TAKING PICTURES 



127 



wet while it was being exposed in the camera. About 1850 

 the dry plate was invented, and this marked a great advance 

 in photography. The next great improvement was the use 

 of films in place of glass for the negatives. Meanwhile great 

 improvements were made 

 also in the construction 

 of the camera. 



The camera. An ordi- 

 nary focusing kodak (see 

 figures 40 and 41) consists 

 of the following parts: a 

 light-proof box, which may 

 be drawn out in the form 

 of a bellows, a lens in the 

 front end of this, which 

 focuses an image on a film 

 or plate placed at the back 

 of the box. In front of 



FIG. 40. Folding camera. 



the lens is the diaphragm 

 with an adjustable open- 

 ing in the center through which the light passes, and the 

 shutter by means of which the exposure is made. On the 

 front is a finder by means of which those objects that will 

 appear in the picture may be seen. 



DEMONSTRATION 15 



Purpose. To show how a camera forms images. 



Apparatus. Convex lens, cardboard, camera. 



Directions, i. Hold a piece of cardboard on the side of a 

 convex lens away from a window. Move the cardboard back 

 and forth until a distinct image of the window is formed on it. 

 How does the image differ from the object? 



2. Take a camera apart and notice the use of each part in 

 taking a picture. 



