CH. X] ERECT IMAGES IN DRAWINGS 367 



It is a good plan to have a specially prepared microscopic slide or 

 a lantern slide with print at hand whenever one is going to draw, 

 then one can determine quickly and exactly how the specimen 

 should be placed to give an erect image. A simpler method still 

 is to write the letters, a, k, on the cover of the specimen to be 

 drawn (512, fig. 220). 



POSITION OF THE OBJECT FOR ERECT IMAGES WITH THE PROJECTION 



MICROSCOPE AND AN OBJECTIVE ONLY, OR WITH AN OBJECTIVE 



AND AN AMPLIFIER 



518. For an opaque vertical screen. Place the object on the 

 stage as a lantern slide is placed in its carrier (35), that is, with the 

 specimen facing the light and the lower edge up. With a micro- 

 scopic specimen this would bring the cover-glass next the stage and 

 facing away from the objective instead of toward it, as in ordinary 

 microscopic observation. In this case one must focus through the 

 slide instead of through the cover-glass. This can, of course, be 

 done with low, but not with high powers. (See drawing on a hori- 

 zontal surface 524). 



With the specimen placed as directed, the image on the vertical 

 opaque screen will appear erect in every way (fig. 211). 



If one faces the light and looks at the specimen on the stage it will 

 look like fig. 214 that is, like print seen through a sheet of paper 

 wrong side up. 



519. For a translucent vertical screen. If the screen is of 

 ground-glass like that of a photographic camera, or if it is of tracing 

 paper or other translucent substance supported by clear glass, the 

 object should be placed on the stage so that it faces the objective, 

 and is lower edge up. 



When the observer looks at the image on the translucent screen, 

 i. e., facing the light, the image will be erect like fig. 211. 



When he faces the light and looks at the object on the stage it will 

 appear like fig. 212, i. e., it is simply upside down. 



