 From vibration observations, 



The constant (i, of which the form is 



(6) 



may of course be calculated, like the constant C, from the observations taken 

 in Hamburg and Wilhelmshaven. 



THE MAKING OF THE OBSERVATIONS. 

 OBSERVATIONS OF DEFLECTION. 



The brass rod intended for the deflection-observations, was divided into 

 two parts to facilitate transport, one half being affixed to each side of the 

 alhidade of the horizontal circle. On each half of the rod, at definite 

 distances from the centre of the horizontal circle, are placed two low uprights, 

 between which a carriage may be inserted for the support of one of the 

 magnets V and VI as deflector. The carriage may be screwed to the rod. 

 Above the deflector is placed a box in which there is a thermometer. The 

 arrangement of the rod only permits of deflections with the deflector placed 

 E and W, not N and S. 



Not only was the small needle used as deflected magnet, being specially 

 intended for this, but also the double needle, when, as frequently happened, 

 the mirror of the small needle gave a rather indistinct reflection. 



