This point evidently lies upon the branch _z_M of the evolute in Fig. 23.
The process of finding one upon the other branch _x_N is shown in the
lower part of the diagram, Fig. 25. The operations being exactly like
those above described, will be readily traced by the reader without
further explanation.
* * * * *
AUTOMATIC COMMUTATOR FOR INCANDESCENT LAMPS.
Incandescent electric lighting, already pushed to such a degree of
perfection in the details of construction and installation, continually
finds new exigencies that have to be satisfied. As it is more and more
firmly established, it has to provide for all the comforts of existence
by simple solutions of problems of the smaller class.
Take for example this case: Suppose a room, such as an office, lighted by
a single lamp. The filament breaks; the room becomes dark. The bell push
is not always within reach of the arm, and it is by haphazard that one
has to wander around in the dark. This is certainly an unpleasant
situation. The comfort we seek for in our houses is far from being
provided.
M. Clerc, the well known inventor of the sun lamp, has tried to overcome
troubles of this sort, and has attained a simple, elegant, and at the
same time cheap solution. The cut shows the arrangement. The apparatus is
connected at the points, BB', with the lighting circuit.
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