390 PROCEEDINGS OF THE AMERICAN ACADEMY. 



sound intensity. The irregularities of the curve were actually exist- 

 ent in the interference system and were verified by a repetition of the 

 experiment. 



In the above curve the current obtained at the best of the maxima 

 was 3.30 X Kr'' ampere. When it is noted that this was at a distance 

 of 15 meters from the source of sound, it will be seen that the receiving 

 apparatus possesses quite remarkable sensitiveness. Of course, too 

 much importance must not be given to the distance from the source 

 as a determining factor of the intensity, for, as will soon appear, this 

 particular position, accidentally chosen, in the rear of the room was 

 a position in which the sound was more intense than at many places 

 much nearer to the source. However, even with a galvanometer of 

 only moderate sensitiveness it was possible to extend the investigation 

 satisfactorily to any part of the room. Curves of results at two other 

 positions in the room are discussed below. 



The question arises, how may we determine the exact region of 

 space to which the indications belong'? In Curve 1 of Figure 8 a 

 maximum was found when the opening of the receiver was 5 cm. from 

 the wall. Is the maximum of sound vibration at the opening of the 

 cone, and, therefore, 5 cm. from the wall or is it inside the cone or 

 outside the cone ? Can we locate its exact position 1 In attempting to 

 answer these questions it was decided to try the effect of reversing the 

 telephone so that the opening pointed away from the wail. With the 

 telephone thus reversed Curve 5 of Figure 8 was obtained. Unfortu- 

 nately, on account of the size of the telephone and cone, it was not 

 possible to extend the observations to points nearer the wall than 

 40 cm. The distance measurements for this curve were also made 

 from the wall to the opening of the cone. By a comparison of this 

 curve with Curve 4 we may get some evidence of the location in space 

 of the sound vibration. 



The two maxima of Curve 5 probably correspond respectively to the 

 two right hand maxima of Curve 4, as is evidenced by their distance 

 apart, and their relative amplitudes, and by the distance apart of the 

 minima of Curve 5 as compared with the minima at 75 and 108 of 

 Curve 4. Now it is seen by inspection that these two curves would be 

 brought into coincidence as to location of maxima and minima, if, 

 instead of having measured from the wall to the opening of the cone 

 of the telephone, we had measured to a point 5.7 cm. outside of the 

 cone ; that is to say, the indications of the galvanometer are indica- 

 tions as to the relative amplitude of the sound vibration at a point b.l cm. 

 outside of the opening of the sound-collecting cone. 



While this reasoning is not entirely conclusive without further 



