402 WRITINGS OF JOSEPH HENRY, [1874 



These results illustrate very strikingly the tendency of 

 sound to spread on either side of the axis of the trumpet; 

 had the experiments been made with a more sensitive instru- 

 ment and at a greater distance the effect would have shown 

 a much greater divergency of the sound. It should be ob- 

 served however that the mouth of the trumpet in this case 

 was 36 inches, which is unusually large. 



From the experiments made near New Haven, and also 

 from those at this station, it appears that the actual amount 

 of power to produce sound of a given penetration is abso- 

 lutely less with a reed trumpet than with a locomotive 

 whistle. This fact probably finds its explanation in the cir- 

 cumstance that in each of these instruments the loudness of 

 the sound is due to the vibration of the air in the interior of 

 the trumpet and in the bell of the whistle, each of these being 

 a resounding cavity; and furthermore that in these cavities 

 the air is put in a state of sustained vibration by the undu- 

 lations of a tongue, in the one case of metal, in the otlier of 

 air; and furthermore it requires much more steam to set the 

 air in motion by the tongue of air than by the solid tongue 

 of steel, the former requiring a considerable portion of the 

 motive power to give to the current of which it consists, the 

 proper degree of stiffness (if I may use the word,) to produce 

 the necessary rapidity of oscillation. But whatever may be 

 said in regard to this supposition, it is evident in case reli- 

 able hot-air engines cannot be obtained, that the Daboll 

 trumpet may be operated by a steam-engine, although at an 

 increased cost of maintenance, but this increase we think will 

 still not be in proportion to the sound obtained in compari- 

 son with the whistle. 



