THE STROBOSCOPIC EFFFCT 



2i»:', 



was one of the preliminary experiments to find a method to 

 replace that of the manometric flame, for the purpose of stro- 

 boscopy. A reflected beam falling on a rotating mirror gave 



Fig. 21. 



clearly defined sine waves of large amplitude. A simple step 

 from this arrangement was to attach the small mirror directly 

 to the membrane, and then to use a mica membrane that could 

 be entirely silvered. 



B of figure 21 shows, above, a reflecting membrane made by 

 stretching paper over the large end of a telephone receiver shell 

 with the cap off, and to the paper attaching as already indi- 

 cated a mica mirror. Below is shown a glass tube arrangement 



