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THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



shadowing effect shown clearly in the enlargement, but is not suitable for 

 determination of resolution or exhibition of plastic granularity on account 

 of the slightly imperfect focus, noticeable in the enlargement. Because the 

 replica was about 150 A thick, this granularity was scarcely evident even in 

 a perfectly focused micrograph, from which the resolution was estimated as 

 ranging upward from about 100 A. It should be observed that the direction 



Fig. 9— Aluminum replica (te = 180A, da = 30°) showing granularity due to recrystal- 

 lization. Local curling of replica has jesulted in "negative shadows" in upper left region 

 of stereogram. Resolution about lOOA. 



of maximum contrast in shading is as if a single source were toward the 

 lower right, about midway between the two actual sources whose azimuths 

 can be determined in the stereogram. 



The appearance of a micrograph of a replica which has undergone re- 

 crystallization on a scale comparable to h is shown in Fig. 9. The replica was 

 of aluminum; h was about 180 A, the lower limit of the optimum range; 

 da was 30°. The non-directional character of the granularity is evident. The 

 micrograph selected shows an area near a torn edge which has curled up- 



