382 



SUMMARY OE CURRENT RESEARCHES RELATING TO 



its vertical axis. The mirror G should be turned about the axis of 

 the objective Q of 400 mm. focus. Fig. 107 represents this mode of pro- 

 jection, and shows the path of the rays. 



Fig. 108. 



5. Diascopic Projection (for horizontally-placed objects). — Apart from 

 its immediate purpose, that of projecting horizontal objects floating in 

 licmid, the arrangement has the advantage that lantern slides or sections 



