64 AKSEL S. STEEN. TERRESTRIAL MAGNETISM. [NORW. POL. EXP. 
vibrations and deflections, Dr. Neumayer also considered it necessary to 
introduce a new constant, «, 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 formule: 
From deflection observations, 
Cu 
sin p 
! — (88 -+4) | (4) 
From vibration observations, 
H = pp, [t+ 09 +t]. (5) 
The constant u, of which the form is 
w= Wing 1+ pe+ aorta S)I, (6) 
may of course be calculated, like the constant C, from the observations taken 
im 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, 
