96 THE POPULAR SCIENCE MONTHLY. 



beam of sound projected through the funnel strikes the obstacle 

 and rebounds ; and as the echo is more or less perfect in propor- 

 tion as the obstacle is more or less parallel to the ship from 

 which the gun is fired, and as it is near or remote, the position 

 of the obstacle may thus be inferred. The board reported that 

 De la Torre's method was firing a blank cartridge from a rifle in 

 the presence of objects as small as a spar-buoy and as large as a 

 fort, and catching the return sound or echo. He claims that a 

 sharp sound projected at or nearly at an object, and only when 

 so directed, will in every case return some of the sound sent, so 

 that theoretically there will always be an echo, and the differ- 

 ence in the time between the sound sent and the echo will indi- 

 cate the remoteness of the object. The board found that a re- 

 turn-sound could be heard from the side of a fort a half-mile off, 

 from passing steamers a quarter-mile off if broadside-to, from 

 bluffs and sails of vessels about the same distance, and from 

 spar-buoys two hundred yards away. 



The board further states that the sound from the different 

 kinds of masses is different in most cases, and that the ear could 

 be educated to detect quite a range of different objects, as the 

 echo from a sail was different from the echo from a buoy or a 

 bluff. If two objects were near the line of projection at differ- 

 ent distances, an echo would be received from each. The hori- 

 zontal limit of the return of sound seemed to be about two 

 points on each side of the axis of projection. 



If Mr. De la Torre should see fit to construct his instrument 

 for hearing feeble echoes, the board indicated that it would rec- 

 ommend that it be fitted soon to some vessel of the North Atlan- 

 tic Station, and that further and, if possible, exhaustive experi- 

 ments ought to be made to practically determine the use of the 

 echo as a means to discover obstacles to navigation. It was also 

 stated that steam- whistles could be heard much farther than the 

 echo; but it was said that where the obstacle could not make 

 the sound, as in the case of an iceberg, the echo would be of the 

 greatest use, and experiments looking to its utilization are de- 

 manded by the conditions of navigation in time of fog. 



Steamers are constantly running among the islands on the 

 coast of Maine during the summer. This is the season of thick 

 and persistent fog. When pilots can hardly see the length of 

 their vessels, they keep up a constant noise with their fog-sig- 

 nals. The open sea gives back no sound. But the near or re- 

 mote vicinity of cliffs, bluffs, or even high shores, is indicated by 

 the strength of the echo received back from them. In fact, run- 

 ning by echo is recognized as one of the necessities of the navi- 

 gation of those waters. 



