Ehdro-Magitetic EcopermtCnU made by 
ed no mjtgnetism ; but when taken asunder, both halves tvere 
found magnetic, each having an opposite pole to the other. Gn 
joinrog them again, all magnetism disappeared, but oh sepa- 
rating them, it shewed itself again, 
5. We took a steel-disk, Fig. 5^., of about one inch in dia- 
meter, perforated in its centre, in which was placed a gMss-tubO, 
containing the wire through which the electric-battery ^as re- ^ 
peatedly discharged. AB is the steel circular disk ; and CD the 
hole in its centre, through which is stuck the glass-tube, EF. 
The strongest discharges could not make this disk show any 
magnetism ; but when it was cut with a chisel in the direction of 
any of its diameters, for instance GH, both halves became mag- 
netic, each having a pole opposite to the other. Thus, GAH 
was the north, and HBG the south pole. When again joined 
together, no polarity appeared. 
6. As it might be suspected that the cutting of the disk with 
the chisel made it magnetic, another disk was cut through, with- 
out passing the electric discharge along its axis. It was not, 
however, found to be magnetic. 
7. Over a slip of brass ABCD, Fig. 6., was laid a glass-plate 
KLHI. Over the glass, the communicating- wire EF of the 
electric-battery went across. In the brass was a small hole G ; 
and in this a steel-needle, not magnetic, was stuck perpendicular- 
ly. After passing the discharge through EF, it became strong- 
ly magnetic. 
8. 1 shall now proceed to describe two very convenient electro- 
magnetic apparatuses, made by my iugenious friend M. Van den 
Boss. They are intended to show magnetism to be communi- 
cated to wires through which a galvanic ciirrent is circulating. 
ABCD, Fig. 7. is a copper, and EFGH a zinc, square plate, of 
about three centimeters side, kept from touching each other by 
the interposition of some small piece of wood LM. Both plates 
are attached and suspended to slender brass-wires, OF and' RS. 
The wire OF enters at P, in the hollow space formed by a case 
of very thin quills inserted together, and two decimeters long. 
The end of the wire comes out of the quill at the end T, and 
returns, being wound as a spiral round it externally to the other 
end. V, where it again enters the quill, and proceeds by a right 
line to S, where coming out, it descends, and is atlaclicd to the 
