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Llectro-Magnetic Apparatus and Experiments. 265 
the mechanical. application of electro-magnetism has been turned 
to profitable account. This engine is to undergo considerable 
alteration and improvement, when a eens and eating of 
it will be published. 
That much remains yet to be atetaion! concerning the most 
ddveditayinad form and size of magnets and armatures, will appear 
from the following observations made during last October, while 
on a visit in Boston. 
First: it is possible to present a piece of soft iron to the most 
powerful magnet in such a manner that it will not be attracted 
in the least by the magnet. re 
Ei xperiment.—Drill a hole in the center of the pole of an elec- 
tro or permanent magnet, to admit a small sliding rod of brass. 
To one end of this sliding rod, fasten a small disc of soft iron. 
The diameter of the disc must be less than that of the pole of 
the magnet, and the thickness or axis of the disc, must be con- 
siderably less than its own diameter. Put the sliding rod in its 
place, and if the disc of soft iron be exactly parallel to the face 
- of the magnetic pole, if will not be attracted by it, be the magnet 
never so strong. If the disc isin ‘the least’ inclined from paral- 
lelism, it will be attracted by the magnet. The experiment will 
appear more satisfactory if varied in the followmg manner. Place 
the disc of soft iron, with its’sliding rod, in a frame, and place 
the magnet on a rest, so that its position can be varied; the same 
results will follow as before. Again: put the disc, without its 
silding rod, on the center of a large magnetic pole, and it will 
_ slip down to the edge of the pole, and there adhere. Again: 
sprinkle iron filings on a piece of paper laid over the end of a 
bar magnet ; the filings will cluster over the pole around a va- 
cant space at its center. Again: drill out the disc of iron so as 
to make a ring, whose width is greater than its thickness, and 
present it to the magnet in the same manner as the disc, and the 
ring will be attracted by the magnet. It appears from this, that 
the disc, though magnetized by induction is polarized in a radial 
direction, and the forces counteract, or disguise each other’s in- 
fluence upon the magnetic pole. When the diameter of the disc 
is greater than that of the magnetic pole, there cannot be this 
counterpoise of forces. When the disc is inclined to the face of 
the magnetic pole, it becomes polarized in the direction of an 
oblique line, joining that part of the disc in contact with the 
Vou. XXXV.—No. 2. 34 | 
