RESEARCHES IN SOUND. 465 



of powerful sound spread laterally, and even wlien projected from the 

 mouth of a trumpet, tend at a great distance to embrace the whole circle 

 of the horizon. 



Upon this and all the subsequent experiments, as it will appear, the 

 l^riuciple of reflection as a means of re-enforcing sound is but slightly n])- 

 plicable to fog-signals. It is evident however that the effect will be some- 

 what increased by augmenting the size of the reflector, and by more com- 

 pletely inclosing the source of sound in a conical or pyramidal reflector. 



Another series of experiments was made to ascertain whether the pen- 

 etration of the sound was greater in the direction of the axis of the bells, 

 or at right angles to the axis ; or, in other words, whether the sound was 

 louder in front of the mouth of a bell or of its rim. The result of this 

 experiment was considered of importance, since, in one of the light- 

 houses, a bell has been placed with the plane of its mouth at right angles 

 to the horizon, instead of being placed, as usual, parallel to the same. 

 The effect on the sound in these two positions was similar to that i)ro- 

 duced by the bell with a reflector, the noise being greater at a short 

 distance with the mouth toward the observer than when the rim was in 

 the plane of the ear. At a distance however, the difference between 

 the two sounds was imperceptible. In practice therefore it is of very 

 little importance whether the axis of the bell is perpendicular or liarallel 

 to the horizon. 



The flrst fog-signal examined in this series of experiments was a double 

 whistle, improperly called a steam-gong, designed i)rincii)ally for a fire- 

 alarm and for signals for the commencement of working-hours in large 

 manufacturing establishments. It consisted of two bells of the ordinary 

 steam-whistle on the same hollow axis, mouth to mouth, with a flat, hol- 

 low cylinder between them, through the upper and lower surface 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 

 circumstances more than twenty miles. It however reipiired a large 

 quantity of steam to give it its full effect, and the only means to obtain 

 an approximate idea as to this quantity was that afforded by observing 

 its action on a boiler of a woolen manufactory near Newport. It was 

 hei-e blown with a pressure of at least 75 pounds. From theoretical con- 

 siderations however, it might be inferred that its maximum penetrating 

 power would be not greater than that of a single whistle using the same 

 amount of steam, and this theoretical inference was borne out by the 

 subsequent experiments of General Duane. But from the strikingly 

 S. Mis. 59 — ^30 



