. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. ece CD (fig. 99)being brought to that spot, the lens F will stand on that at the requireddistance. This general arrangement governs all experiments where focussinghas to be done after the deflection of the rays, by reflection or otherwise, hagbeen effected. 328 OPTICAL PROJECTION Sometimes the heat of the lantern will destroy the filmtoo rapidly. In that case an alum cell in the slide-stage willremove the difficulty. Horizontal bands being caused by the action of gravitationon the film, if w
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. ece CD (fig. 99)being brought to that spot, the lens F will stand on that at the requireddistance. This general arrangement governs all experiments where focussinghas to be done after the deflection of the rays, by reflection or otherwise, hagbeen effected. 328 OPTICAL PROJECTION Sometimes the heat of the lantern will destroy the filmtoo rapidly. In that case an alum cell in the slide-stage willremove the difficulty. Horizontal bands being caused by the action of gravitationon the film, if we can make the gradual thinning take acircular form, the bands will become annular. This iseffected by a beautiful modification of the experiment oftenemployed by Lord Eayleigh, and which is very easy if anysort of bellows, or weighted bag filled with air, be at hand,to furnish a slight blast. Even the breath will answer, butneeds some practice and a thin rubber balloon to steady thepressure. Connected with the air-blast (a gentle one) byrubber tubing is a piece of glass tube drawn into a small but. Fig. 180.—Eotating Films not capillary orifice: one of the fillers sold for use withfountain pens answers excellently. This is fixed in anothersmall Bunsen holder, and adjusted so as to direct a blast at asmall angle with the surface of the film. Adjusted near theedge as at a (fig. 180) the above is converted into a singlewhirling vortex, which shows rapid and magnificent gradationof colour: adjusted as at b, a little to one side of the centre,the stream divides into two vortices, in which the play ofcolour is still more rapid. This experiment never fails tobring down the house. 187. Films of air—Newtons Kings.—Two squares of plateglass, with rounded edges, cleaned and polished, are readily INTERFERENCE OF LIGHT 329 worked together till they show beautiful air-films. It is wellthen to keep them together with spring wooden clips, one ateach corner, pinching one corner in the Bu
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
