120 



MAGIC LANTERN WITH OIL AND GAS LAMPS [Cn. V 



which showed general form and details with anything like satisfac- 

 tion to large audiences. But screens as large as four meters square 

 (12 ft. sq.) were used with the petroleum light. 



When the feeble lights discussed in this chapter are compared 

 with the powerful electric arc light giving from 1,000 to 5,000 candle- 

 power it would seem that the results of earlier times must have been 

 very unsatisfactory. 



But the older lanternists gave very successful exhibitions. They 

 did this by observing with scrupulous care the requirements for 

 projection with their appliances. 



Condenser 



FIG. 64. MAGIC LANTERN WITH LARGE LIGHT SOURCE. 



Lamp Illuminating gas lamp with Welsbach mantle. 

 Condenser Triple-lens condenser without water-cell. 

 S Lantern slide. 



Objective Projection objective with inverted image of the luminous mantle 

 between the lenses. 



Screen Image The image of the lantern slide on the white screen. 



193. Requirements for projection with a feeble light: 



(A) The lantern slides must be very transparent ; and the old, 

 hand-painted slides were very transparent. 



(B) The room must be very dark. There must be no stray 

 light from the windows or from the apparatus ; the only light must 

 be that issuing from the lantern objective and reflected from the 

 screen . 



(C) The management of the lantern must be the best possible, 

 so that all the available light may be utilized for producing the 

 screen image. 



(D) The projection objective must be of large aperture so that 

 as much as possible of the light issuing from the large source (lamp 



