100 THE ART OF PROJECTING. 



ment (Fig. 27). When water is poured in to fill it, 

 the light will be refracted and an object may be pro- 

 jected with it as with any other lens. 



Fig. 76. 



The formation of images by lenses is well shown by 

 holding a lighted candle or lamp in front of the screen 

 at any distance in a darkened room, and bringing the 

 lens close to the light, then moving it towards the 

 screen until the inverted image appears. Try this 

 with double convex and with plano-convex lenses of 

 different focal lengths, also with a meniscus and with 

 a concave lens. 



THE SOLAR MICROSCOPE. 



This has been described on a former page, and may 

 be turned to ; but, as nearly all of the art of projection 

 depends upon the use of lenses, it will be well, in 

 giving instruction to dwell upon the conditions for 

 forming images with single and with compound lenses, 

 with parallel converging and diverging beams. The 

 porte lumiere, the magic lantern, the solar microscope, 

 the telescope, may be illustrated by methods that have 

 been already explained. 



THE RAINBOW. 



This phenomenon in nature is due to refraction and 

 reflection in drops of water. It is hardly practicable 



