248 
PROFESSOR TYNDALL’S FURTHER RESEARCHES 
Thus in passing from position 1 to 3, or vice versa, a permanent deflection corre- 
sponding to four divisions of the scale was produced. By raising or lowering the 
respective prisms at the proper moments the amplitude of the oscillations could be 
considerably augmented, and, when at a maximum, could be speedily extinguished 
by reversing the motions of the prisms. In six different series of experiments made 
with this substance the same invariable result was obtained. It will be observed that 
the deflections are in all cases in the same direction as those produced by bismuth 
under the same circumstances. 
The following results were afterwards obtained with the same prisms in the pre- 
sence of M. De la Rive ; the current was “direct.” 
VIII. 
Position 1. 652 
Position 2. 650 
Position 3. 648 
On the negative result arrived at with this substance, it will be remembered that 
M. V. Feilitzsch bases one of his arguments against the conclusions of M. Weber. 
Calcareous spar was next submitted to experiment. Two cylinders of the trans- 
parent crystal were prepared and examined in the manner already described. The 
results are as follows : — 
IX. 
Cylinders of Calcareous Spar. 
length 3 inches. 
diameter 0’7. 
Current direct. 
Position 1. 6995. 
Position 2. 698'5. 
Position 3. 697’5. 
Here, as in the other cases, the deflection was permanent, and could be augmented 
by the suitable raising or lowering of the respective cylinders. The action is small, 
but perfectly certain. The magnet was steady and moved promptly and invariably 
in the directions indicated by the numbers. It will be observed that the deflections 
are the same in kind as those produced by bismuth. 
The intrusion of other employments compelled me to postpone the continuation of 
these experiments for several weeks. On taking up the subject again, my first care 
was to assure myself that the instrument retained its sensibility. Since the experi- 
ments last recorded it had been transported over several hundred miles of railway, 
and hence the possibility of a disturbance of its power. The following experiments, 
