. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. rocking mirror, capable of giving amotion to the spotof light at rightangles to that givenby the this rockingmotion should begiven, backwards andforwards, so that the motion synchronises with the pulse-motion ; when the breakin the curve will be seen very fairly represented on the screen. It is true that this break can only be followed for onepulse at a time, and not for many beats together as in atracing. But there is a general remark to be made here re-specting the true p
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. rocking mirror, capable of giving amotion to the spotof light at rightangles to that givenby the this rockingmotion should begiven, backwards andforwards, so that the motion synchronises with the pulse-motion ; when the breakin the curve will be seen very fairly represented on the screen. It is true that this break can only be followed for onepulse at a time, and not for many beats together as in atracing. But there is a general remark to be made here re-specting the true place and value in demonstration of directprojections. Exhibited thus, however roughly, they give asense of vivid objective reality which can be imparted to aclass in no other way, to tracings prepared by any of thewell-known methods, and which should immediately after-wards be projected upon the screen, using the tracings asordinary scientific diagrams. To obtain such slides, eitherthe revolving blackened cylinder so usual in tracing apparatusmust be displaced for tracing on the flat, which is most. FiCr. 120.—r-ulse Mirror 234 OPTICAL PROJECTION easily and simply done in ways too obvious to need descrip-tion ; or films of smoked mica can be bent round the cylinders,and afterwards unrolled and mounted between glass take the case before us : when the break in the curve hasonce been shown in actual motion on the screen by the pulse-mirror, and its method of production explained, it will befound that the meaning of the curve in any tracings subse-quently projected will be instantly realised in a degree verydesirable. This will be still more the case if the process of tracingbe itself projected, which can generally be done, by the ap-
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
