5, and sprinkle filings over the surface.
They will, when the glass is gently tapped, arrange themselves in
concentric circles, the smallest and innermost being the best defined
because the magnetic force is strongest there. Fig 6 is an actual
reproduction of the circular lines produced in this fashion by iron
filings in the field of force surrounding an electric current.
[Footnote 1: It will not be out of place here to recall Ampere's
ingenious rule for remembering the direction in which a current urges
the pole of a magnetic needle. "Suppose a man swimming in the wire with
the current, and that he turns so as to face the needle, then the north
pole of the needle will be deflected toward his left hand."]
[Illustration: Fig. 4]
This experimental evidence must suffice to establish two of the three
fundamental points stated at the outset, for they prove conclusively
that the electric current may be treated as a magnetic phenomenon, and
that both in the case of the pole of a magnet, and in that of the wire
which carries a current, a portion, at any rate, of the energy of the
magnetic forces exists outside the magnet or the current, and must be
sought in the surrounding space.
Pages:
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82