388 HAYES— U. S. NAVY MV TYPE OF HYDROPHONE. 



This method of sounding, which is very simple in principle, is 

 not new. It differs from the first method described in that it depends 

 upon the accurate measurement of a tune interval (a difficult opera- 

 tion in practice), whereas the new method depends upon the meas- 

 urement of an angle (a comparatively easy operation). Moreover, 

 the error in soundings due to incorrect determination of the time 

 interval is as great for shallow as for deep water, whereas the error 

 due to incorrect determination of the sounding angle becomes very 

 small for shallow water. 



The velocity of sound in sea water at the ordinary temperatures 

 met in practice is roughly 4,4CX) feet per second. This velocity is so 

 great that stop-watch methods are not sufficiently accurate for meas- 

 uring the time intervals, since an error of one fifth second results in 

 a discrepancy of over 70 fathoms in the determining of depth. The 

 various laboratory methods of measuring time intervals with a high 

 degree of accuracy require a skilled operator and in general can not 

 be "employed on board ships. Several devices designed for marine 

 use in connection with this problem have been perfected but have all 

 proven to be too complicated to be successfully operated by a ship's 

 personnel. 



The writer is at present developing a new method which looks 

 very promising and by which the time interval between two signals 

 can be determined with a high degree of accuracy on shipboard. 

 The perfection of such a device will make possible the taking of 

 soundings with a fair degree of accuracy in water of any depth 

 while the vessel is steaming at full speed. 



Determination of the Range of a Sound-Source. 



If both a radio and an underwater sound signal are sent simul- 

 taneously from one point, the distance to the same can be determined 

 by measuring the time interval which elapses between reception of 

 the two signals at a distant point. In this way lightships or other 

 points provided with underwater navigation signals can be accurately 

 located. This procedure has been tried by stop-watch methods with 

 mediocre success, but it is believed that the device mentioned above 

 will make it possible to determine the range of a sound-source with 



