474 RESEARCHES IN SOUND. 



succession, thus producing a rapid series of impulses of steam against the 

 air into the smaller orifice of the trumpet placed immediately in front of 

 the revolving disk. These impulses are of such intensity and rapidity 

 as to produce a sound unrivalled in magnitude and penetrating power 

 by that of any other instrument yet devised. 



The siren was operated by an upright cylindrical tubular boiler, with 

 a pressure of from 50 to 100 pounds on the square inch. For this form 

 of boiler has been subsequently substituted an ordinary horizontal 

 locomotive-boiler with a small engine attached for feeding it and for 

 rotating the disk, the latter being effected by means of a band passing 

 over pulleys of suitable relative dimensions. 



3d. A steam-whistle 8 inches in diameter. Through some misunder- 

 standing a series of whistles of diiferent diameters w^as not furnished 

 as was intended. 



The first experiments to be noted were those in regard to the com- 

 parison of penetrating j)ower of the siren and the whistle, the fitting up 

 of the Daboll trumpet not ha^ang been completed. The principal object 

 of this however w^as to test again the truthfulness of the indications of 

 the artificial ear in comparison with those of the natural ear. . 



An experiment was made both by means of the artificial ear on land 

 and by actually going off on the ocean in a steamer until the sounds be- 

 came inaudible to the natural ear. By the latter method the two sounds 

 ceased to be heard at the distances of six, and twelve and a half miles, 

 resi^ectively. The indications of the artifical ear gave a similar result, 

 the distance at which the sand ceased to move in one case being double 

 that of the other. In both cases the conditions of wind and weather 

 ■were apparently the same. In the case of the steamer the distance was 

 estimated by noting the interval of time between the flash of steam and 

 the i^erception of the sound. 



Comparison of the BaboU trumpet and the siren. — The pressure of the 

 hot air in the reservoir of the hot-air eugine of the trumpet was about 

 20 pounds, and that of the steam in the boiler of the siren about 75 

 pounds. These pressures are however not considered of importance in 

 these experiments, since the object was not so much to determine the 

 relative amount of motive power employed as the amount of penetrat- 

 ing power produced by these two instruments, each being one of the 

 first of its class. 



1. At distance 50 the trumpet produced a decided motion of the sand, 

 while the siren gave a similar result at distance 58. The two observa- 

 tions being made within ten minutes of each other, it may be assumed 

 that the condition of the wind was the same in the two cases, and hence 

 the numbers above given may be taken as the relative penetrating power 

 of the two instruments. 



2. Another series of experiments was instituted to determine whether a 

 high or a low note gave the greatest penetration. For this purpose the 



