246 



KNOWLEDGE. 



July, 1913. 



Figure 250. 

 Rough castings as received at the works. 



Figure 252. 

 Optical glass as imported. 



Figure 251. 

 Planing the surface of a fine adjustment by hand. 



Figure 253. 

 Machine for slitting the glass. 



Figure 254. 

 Roughing or getting the lenses into shape for polishing. 



Figure 255. 

 Lens polishing machine with blocks of lenses. 



