110 



Proceedings of Indiana Academy of Science 



one hemisphere, as does the megaphone; but in addition it turns back 

 those that start in the other hemisphere. 



To determine whether or not a reflector of moderate size could be 

 made to exert any considerable directive force on the sound from a 

 locomotive whistle, the chime whistle previously described in this paper 

 was placed in a parabolic reflector, as shown in cross section in figure 4, 

 in which all dimensions are to the same scale. The whistle was 6.5 

 inches in diameter and the aperture of the reflector 28 inches. The 

 reflector was made of plaster paris P cast in a wooden box B. Wooden 

 strips S were nailed in the box in the manner indicated in the drawing 

 to economize on plaster and lessen the weight. The box was mounted on 



Fitr. 4. Transvorsf section of a locomotive chime whistle, and a lonKitutlinal section 

 of whistle mounted in a modified paiabolic reflector. See text for explanation. 



castors so that it could be turned on a platform about six feet in diam- 

 eter and eight feet high. The steam line projected vertically through a 

 hole in the center of the platform and was connected with a union joint 

 to the valve end V of the whistle. This permitted the reflector and 

 whistle to be rotated so that their common axis was in any desired 

 horizontal direction. 



The shape of the plaster paris surface of the reflector was obtained 

 as follows: with a focal point on one edge of a board and the edge the 

 axis of a parabola, a curve was drawn on the board and the half 

 parabola sawed out. With the board radial and its straight edge held 

 against the whistle the board was moved around the whistle and the 

 soft plaster paris "wiped" into position. The focus of such a reflector, 



