18 
PROFESSOR TYNDALL ON THE DIAMAGNETIC FORCE, ETC. 
tangents of the deflections observed in each case : neglecting the indices, the figures 
in the second column express the number of oscillations accomplished in a minute, 
multiplied by a constant factor to facilitate comparison : the forces operating upon 
the bars being proportional to the squares of the number of oscillations, the simple 
addition of the index figure completes the expression of these forces. 
In these experiments the bismuth bar set across the lines of magnetic force, while 
the bar of iron set along them ; the former was so cut from the crystalline mass, that 
the plane of principal cleavage was parallel to the length of the bar, and in the expe- 
riments hung vertical. I thought it interesting to examine the deportment of a bar 
of bismuth which should occupy the same position, with regard to the lines of force, 
as the bar of iron ; that is to say, which should set its length axial. Such a bar is 
obtained when the planes of principal cleavage are transverse to the length. 
Table V. 
Bar of bismuth. No. 2. 
length 0‘8 of an inch, 
width 0T3 of an inch, 
depth O' 15 of an inch. 
Set axial hetiveen the excited poles. 
Strength of current. 
Repulsion 
68 
67" 
182 
187" 
218 
218" 
248 
249" 
274 
273 " 
315 
309" 
364 
350" 
401 
366" 
A deportment exactly similar to that exhibited in the foregoing cases is observed 
here also : up to about 280 the repulsions are accurately proportional to the squares 
of the current strengths, and from this point forward they increase in a less ratio. 
A paramagnetic substance was next examined which set its length at right angles 
to the lines of magnetic force: the substance was carbonate of iron. The native 
crystallized mineral was reduced to powder in a mortar, and the powder was com- 
pressed. It was suspended, like the bismuth, between the flat poles, with its line of 
compression horizontal. When these poles were excited the compressed bar set the 
line of pressure from pole to pole, and consequently its length equatorial. 
