CH. IX] 



TROUBLES WITH'MICRO-PROJECTION 



309 



439. Dark spots on the screen. 



i. They may be caused by air bubbles in the water-cell or in 

 the stage cooler. 



FIG. 174. SIMPLE ADDITION TO THE MAGIC LANTERN FOR 

 MICRO-PROJECTION. 



(Cut loaned by the Spencer Lens Co.). 



This consists of a jointed frame by which the objective holder and focusing 

 device can be brought down in position when the lantern-slide objective is 

 turned aside. No microscope tube is used. This makes a very efficient and 

 convenient addition to a magic lantern at moderate cost, and with it a great 

 deal of projection can be successfully accomplished. 



For lantern-slide projection the microscope is turned to the top of the lamp 

 enclosure and the lantern-slide objective is turned on its hinge back into posi- 

 tion in the optic axis. 



2 . They may be caused by dark spots or bubbles in the slide or 



specimen. 



3 . Dark spots on the condenser, amplifier or ocular may cause 



them. 



440. General conditions for good micro-projection. With 

 good specimens, clean glass surfaces, and all the elements on one 

 axis, there should be no trouble in getting a good screen image on a 

 suitable screen and in a well darkened room. 



It would be of very great advantage for any man who aspires to 

 use the projection microscope effectively, if he could see the room, 

 apparatus, and exact method of work of some one who had mas- 

 tered the art. Good projection will not do itself. 



