182 BELL SYSTEM TECHNICAL JOURNAL 



for encouragement of scientific research to increase metal recovery. 

 The United States is favored above most nations in being largely self- 

 contained with respect to original sources of economic metals, yet it 

 has no source for tin and platinum and inadequate sources for man- 

 ganese, chromium and other less common metals essential to present- 

 day steels. 



The work of a joint commission of the American Institute of Mining 

 and Metallurgical Engineers and the Mining and Metallurgical Society 

 of America is outlined, giving briefly their recommendations for inter- 

 national control of minerals. 



The paper is concluded by emphasis of the importance of secondary 

 metal recovery to national existence in times of stress when the nation 

 may be thrown entirely upon its own resources. The conclusion also 

 makes an appeal for the consideration of international conventions on 

 economic metal exchanges and suggests that competent technical men 

 be taken more into political councils in the treatment of a problem of 

 this kind. 



Tone Reproduction in the ^^ Halftone'' Photo-Engraving Process.'^ 

 Herbert E. Ives. The "halftone" photo-engraving process was 

 invented, and its technique developed, prior to the days of what is 

 commonly called "photographic sensitometry." The necessary con- 

 ditions and the appropriate operations for securing "highlight" and 

 "shadow detail " were found by empirical studies guided by the 

 appearance of the result, as appraised by the unaided eye. No 

 comprehensive sensitometric study of the halftone reproduction process 

 appears to have been made, at any rate none have been published. 

 The work described is a rough survey of the problem, but, due largely 

 to the use of accurate photometric measurements, and the correlation 

 of these measurements with other sensitometric data, rather decisive 

 conclusions have been possible as to the essential characteristics of the 

 process in question, and on the procedures necessary for its complete 

 success. 



Frequency Measurements with the Cathode Ray Oscillographs 

 Frederick J. Rasmussen. The cathode ray oscillograph frequency 

 measurement circuit described, differs from previous circuits in the use 

 of by-pass condensers and plate leaks which permit the connection of 

 the oscillograph to a.-c. circuits having large d.-c. components and 

 which permit the use of biasing controls for shifting the position of 

 patterns on the screen. 



^ J.O. S. A. and R. S. I., March, 1926, p. 537. 



5 Presented before the A. L E. E., New York, N. Y., Nov. 1926. 



