Introduction 



Although I do not propose to send out vibrations that 

 can be considered as sound from a musical standpoint, being 

 too low to appeal to the human ear, still, as these atmospheric 

 waves or vibrations only differ from audible sound vibrations 

 in their length, or, in other words, there are less of them 

 in a given time, and as they obey all the laws that govern 

 sound, I propose to treat them as sound and to designate 

 them as sound, although they are not audible to the human 

 ear. 



The siren furnished to Professor Tyndall by the United 

 States Government had a rotating disc 5 inches in diameter. 

 The trumpet was sixteen feet long, and the mouth measured 

 26 inches in diameter. It used steam at 70 Ibs. pressure to 

 the square inch, and gave off an audible note. The prob- 

 abilities are that when the steam valve was wide open the 

 power represented would not be more than 50 h.p. 



On our large steamships, we very often have a boiler 

 pressure of 280 Ibs. to the square inch. Suppose, now, that 

 we use a rotating disc 10 inches in diameter and a trumpet 

 correspondingly large, we can convert 500 h.p. into sound, 

 sending out vibrations of enormous energy and amplitude, 

 which ought to travel over a distance very much greater than 

 would be possible with any of the instruments employed by 

 Professor Tyndall. As the steam valve of a siren is only 

 open for about a second at a time, it is very evident that the 

 total amount of steam consumed would not be very great, 

 although -the energy when it was actually escaping might be 

 500 h.p. 



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