382 WRITINGS OF JOSEPH HENRY. [1874 



with a flat, hollow cylinder between them, through the upper 

 and lower surfaces of which the circular sheets of steam issue, 

 the vibration of which produces the sound. In the instrument 

 under examination, the upper bell was 20 inches in length 

 of axis, and 12 inches in diameter, and the lower whistle 

 was of the same diameter, with a length of axis of 14 inches. 

 The note of the shorter bell was a fifth above that of the 

 longer. This arrangement gave a melodious sound, unlike 

 that of the ordinary locomotive-whistle, and on that account 

 had a peculiar merit. The sound was also very loud, and 

 according to testimony — had been heard under favorable cir- 

 cumstances more than twenty miles. It required a large 

 quantity of steam however, to give it its full effect, and the 

 only means to obtain an approximate idea as to this quan- 

 tity was that afforded by observing its action on a boiler of 

 a woolen manufactory near Newport. It was here blown 

 with a pressure of at least 75 pounds. From theoretical 

 considerations however, it might be inferred that its maxi- 

 mum penetrating power would not be greater than that of 

 a single whistle using the same amount of steam, and this 

 theoretical inference was borne out by the subsequent experi- 

 ments of General James C. Duane. But from the strikingly 

 distinctive character of its tone it has in our opinion an 

 advantage over a single whistle expending an equal quantity 

 of steam. 



The fact that the vibration of the metal of the bell had 

 no practical effect on the penetrating power of the sound 

 was proved quite conclusively by winding tightly around 

 each bell, over its whole length, a thick cord, which would 

 effectually stop all vibration. The penetration of the sound 

 produced under this condition was the same as that with 

 the bells free. It is true, the latter produces a difference in 

 the quality of the tone, such as that which is observed in a 

 brass instrument and that of one of wood or ivory. The 

 inventor was not aware that the sound produced was from 

 the resonance of the air within the bell, and not from the 

 metal of the bell itself, and had obtained a patent, not only 

 for the invention of the double whistle, but also for the 

 special compound of metal of which it was composed. 



