A. M. Mayer—Researches in Electro-Magnetism. 209 
stated by that philosopher. “A copper wire, of the size usually 
employed for ringing door bells, passed through the axis of an 
iron tube, or a piece of gas pipe, about three feet long. The 
middle of this wire was surrounded with silk, and coiled into a 
magnetizing spiral, into which a large sewing needle was insert- 
ed. The wire was supported in the middle of the tube by pass- 
ing it through a cork at each end, covered with tin-foil, so as to 
form a good metallic connection between the copper and the 
iron. On the outside of the tube and opposite each other were 
placed two other magnetizing spirals, their ends soldered to the 
iron. When these two spirals were also furnished with needles, 
and a discharge from a Leyden jar sent through the apparatus, 
as if to pass along the wire, the needle inside of the 1ron tube 
was found to exhibit no signs of magnetism, while those on the 
outside presented strong polarity. This result conclusively 
shows that, notwithstanding the interior copper wire of this com- 
ound conductor was composed of a material which offered less 
resistance to the passage of the charge than the iron of which 
the outer portion was formed, yet when it arrived at the tin-foil 
covering of the cork, it diverged to the surface of the tube, and 
still further diverged into the iron wire forming the outer spi- 
rals. We must not conclude, however, from this experiment, 
that the electricity actually passes on the outside of the tube. 
On the contrary, we must infer from the following fact, that it 
passes just within the surface. If the iron be coated with a 
thin coating of sealing wax, the latter will not be disturbed 
Barlow and Harris have made experiments which show that 
magnetism is also a surface action; and in Exp. 11 of this pa- 
e we saw that when the surface of a wire-core was diminished 
y compressing the bundle the magnetism diminished with it. 
To show that this diminution of force was not, in major part, 
owing to the increased repulsion produced between the bars 
when brought nearer together, the following experiments were 
made. 
Fx. 30. About 200 3; inch wires were pressed together as 
tightly as could be by binding them in a bundle with silken 
cord, and the deflection they caused in the needle, when mag- 
netized in the helix, was noted ; they were now taken apart and 
bound as tightly as before around a wooden cylinder about 1 
