CH. X] ERECT IMAGES IN DRAWINGS 369 



(B) If the mirror is very close to the objective (fig. 183) the 

 natural position for drawing is to sit facing the light. The object 

 then is put in position facing the objective as before, but upside 

 down. The image will appear erect on the drawing surface when 

 the observer faces the light. 



521. For a translucent, horizontal screen. In some of the 

 old forms of sketching apparatus the image was reflected upward 

 by a mirror or prism, and the artist drew on the upper surface. 



FIG. 209. DIAGRAM TO SHOW THAT THE SIZE OF THE IMAGE OF AN OBJECT 



DEPENDS UPON THE RELATIVE DISTANCE OF THE OBJECT AND IMAGE 



FROM THE CENTER OF THE PROJECTION LENS. 



(From. The Microscope}. 



In this figure the image is four times as far from the center of the lens (cl) 

 as the object, hence, from the law of similar triangles, the image must be four 

 times as long as the object. 



For such an arrangement, the object is put on the stage facing the 

 light, but right edge up. The image will appear erect on the 

 translucent screen when the observer faces the light and looks down 

 upon the screen. For this experiment the mirror or prism must be 

 on the lower side of the ocular (fig. 215). 



POSITION OF THE OBJECT FOR AN ERECT IMAGE WITH AN 

 OBJECTIVE AND AN OCULAR 



522. For an opaque vertical screen. The object should face 

 the light as with a lantern slide, but it must be right edge up. 

 With a microscopic specimen the cover-glass will be next the stage 

 as in 518. On the screen the image will appear erect (fig. 211). 

 The object on the stage will appear reversed like print seen in a 

 mirror (fig. 213). 



