Whistle Experiments 193 



The shape of the external horn is not necessarily conical, nor is it 

 entirely arbitrary. It is determined by the use to which the horn is to 

 be put, to its length, aperture, and small end diameter, to the distance 

 to the sound source, to the extent it is desired to make use of the horn 

 as a sound resonator, and to the pitch and quality of the sound to be 

 amplified or condensed. 



Figure 2 shows both horns, H and S of the same shape. This is 

 not always the most efficient design. The shape of the outer horn having 

 been decided upon, the inner horns are so shaped as to condense the 

 maximum amount of energy at the small end. They are supported by 

 radial strips of sheet metal placed with the plane of the strips parallel 

 with the common axis of the horns, in order to give minimum inter- 

 ference to the passage of sound waves through the system. 



The writer is still experimenting with multiple horns of different 

 designs, in order to determine the one having the maximum efficiency. 

 An account of this work, with data, will be published later. 



LOCOMOTIVE WHISTLE EXPERIMENTS. 



Arthur L. Foley, Indiana University. 



A study of the amount of steam, and consequently the amount of 

 coal, required to blow an ordinary locomotive whistle, the probable aver- 

 age time per day the whistle is blown, and the total number of loco- 

 motives in use, convinces me that we "pay dearly for the whistle". Is 

 it not possible to reduce the cost and the coal waste? 



In the first place, it would seem that the position of the whistle 

 is bad. It is almost always behind the smoke stack, and frequently 

 behind or at the side of the steam dome, bell or sand box. Sound shad- 

 ows are not pronounced like light shadows. Nevertheless sound shad- 

 ows actually exist. The intensity of the sound along the track in front 

 of a locomotive is certainly somewhat lessened by placing the whistle 

 behind the smoke stack or other objects. But it is much further re- 

 duced by the hot gases coming from the smoke stack, which act like a 

 dispersing cylindrical lens. Moreover, the currents of hot air about the 

 walls of the smoke stack and rising from the boiler are both absorbing 

 and dissipating for sound energy. That such conditions are undesirable 

 can not be questioned. The question concerns the magnitude of their 

 effect. Is the reduction in the intensity of the sound along the track 

 sufficient to warrant placing the whistle in front of the locomotive smoke 

 stack, as is the case with the headlight? 



A second question. Can one devise a sound reflector that will in- 

 crease the sound intensity along the track where it is needed and de- 

 crease it in other directions where it is not only not needed, but is 

 usually a nuisance? 



It has been argued that sound waves are relatively so long that 

 a reflector of ordinary size would have little or no effect. Certainly 

 we should not expect results anything comparable to what we have in 



13—25870 



