CH. VII] TROUBLES IN OPAQUE PROJECTION 195 



296. Troubles: 



i . The one great trouble will be a dim screen image. This can- 

 not be wholly avoided. It can be made tolerably good: 

 ( i ) by having the room very dark ; ( 2 ) by using a powerful 

 radiant; (3) by having a projection objective of large 

 aperture; (4) by magnifying the screen image very 

 moderately (5 to 10 diameters). 



FIG. no. MODEL 8 DELINEASCOPE FOR ALL KINDS OF PROJECTION. 

 (Cut loaned by the Spencer Lens Co.). 



In this instrument there is provision for lantern-slide projection with the 

 slides or other objeets in a vertical or in a horizontal position. 



It provides for opaque objects in a horizontal position and lighted directly 

 by the radiant (fig. in), and for objects in museum jars in a vertical or hori- 

 zontal position. 



Finally it provides for micro-projection with the objects in a vertical position 

 or in a horizontal position, and for the drawing of objects on a horizontal or on 

 a vertical surface. 



