106 



Proceedings of Indiana Academy of Science 



That this effect is not of negligible import is proven by the following 

 observations : 



In figure 1 the ten points on the broken line curve give the relative 

 intensity of sound as measured v^^ith a Rayleigh disk in the ten indicated 

 directions from the whistle or of a locomotive L standing on the track 

 T T. On the first day the observations were attempted a Webster 

 phonometer was used to measure the sound intensity. On account of 

 the extreme sensitiveness of this instrument to small changes of pitch 

 it was not satisfactory for the work in hand. It was therefore with 

 little regret that the writer was foi'ced to discontinue his experiments 



Fig. 1. Sound intensity about a locomotive whistle. 1-10 are the ten points of 

 measurements ; L the locomotive ; W the location of the whistle ; TT the track. 



that day on the demand of some one to whom the noise of the whistle 

 was objectionable. 



Before undertaking the experiment a second time the writer experi- 

 mented on different forms of Rayleigh disks. The instrument in the 

 form finally chosen is less sensitive than a tuned Webster phonometer, 

 but has a much wider range through which the pitch of the sound may 

 change without seriously affecting the instrument's sensitivity. 



The intensities shown in figure 1 were measured in the ten direc- 

 tions shown, at a uniform distance of 1200 feet from the whistle. In- 

 stead of moving the observing station the locomotive was placed on a 

 turn table and the observing station located permanently at the side 

 of the track 1200 feet from the turn table. Then the locomotive was 



