CH. I] 



vSOME AMERICAN MAGIC LANTERNS 



61 



PIG. 35. SECTIONAL VIEW OF AN ARC LAMP AND A TRIPLE-LENS 

 CONDENSER WITH WATER-CELL. 



+ W Wire going to the positive carbon. 

 W Wire from the negative carbon. 



He Horizontal or upper carbon ; it is positive. 



Vc Vertical or lower carbon ; it is negative. 



L The crater of the positive carbon ; it is the source of light. 



Cond I The first element of the triple-lens condenser. The meniscus is 

 always placed with the concavity next the source of light. 



Cond 2 The second element of the triple-lens condenser. It is a plano- 

 convex lens and should be of the same focus as the projection objective. The 

 different lenses should be in the position shown in this diagram. Between the 

 two convex lenses in the parallel beam of light is placed the water-cell. 



B I B 3 Blocks supporting the arc lamp and the condenser. 



Base The base-board with the track along which the different parts move 

 (see fig. 40). 



Axis The principal optic axis of the condenser and continuous with that 

 of the projection objective. 



FIG. 36 A. MAGIC LANTERN WITH AN AUTOMATIC LAMP AND INCLINED 



CARBONS. 

 (Cut loaned by P. Keller & Co., successors to the J. B. Coll Co.). 



This lantern is very widely used. It has a two-lens condenser (see fig. i). 

 Its main defect is that every part, lamp, condenser lantern-slide holder and 

 objective can be separately raised or lowered. 



