CH. I] DO AND DO NOT WITH THE MAGIC LANTERN 



67 



20. Study the "Troubles," 

 their causes and remedies (62- 

 98). 



21. Focus the screen image 

 sharply, using opera-glasses, if 

 necessary (38). 



20. Do not fail to study the 

 "Troubles" and their remedies. 



21. Do not let the screen 

 image appear vague and out of 

 focus. Do not forget the aid 

 opera-glasses will give, if the 

 screen distance is great. 



