Study of Locomotive Whistles 105 



A STUDY OF LOCOMOTIVE WHISTLES. 

 Arthur L. Foley, Indiana University. 



Some two years ago the writer was employed by a railroad com- 

 pany to make a study of the whistle, bell and headlight of one of the . 

 company's locomotives that had killed a score of children in a school 

 hack at a road crossing. The driver had stopped, looked, and listened. 

 Apparently he had not seen or heard. Why? 



It is not my intention to try to answer the question why in this 

 paper. It is my purpose, however, to call attention to several ways 

 in which my experiments indicate that the efficiency of locomotive 

 whistles may be, and should be, improved. 



In the first place, the location of the whistle is bad, usually about 

 as bad as could be found unless it were placed inside the cab or 

 underneath the locomotive. It is always placed behind the smoke stack, 

 usually behind one or more domes and the bell, and frequently im- 

 mediately behind or at the side of pop-off valves, or other accessories 

 mounted on the top of the boiler. All of us know that if we wish to 

 shout to some one at a considerable distance that we turn toward the 

 listener so that the sound will be projected initially in that direction. 

 All of us know that we can be heard at a greater distance if we do 

 not stand behind a lamp post or a tree when we shout. All of us know 

 that the roar of an aeroplane engine as it passes over us comes and 

 goes, sometimes being very loud and sometimes barely audible, and that 

 the variation in the sound intensity is due to the varying air currents 

 and temperature strata through which the sound must pass to reach 

 the ear. Notwithstanding all this, we continue to locate locomotive 

 whistles from the standpoint of convenience only, with no thought of 

 a possible connection between the whistle's location and its efficiency 

 in doing the only thing it is expected to do — to make as much noise 

 as possible along the track ahead of the locomotive, and as little as 

 possible in directions where it is not only not needed but is usually a 

 nuisance. 



When the whistle is placed behind the smoke stack, dome, etc., all 

 these objects reflect the energy of the portion of the sound wave that 

 falls upon them. Since a sound wave is long compared to 

 a light wave, the sound shadows thus produced are not comparable in 

 density or definiteness to the light shadows that would result were the 

 whistle replaced by the head light. Nevertheless, there are sound 

 shadows of more or less intensity, depending on the size of the object 

 casting them and on its distance from the sound source; in other words, 

 depending on the solid angle of the object as seen from the sound source. 

 Where the distance is small and the angle large, as when a whistle is 

 mounted very near a dome or an escape valve — (immediately behind or 

 at one side in some recent practice) the intensity of the sound ahead 

 of the locomotive is decreased and at the side or rear increased over 

 what it would be were the whistle mounted in front of the smoke stack. 



"Proc. Ind. Acad. Sci., vol. 33, 1923 (1924)." 



