398 WRITINGS OF JOSEPH HENRY. [1874 



seen hereafter. General James C. Duane has also made ex- 

 periments on whistles of different diameters, of which the 

 result will be given. 



Another consideration in regard to the same matter is that 

 of the amplitude of the oscillations of the tongue or steel 

 reed in its excursion in producing the sound ; the time of 

 oscillation (that is the pitch) remaining the same, the ampli- 

 tude will depend upon the elasticity of the reed, the power 

 to surmount which will again depend upon the pressure of 

 steam in the boiler, and hence we might infer that an 

 increase of pressure in the boiler with an increase of the 

 elasticity of the reed, everything else being the same, would 

 produce an increase in penetrating power. From the gen- 

 eral analogy of mechanical eflects produced by motive power 

 we maj' denote the effect upon the ear by the expression 

 mif^, in which m expresses the mass or quantity of air in 

 motion, and v the velocitj' of the particles in vibration. 



If this be the expression for the effect upon the ear, it is 

 evident that in case of a very high note the amplitude of 

 the vibration must be so small that the effect would approxi- 

 mate that of a continued pressure rather than that of dis- 

 tinct alternations of pressure, giving a vibrating motion to 

 the drum of the ear. 



4. Experiments were next made to determine the pene- 

 trating power in the case of the siren under different pressures 

 of steam in the boiler. The experiments commenced with a 

 pressure of 100 pounds. The pressure at each blast was 

 noted b}^ two observers, and to compare these pressures with 

 the indications of the sand, the time of the blasts was also 

 noted. 



The following are the results : 



p Kelative distances at which 



iressure. ^j^^ sund ceased to move. 



100 61 



90 59 



80 58 



70 .__ 57 



60 57 



50 5G 



40 55 



30 53 



20 51 



