say, the intensity of the electric field at any place along the line
AB in Fig. 191 is represented by the ordinate y of an inclined
straight line CD. Such an electric field is called a tapering



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ELECTRIC OSCILLATIONS AND ELECTRIC WAVES. 249

field for the sake of brevity. Imagine the ether cells in Fig. 189
to be displaced in a manner to represent the tapering electric
field of Fig. 191. Then the two positive cells to the left of the
middle cell in Fig. 190 are displaced downwards more than the
two positive cells to the right of the middle cell in Fig. 190, so
that the two torques a and b exceed the two torques c and d,
that is, the middle cell is acted upon by an unbalanced torque,
and, therefore, the middle cell must be gaining angular velocity
about an axis perpendicular to the plane of the paper. What is
here said of this particular cell is true of all the ether cells in
Fig. 189 in the case of a tapering electric field; therefore, a
tapering electric fiM produces a continuously increasing magnetic
,fiM at right angles to itself,*

131. Electric action of a tapering magnetic field. — ^Hereafter
a chain of geared cells which is free irom distortion will be
thought of as standing in a straight row as shown in Fig. 192a,

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a h

Fig. 192a.
