It is the
thunder-storm. Mother Earth is the great depository of the fluid. The
heavy clouds, as they gather, are likewise full. Across the space that
lies between the exchange takes place--the lightning-flash.
In the preceding chapter I have hastily alluded to the phenomenon known
as the key to electricity as a utilitarian science; a means of material
usefulness. These uses are all made possible under the laws of what we
term INDUCTION. To comprehend this remarkable feature of electric
action, it must first be understood that all electrical phenomena occur
in what has been termed an "_Electrical Field_" This field may be
illustrated simply. A wire through which a current is passing _is
always surrounded by a region of attractive force_. It is
scientifically imagined to exist in the form of rings around the wire.
In this field lie what are termed "lines of force." The law as stated is
that the lines in which the magnetism produced by electricity acts
_are always at right angles with the direction in which the current is
passing_. Let us put this in ordinary phrase, and say that in a wire
through which a current is passing there is a magnetic attraction, and
that the "pull" is always _straight toward the wire_.
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