VI P li F ACE. 



PREFACE TO SIXTH EDITION. 



MARCY'S SCIOPTICON is now no new thing. It has taken 

 its place as a standard projecting Lantern, and is accepted 

 as a great advance in this direction. As it becomes better 

 known, and less in need of explanations, the Sciopticon 

 Manual might be contracted rather than enlarged, only 

 that something more may be said to advantage of its new 

 attachments and new uses. It will ba seen that the Triple 

 Jet, the Gas Sciopticon, the Gas Microscope, etc., have been 

 improved since the illustrations prepared for the Fifth 

 Edition were drawn. 



The Automatic Cut-off is yet new to many, who will 

 stand in need of a fuller explanation in print. 



The description and illustrations of the Franklin Insti- 

 tute Gas Holders will interest Managers of Educational 

 Institutions. 



It is believed that all who are alive to the advantages of 

 photographic projections will find the Sciopticon Manual a 

 valuable Hand-book. 



