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

87On no account use two separate boards, although safe enough when usedprivately ; a public audience, we consider, should never be exposed to theslightest risk ; avoid ever using a double board with flaps between the bags,it is most risky, and after all has no practical issue, as the gas is consumedso the bags and flap gradually go down, and it is the easiest thingpossible in the dark for any one of the audience to push a form or chair,in their ignorance, against the bags, and if the flap should rest on anyobstacle of this kind the pressure is taken off the bottom bag, as it wasonce to the writer's knowledge.If this should happen the experienced operator would soon know thatsomething was wrong as the light would go down, and to keep it up toany degree of brightness he would have to continually reduce his oxygen,and knowing that the bags contained plenty of gas, would at once cometo the conclusion that something was amiss, and shut off thelantern foran interval. If this was allowed to continue the gas from the top bagwould pass into the bottom by way of the jet.Mr. Maiden's new boards have been made to his own idea for obtaininga greater pressure near the close of the lecture, without the addition ofan extra weight, this is brought about by making the top flap of theboards considerably longer than the other portions.WEIGHTS.The weight required to be used for a single bag of 8 feet capacity isnot less than 56 lbs. to 1 12 lbs. When two bags are used under pressurestart with 112 lbs., adding a 56 lb. and possibly a second 56 lb. towardsthe end. If a triple is in use it will require more weight than would asingle jet. The easiest form of weight for lifting and fixing steady on theboards are the square or oblong pattern, they can be bought at a price alittle above that of old iron.LIMESwhich appear insignificant in importance, practically, are a source oftrouble in consequence of the variations in quality, size, and boring.the quality to a great extent depends the light, and if the sizes areunequal when placed on the lime pin, the lime turner requires adjusting,and to replace and adjust a lime of this nature in the middle of anexhibition, when the jet is hot, is well nigh a feat of dexterity.The lime motion adjuster, mentioned on page 22 (figs. 15 and 16),overcomes this difficulty. The boring of a lime is not to be relied uponalways for its trueness, and is often too small, a watch-maker's broachpassed through the hole and worked round will soon enlarge it to theOn