July, 1913. 



KNOWLEDGE. 



271 



Figure 272. 



A Liliput arc- 

 lamp placed in 

 position for use 

 with the con- 

 denser. 



Figure 273. 

 Central stop. 



Figure 275. 



An objective with 

 the nickel-plated 

 part unscrewed. 



Figure 276. 

 1'he intersecting pencils of light within fluorescent uranium glass 



Figure 274. 



Two of the loose 

 discs. 



Figure 278. 



Snapshot taken 

 upon an ortho- 

 chromatic plate 

 with the aid of a 

 screen. Repro- 

 duced from a 



platinum print. 



(See page 274.) 



Figure 277. 



Diagram of the condenser and 



an immersion objective. The 



dotted lines indicate the pencils 



of light. 



