212 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1915. 



heard. Since sound travels in water at a velocity of approximately 

 4,400 feet per second, if the distance be 100 feet, the time taken by 

 the sound in traveling from ship to bottom and from bottom to ship 

 will be approximately one-twentieth of a second. 



In April, 1914, some tests were made on the U. S. revenue cutter 

 Miami to see whether soundings could be taken in the manner above 

 indicated. As the commutator had not been completed, a temporary 

 apparatus with a stop watch was used. The echo from the bottom was 

 plainly heard not only on the oscillator but in the wardroom and in 

 the hold of the ship without any instruments whatever. The elapsed 

 time corresponded to the depth shown on the chart, and the proposed 

 method Avas proved to be feasible. 



The chief object of the tests on the Bliwmi was, however, to deter- 

 mine whether a reflection from icebergs could be obtained, and this 

 was proved beyond question. The apparatus used was the same as 

 for taking soundings. 



A signal was sent on the oscillator, the echo from the bottom heard, 

 and then the echo from thfe iceberg came in. To make sure that the 

 second echo was not also from the bottom, the distance from the 

 Miami to the iceberg Was varied from about 100 yards to 2J- miles. 

 The elapsed time between the signal and the echo from bottom re- 

 mained the same, but the elapsed time of echo from the icelierg varied 

 with the distance and corresponded very closely to the position of the 

 iceberg determined by the range finder. Moreover, it was found that 

 it made no difference whether the face of the iceberg was normal to 

 the path of the sound or not, thus showing that the echo was due not 

 to specular reflection but to diffraction fringes. 



When the Miami had gone 2| miles from the iceberg a heavy storm 

 made it necessary to postpone further tests, and continued rough 

 weather made further tests impossible, as the oscillator Avas not per- 

 manently installed but had -to be lowered overboard. The echoes at 

 2^ miles were, however, loud, and there can be no doubt that they 

 would have been heard at greater distances. (See appended report 

 of Capt. Quinan.) 



To sum up: The oscillator represents an important step forward 

 in the science of navigation. It makes it possible to surround the 

 coasts with a wall of sound so that no ship can get into dangerous 

 waters without warning, to make collisions between ships possible 

 only through negligence. Although no sufficient tests have been made 

 to warrant the statement that icebergs can be detected under all 

 circumstances or that soundings can be taken at full speed, what 

 evidence there is points that way. For naval purposes it provides 

 an auxiliary means of short-distance signaling that is available at 

 all times and that can not be shot away, and it widens the possibili- 

 ties of submarine boats to an extent we can not yet fully grasp. 



