SEISMIC METHODS 



827 



Fig. 510. — Sonograph records showing 2 five-track films and 3 

 ten-track films, a, typical correlations made by comparing light 

 bands; b, shot-breaks. (Courtesy of Rieber Laboratories.) 



noise as well as against signals arriving from any but the selected direction. 

 A series of time-delays associated with another direction of wave arrival 

 is then introduced and the composite wave for this direction studied. f 

 The time delays are introduced by mechanically adjusting the relative 

 positions of the detecting slots along the time axis of the density-modulated 



t Another system for determining ^T values utilizes magnetic recording and play-back. See 

 J. D. Eisler and J. A. Sharpe, "Recording System in Seismic Prospecting," U. S. Patent 2,394,990, 

 Feb. 19, 1946. 



F. Rieber, "Apparatus and Method for Making and Analyzing Geophysical Records" (Mag- 

 netic Recording), U. S. Patent 2,427,421, Sept. 16, 1947. 



