. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. for each, a drop of fluid is intro-duced by the point of the brushinto each separate mesh. Thisis easily done so as to exhibit ageometrical pattern, which whenmagnified has a wonderfully fineeffect upon the screen. By drawing the brush over themeshes the effect is different,and will resemble that of Berlin-wool-work upon a large scale,the colour always running out tothe edges of exact squares. Experiments with fluids intubes project better if the tubescan be somewhat flattened whilstred-hot.
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. for each, a drop of fluid is intro-duced by the point of the brushinto each separate mesh. Thisis easily done so as to exhibit ageometrical pattern, which whenmagnified has a wonderfully fineeffect upon the screen. By drawing the brush over themeshes the effect is different,and will resemble that of Berlin-wool-work upon a large scale,the colour always running out tothe edges of exact squares. Experiments with fluids intubes project better if the tubescan be somewhat flattened whilstred-hot. The flat sides are ofcourse turned towards condenserand screen, the object being toget more surface and a nearerapproach to one focal is readily projected from the usual apparatusshown in fig. 113, using a nearly capillary tube, which is pro-jected, and rather large membranous bag, and staining theinternal fluid. If the tube is sufficiently small in propor-tion, the rise of the fluid in it will readily be seen in pro-gress. 118. Surface Tension.—The tension of liquid surfaces is. Fig. 113 DEMONSTRATIONS IN PHYSICS 225 best shown by projecting flat soap-films in circular rings,1 thearrangement of the apparatus being shown in detail at p. 327,where the bands of colour are being projected. At present,however, we are not dealing with colour, but simply with thecontractile power of the film. Having lifted a film from thesaucer, lay across it a loose thread of fine sewing-silk dippedin the solution ; this thread will also be projected, and it willbe seen that it may be moved about freely. Prick on eitherside of the thread with the end of a small screw of blotting-paper, and the tensile force on the other side at once drawsthe thread into a curve as fig. 114. In the same way a looseclosed loop, pricked in the centre, is at once drawn out into
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
