254 
PROFESSOR TYNDALL’S FURTHER RESEARCHES 
By changing the position of the tubes within the helices, the magnets could be 
driven violently through the field of view, or could be held rigidly against the respect- 
ive helices. As in all other cases, the centre of the cylinders were neutral points, 
and the two ends of each were poles of opposite qualities. The polarity was of course 
the same as that of iron. 
A small quantity of iron filings were kneaded thoroughly in wax, and a cylinder 
formed from the mass. Its deportment was also very violent, and its polarity was of 
course just as clear and pronounced as that of a solid cylinder of iron could possibly be. 
Sulphate of iron w’as next examined: the crystallized substance was enclosed in 
two glass tubes and tested in the usual manner. 
XXII. 
Cylinders of Sulphate of Iron, 
length 4'5 inches, 
diameter 0'7- 
Current direct. 
Position 1. 510 
Position 2. 600 
Position 3. 700 
Current reversed. 
510 
370 
220 
The red ferroprussiate of potassa is a magnetic salt ; 
ing results were obtained : — 
XXIII. 
with this substance the follow 
Cylinders of red Ferroprussiate of Potassa. 
length 4'5 inches, 
diameter 0'65. 
Current direct. 
Current reversed. 
Position 1. 
610 
250 
Position 2. 
630 
220 
Position 3. 
655 
197 
In this case also the crystallized salt was enclosed in glass tubes. 
Two glass tubes were next filled with carbonate of iron in the state of powder : the 
following are the results : — 
XXIV. 
Cylinders of Carbonate of Iron. 
length 4 inches, 
diameter 0'5. 
Current direct. 
Position 1. 185 
Position 2. 620 
Position 3. 740 
