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