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THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



optimum. Crystallite size is probably less than 50 A. As in Fig. 10, the granu- 

 larity is probably due to plastic. A thin, torn film appears in the shadow. 

 From the extreme sharpness of a portion of one edge of the shadow, al- 

 though slightly complicated by granularity, one concludes that instrumental 

 resolution is better than 50 A. Replica resolution is about 100 A. Despite 

 the smaller value of da, the thick replica provides a greater range of tone 



Fig. 11 — Composite replica of Al, 

 Mg/cm^. Resolution about lOOA. 



Pt, Cr.^a = 30°. Mass thickness probably 10-12 



values, as compared with Fig. 7, although this may not be evident in the 

 reproductions. 



Figure 11 shows a micrograph from a composite replica of aluminum, 

 platinum, and chromium. Aluminum and platinum were simultaneously 

 evaporated from a tungsten wire which burned out before the evaporation 

 was complete. If all the aluminum evaporated before the platinum, its 

 thickness was about 50 A. The amount of Pt is problematical, but the 

 chromium, evaporated after the tungsten wire was replaced, had a thickness 

 of about 100 A. The same angle, Ba — 30°, was used in the two evaporations. 



