The Art of projection and complete magic lantern ... - Yesterday Image

together at one end, and a hole cut away to allow the tap of the86bag toprotrude, a flap is hinged about six inches from the top end to hold theweights and prevent them slipping, the boards are readily put togetherby anyone possessing the slightest idea of joinery.When Two Bags are used.— Boards slightly different are used,and are known as " double pressure boards," although practically one,but arrangement must be made to compensate for the second bag beingintroduced, if two bags were placed under the ordinary boardsintendedfor one, the space they would occupy would bring the top board upright,at right angles to the bottom, consequently it would not work or holdthe weights, to compensate for this, the front part of the boards mustbe raised about a foot (Fig. 42). A bottom case or frame is madeto which the regular board is hinged at the back, each side of this thereis a number of sliplike racks or slots, in which the raising struts fix,allowing the bags to be tilted angle to angle ; supposing this frontwas raised too high when the bags were nearly empty, the back of theboards would be very much lower than the front, and the weightswouldfall off ; to secure them, two flaps are made, both folding inwards, theweights are placed between these and are thus secured in position,when bags are full and when empty. Double boards to be free ofall risk should on no account ever have a flap between each bag,although it has been advised on former occasions in manuals on thelantern ; reasons why this should not be done is dealt with later on.But a canvas should be placed between the top and bottom bags,hole at the end for the strap to pass through.with aWhen the bags are full with weights adjusted they have a peculiar knackof slipping away out towards the back, to prevent this a good wide strapwith a buckle should be screwed to the boards, fastened round the backof the bags and through the hole in the canvas lining, thus strapping theminto position and so preventing any slipping back. If the opening in frontof the boards is not sufficiently large in the boards for the taps to comethrough it is very annoying, as the taps get out of reach as the bags godown, often causing a kink in the tubing. This hole should be cut awayat least 8 inches deep on top and bottom boards.Directions for Use.—Put the hydrogen bag at the bottom, andoxygen at the top, pull the centre sail cloth tight between them by theloop, while the lower board is flat on the frame; then strap them up andraise the boards into the position shown in the drawing by raising thehinged end, and the lower board will drop to its place of its own accord.