with the magnet, A, being suddenly detached by this movement of the
lever, N, the induced current which is then produced causes the
display, near the pump, of a disk, Q, upon which is inscribed the word
"Full." This is a signal to stop pumping.

* * * * *




THE TELEPHONIC HALLS OF THE ELECTRICAL EXHIBITION.


Telephonic communication between the Opera and the Exhibition of
Electricity is obtained by means of twenty conducting wires, which are
divided between two halls hung with carpets to deaden external noises.
We represent in the accompanying engraving one of these halls, and the
one which is lighted by the Lane-Fox system of lamps. As may be seen,
there are affixed against the hangings, all around the room, long
mahogany boards, to which are fastened about twenty small tablets
provided with hooks, from which are suspended the telephones. The
latter are connected with the underground conductors by extensible
wires which project from the wooden wainscot of which we have just
spoken, so that it is very easy for the auditors to put the telephones
to their ears.

[Illustration: ONE OF THE TELEPHONIC HALLS AT THE ELECTRICAL
EXHIBITION.]

As the telephones are connected in series of eight with the same