1126 



EXPLORATION GEOPHYSICS 



by Batchellerf and by Stoddard* about 1900. A schematic arrangement of 

 the apparatus is illustrated in Figure 699. The pressure wave was created 

 by firing a pistol K, and the elapsed time between initiation n^ of this wave 

 and its reflection n^ was measured on a recording chronograph, actuated 



Fig. 699. — Early sound wave method of locating obstructions. (Batcheller, 

 U. S. Patent 602,422.) 



by a diaphragm H^. The trace M of a tuning fork of known frequency 

 was recorded on the record simultaneously to provide a means for measur- 

 ing time intervals accurately. 



A commercial incentive for this early work was furnished by the diffi- 

 culties encountered in operation of the underground pneumatic mail and 

 transport tubes in New York City, Philadelphia, Boston, etc. These tubes 

 were from six to eight inches in diameter and in some cases had lengths of 



t Birney C. Batcheller, "Apparatus for Locating Obstructions in Tubes," U. S. Patent 00S,422, 

 issued April 19, 1898. 



* Personal communication from Chas. F. Stoddard, formerly Chief Engineer, 

 American Pneumatic Service Company. 



