RESEARCHES IN SOUND. 467 



the bealtb of the crew is an objection to the iutroductiou of this modi- 

 fication of tlie apparatns into light-ships. 



The other instruments which were subjected to trial were an ordinary 

 steam-whistle and a Daboll trumpet. The bell of the whistle was 

 inches in diameter, 9 inches in height, and received the sheet of steam 

 through an opening of one-thirtieth of an inch in width ; was worked 

 by a pressure of condensed air of from 20 to 35 pounds per square inch, 

 and blown once in a minute for about five seconds. The air was con- 

 densed by a Koper engine of one-horse power. The penetrating power 

 of the sound was increased by an increase in the pressure of the air, 

 and also the pitch. The tone however of the instrument was lowered 

 by increasing the distance between the orifice through which the circular 

 sheet of air issued at the lower rim of the bell or resounding' cavity. 

 To prove conclusively that the bell performs the part of a mere resound- 

 ing cavity, a wooden one, on a subsequent occasion, was substituted for 

 that of metal without a change in the loudness or the pitch of the sound. 



The penetrating power of the whistle was compared with a Daboll 

 trumpet, actuated by an Ericsson engine of about the same power ; the 

 reservoir for the condensed air of each machine was furnished with (i 

 pressure-gauge, and by knowing the capacity of the condensing i)umps 

 and the number of strokes required to produce the pressure, the relative 

 amount of power was determined. The result was that the i^enetrating 

 power of the trumpet was nearly double that of the whistle, and that an 

 equal effect was produced at the same distance by al)out one-fourth of 

 the power expended in the case of the latter. It must be recollected 

 however, that the whistle sends sonorous waves of equal intensity in 

 every direction, while the greatest power of the trumpet is in the direc- 

 tion of its axis. This ditference however is lessened on account of the 

 spreading of the sound to which we have before alluded.* The whistle 

 was blown, as we have said, with a pressure of from 20 to 35 pounds, 

 while the trumpet was sounded with a pressure of from 12 to 15 jiounds. 

 In the case of the whistle, the pressure in the reservoir may be indefi- 

 nitely increased with an increase in the penetrating i)ower of the sound 

 produced, while in the case of the trumpet a pressure greater than a 

 given amount entirelj^ stops the blast by preventing the recoil of the 

 vibrating tongne ; this being made of steel, in the larger instruments 

 2^ inches wide and 8 inches long, would receive a j^ressure of steam, at 

 only 10 pounds to the square inch, of 200 pounds, tending to press it 

 into the opening and to prevent its recoil, this circumstance limits, as it 

 were, the power of a trumpet of given dimensions. It is however well 

 fitted to operate with a hot-air engine, and is the least expensive in fuel 

 of any of the instruments now employed. The whistle is the simpler 

 and easier of management, although they both require arrangement of 

 machinery in order that they may be operated automatically. 



* It is worthy of uote however that in the case of a sound having primarily an axial 

 direction, the subsequent lateral ditl'usion must result in enfeebling the whole sphere 

 of expanding sound-waves in a more rapid ratio tliau the square of the distance. 



