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periments and some mathematics, Dr. Penney learned 

 how to translate bends into pressure values.* 



Dr. Penney 's group was not the only one striving 

 to extract knowledge from the pressure wave. The 

 problem was attacked on a very broad front by the 

 powerful Bureau of Ordnance Instrumentation Group. 

 This Group, led by Captain A. E. Uehlinger (Navy) 

 and under the technical direction of Dr. G. K. Hart- 

 mann, surveyed all known types of pressure gages. 



But finding suitable gages was difficult ; there were 

 many hard-to-meet requirements. Some of these re- 

 quirements pervaded the other scientific fields, and 

 were thus of especial importance. 



Most important was the requirement that the gages 

 leave permanent records of their response; there 

 would be no one on hand to watch them. Among the 

 various automatic recording schemes available were: 

 (1) ink-recorders, in which a small fountain pen writes 

 its crude but significant message automatically on a 

 sheet of paper mounted on a slowly-rotating disk or 

 drum; (2) scratch-recorders, in which a needle 

 scratches its message on a wax-coated disk or drum; 

 (3) magnetic recorders, in which variations in pressure 

 are converted into variations in degrees of magnet- 

 ization of a short segment of a slowly-moving steel 

 wire or tape; (4) optical recorders, in which pressure 



* /?i his official tour of inspection of Hiroshima and Nagasaki, 

 Dr. Penney had found that the pressure waves there had left read- 

 able records in the form of bent fence posts, sign posts, etc. 



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