210 A. M. Mayer— Researches in Hlectro-Magnetism. 
inch in diameter ; and being magnetized again in the helix with 
the same strength of current, the bundle caused a far greater 
deflection in the needle than when it acted without the central 
wooden cylinder. I consider this experiment as very conclu- 
sive of the surface action of magnetism, for in the two measures 
we used one and the same mass of metal, subjected to exactly 
the same magnetizing influence, and only differi ring in the extent 
of exterior surfaces existing during the two experiments. That 
the increase of force with the surface was not owing to a change 
of distance of the wires from the interior surface of the helix is 
conclusively shown in the next section 
But there are differences to be made between these analogous 
phenomena of frictional electricity and of magnetism; in mag- 
netism a considerable thickness of metal is required to ’ develope 
this action at the BUrEACE ; so that (Ex. ek a tube must have a 
x 
a tube, while no similar nation. a be obtained with frictional 
electricity. 
Experimen ts to determine whether a change of positon of a bar in 
the interior of a helix causes a change in the intensity of rts magnet- 
ization.—Theory indicates that no change in the degree of mag- 
netization will follow a change of position of a bar in the inte- 
rior of a helix, and the following experiments conclusively 
prove the truth ‘of this deduction 
Ex. 81. In the interior of helix E resting on the bottom of 
the opening was placed a cylinder of soft iron ‘83 inch diam. 
and 9 ins. long. posed to this helix was helix W, (in the 
same circuit) with the 400 wire-core. Needle was brought to 
such a eg that it stood at 0° when the circuit was open or 
close 
Ex. 
ratus what difference, if me existed sa Betche the netizing 
effects of a helix whose turns were inclined in the successive 
layers alternately in opposite and equal angles with the axis, 
