90 THE POPULAR SCIENCE MONTHLY. 



can "be arranged by which the aberration in the audition of the 

 mariner may be so corrected that he can locate the source of 

 the sound which is made to assure his safety, but which, mis- 

 heard, may, as in the case of the Edam and Lepanto, insure 

 his destruction. 



It seems evident from President Morton's statements that if 

 the fog-signals of the maritime world, or even of one country, 

 or even those located in the approaches to one of our great har- 

 bors, were tuned to one note, and if the ships frequenting those 

 waters were fitted with topophones, or some similar instrument, 

 arranged so as to be in unison with the fog-signals, that aberra- 

 tions in audition, at least as to direction, might be corrected, so 

 as to determine the location of sound to within at least one com- 

 pass-point. 



Since the development of the topophone a number of other 

 instruments have been invented for determining for the mariner 

 the direction of sound made to warn him from danger. For 

 some time some of our best ocean-steamers have been supplied 

 with an instrument giving sounds of wonderful pitch and in- 

 tensity, called the siren. It was adapted from the instrument 

 invented by Cagniard de la Tour, by A. and F. Brown, of the 

 New York City Progress Works, under the guidance of Prof. 

 Henry, at the instance and for the use of the United States 

 Lighthouse Establishment, which also adopted it for use as a 

 fog-signal. The siren of the first class consists of a huge trum- 

 pet, somewhat of the size and shape used by Daboll, with a wide 

 mouth and a narrow throat, and is sounded by driving com- 

 pressed air or steam through a disk placed in its throat. In this 

 disk are twelve radial slits ; back of the fixed disk is a revolving 

 plate containing as many similar openings. The plate is rotated 

 2,400 times each minute, and each revolution causes the escape 

 and interruption of twelve jets of air or steam through the open- 

 ings in the disk and rotating plate. In this way 28,800 vibra- 

 tions are given during each minute that the machine is oper- 

 ated ; and, as the vibrations are taken up by the trumpet, an in- 

 tense beam of sound is projected from it. The siren is operated 

 under a pressure of seventy-two pounds of steam, and can be 

 heard, under favorable circumstances, from twenty to thirty 

 miles. "Its density, quality, pitch, and penetration render it 

 dominant over such other noises after all other signal-sounds 

 have succumbed." It is made of various sizes or classes, the 

 number of slits in its throat-disk diminishing with its size. This 

 instrument is now used as a fog -signal by most maritime 

 nations, they having frankly copied from, and, in some in- 

 stances, obtained it through the United States Lighthouse Es- 

 tablishment; and it has been recently adapted to the use of 



