ita enti 
a I ET ED 
AND INSTRUMENTS AT MUNICH. 52) 
very regularly turned glass or metal ring, the moment of which, 
even if the mass should not be homogeneous, may be determined 
with all requisite exactness by a method which I will give at 
a future opportunity. Having obtained the moment of inertia 
in the manner referred to, the ring is placed on the magnet, and 
the time of vibration determined afresh with the moment of inertia 
thus augmented. We have then the equation 
2 
peg eosnl aa) 
where R denotes the moment of inertia of the ring, and T’ the 
time of vibration with the ring. This equation, combined with 
the preceding, gives the value of K *. 
I subjoin some single measurements of each kind taken from 
our magnetic journal, in order to show the accuracy practically 
attainable. 
MaGnet V. 
Observed time of passing the wire t. 
Intensity... * : 39°5 
_ * [Ina notice inserted in the Annalen fiir Meteorologie und Erdmagnetismus 
for 1842, Dr. Lamont remarks, that “‘ measurements of the absolute intensity 
always comprehend two operations, i.e. of vibration and of deflection; in the 
experiments of vibration the bar is in the magnetic meridian, but in those of 
deflection it forms an angle with the magnetic meridian, which is in all cases 
rather considerable. Up to the present time it has been assumed that the mag- 
netic force of the bar continues the same in these two positions, which will not 
however be the case if the induction caused by the earth’s magnetism be of 
sensible amount.” From experiments which Dr. Lamont has made, he infers— 
Ist, that in all magnets the induction is so considerable, that it must be taken 
into account in measurements of the absolute intensity ; and, 2nd, that more 
magnetism is induced in large magnets than in small ones, more in thick than 
in thin magnets, and more in bars which are less hard than in those which are 
completely hardened.—E. S.] 
+ When the time of vibration is small the passages of the needle succeed 
each other too rapidly for all to be observed ; the most convenient mode is to 
observe every third passage, which has been done in these observations. 
VOL. III. PART XI. 2m 
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