Fig. 4. 



THE CAMERA OBSCURA/ 



1. Principle of the instrument. 2. Its inventor. 3. Method of mount- 

 ing it. 4. Application of the prism to it. 5. Mounting a camera 

 with prism. 6. Portable camera. 7. Form of camera adapted to- 

 photography. 



1. THIS is an instrument of extensive utility in the arts of 

 design; by it the process of drawing is reduced to that of mere 

 tracing, and its use has of late been greatly extended by its appli- 

 cation in the art of photography. 



"We have already explained, in our Tract upon "Optical 

 Images," that if a convex lens, or any equivalent optical combina- 

 tion, be presented to a distant object, such as a landscape, an 

 inverted image of that object, with its proper outline and colours, 

 will be produced at the principal focus of the lens. Let us sup- 

 pose, for example, that the window-shutters of a chamber being 

 closed, so as to exclude the light, a hole be made in them, in 

 which a convex lens is inserted : let a screen made of white paper 

 be then placed at a distance from the lens, equal to its focal 



Two Latin words, ^signifying "a dark chamber." 



203 



