CHAPTER XV 



SOME USES OF PROJECTION IN PHYSICS ; EXPERIMENTS 



ILLUSTRATING NORMAL VISION AND SIMPLE, 



REFRACTIVE EYE DEFECTS. 



875. Apparatus and Material for Chapter XV: 



For polarized light, see 879; For projection of spectra, see 

 885; For photography, see 908; For Abbe Diffraction Theory, 

 see 909; For eye defects, see 916. 



876. Historical development of experimental projection. 



Works of reference giving methods of projecting experiments. 



In every book, and in every article on projection, directions and 

 hints are given. The following are especially full in directions, and 

 rich in suggestions : Dolbear. The Art of Projecting; Fourtier et 

 Moltini . Les Projections Scientifiques ; Hassack und Rosenberg. 

 Projektions-apparate ; Lehmann. Flussigekrystalle ; Trutat. - 

 Traite des Projections ; Tyndall. Six lectures on light ; Wright. 

 Light, a course of experimental optics chiefly with the lantern; 

 Wright. Optical Projection. 



INTRODUCTION 



877. Many physical and chemical experiments can be 

 exhibited to an entire class in a striking manner by the aid of 

 projection apparatus. Sometimes transparent objects are used, 

 and then again, as suggested by Dolbear, many experiments with 

 opaque objects show very clearly as shadows on the screen if they 

 are performed in the beam of the magic lantern. 



Indeed, for exhibiting to a class or any large audience the varied 

 experiments necessary in physical and chemical work, all the pro- 

 jection apparatus described in this book and combinations of them 

 may be needed. By thoroughly mastering the principles of projec- 

 tion one can so adjust and combine the different pieces of appara- 

 tus that almost any phenomenon can be shown on the screen. 



One can find many suggestions, and often detailed directions for 

 showing various experiments in the works referred to at the begin- 

 ning of this chapter. 



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