Study of Locomotive Whistles 



111 



if the term focus is permissible, is therefore a circle, and not a point. 

 The focus of any particular portion of the parabolic surface is the 

 nearest point on the focal circle. This focal circle was intended to 

 be coincident with the cylindrical sound source — the cylindrical steam 

 jet, at J, J. The length of the steam jet (the distance from the open- 

 ing to the lip) was two inches. There is a question as to what portion 

 of the jet should be used, or whether some point beyond the lip should 

 be used, as a focal point in adjusting the whistle in the reflector. Ex- 

 periments were made with the whistle in one position only, quite likely 



Fig. 5. 

 reflector. 



Sound intensity about a locomotive whistle mounted in a modified parabolic 



not the position to give the reflector the highest possible efficiency. 

 Nevertheless, the action of the reflector was quite marked. 



The curve in figure 5 gives the relative intensity of the sound in 

 the 12 directions indicated by the radial lines. The dissymmetry of the 

 curve with respect to the axis in direction 1 is doubtless due to the 

 fact shown in the figure that the whistle was so placed in the reflector 

 that the lower pitched and louder tone was produced on the side of 

 the axis toward direction 2, while the higher and less intense tone was 

 produced on the other side of the axis, in direction 12. Notwithstanding 

 this dissymmetry the curve clearly shows a sound intensity in the 

 direction of the axis of the reflector double that at right angles to the 

 axis and three times that to the rear. 



