LANTERNS AND THEIR MANIPULATION 121
General experience, however, does not go in the direction
of any triple dissolver, but prefers an ordinary bi-unial dis¬
solving tap for a pair of the lanterns, and a separate four-way
tap (fig. 67) for the other one, which turns on or cuts off both
gases as required.
A very usual plan
is to have pieces
of brass tubing
pluggedat the top,
fixed up each
comer of the back
of the lantern, cut
where the top
lantern joins on,
but connectedwith
an inch or two of rubber so as to act as one. The supply-
tubes are stretched over the bottom ends of these pipes, and
small side nozzles level with the dissolving taps connect with
these. Rubber tubes connect the dissolving taps with the
jets as usual. This is decidedly the most popular plan ;
but some experienced exhibitors prefer for each lantern to
have its own single four-way tap, governing its own jet alone,
supplied from brass mains as in the preceding case. Each
tap has a double arm (that is, one extending on each side of
the plug), and the upper pair of arms are connected by a
brass rod on one side, and the lower pair by a rod on the other
ends. The rods pass through sockets with pinching screws
fixed on the arms, so as to work any given arm at pleasure,
or slide loose when the screw is slackened. The result is
that either the top pair or bottom pair of lanterns can be
dissolved together at pleasure, the third being left independent
for separate use. Or the pairs can be changed in a moment
from top to bottom pairs if required.
66. Bi-unial and Lantern Effects.—A bi-unial lantern is
necessary for many other effects than dissolving views, as