476 RESEARCHES IN SOUND, 



and the artificial ear at the other, substituting fine shot instead of sand. 



The experiments with the siren however indicate the fact that neither 

 the highest nor the lowest pitch of an instrument gives the greatest pen- 

 etrating power, but one of a medium character. 



Another element of importance in the construction of these instru- 

 ments is the volume of sound. To illustrate this, it may be mentioned 

 that a harpsichord- wire stretched between two strings of India rubber, 

 when made to vibrate by means of a fiddle-bow, gives scarcely any 

 appreciable sound. We attribute this to the want of quantity in the 

 aerial wave; for if the same wire be stretched over a sounding-board 

 having a wide area, the effect will be a comparatively loud sound, but 

 of less duration, with a given impulse. It was therefore suggested that 

 the width of the reed in the Daboll trumpet, the form and size of the 

 holes in the disk of the siren, and the circumference of the vibrating 

 sheet of air issuing from the circular orifice of the whistle, would affect 

 the power of the sound. The only means of testing this suggestion is 

 by using reeds of difl'erent widths, sirens with disks of different-shaped 

 openings, and whistles of different diameters. In conformity with this 

 view, Mr. Brown has made a series of empirical experiments with open- 

 ings of different forms, which have greatly improved the operation of 

 the siren, while Mr. Wilcox has experimented on several forms of reeds, 

 of which the following is the result : 



The best reed obtained was 2^ inches wide, 8 inches long in the xi- 

 brating part, f inch thick at the butt, and 4 inch thick at the free end. 

 This sounded at a pressure of from 20 to 30 pounds. The thinner reeds 

 gave a sound at a less pressure, from 5 to 10 pounds, the thicker at from 

 20 to 30 pounds. A reed 8i inches long in the vibrating part, 1 inch thick 

 at the butt, f inch thick at the end, and 3 inches wide, did not begin to 

 sound until a pressure of 80 pounds was reached, then gave a sound of 

 a dull character. Another reed of the same width, § inch thick at the 

 butt, and -^,^ inch at the end, and same length, gave a sound at 75 pounds 

 pressure, but still dull and of little penetrating power. These reeds 

 were evidently too heavy in proportion to their elasticity. These were 

 made without the addition of a trumpet, and therefore to produce the 

 best result when used with a trumpet, the latter must be increased or 

 diminished in length until its natural vibratioDS are in harmony with 

 those of the former, as will be seen hereafter. General Duane has also 

 made experiments on whistles of different diameters, of which the result 

 will be given. 



Another consideration in regard to the same matter is that of the am- 

 plitude of the oscillations of the tongue or steel reed in its excursion in 

 producing the sound; the time of oscillation remaining the same, that 

 is, the pitch, the amplitude will depend upon the elasticity of the reed, 

 the ijower to sui-mount which will again depend upon the pressure of 

 steam in the boiler, and hence we might infer that an increase of pies- 



