354 



i)K. K(i:ni(i s kivskakches on 



from wliicli wind issues, the inaxiimini (lisi)laceinent of air will result 

 when the slit is least covered, or wheu the point of greatest depression 

 of the curve crosses the front of the slit. The negative ordinates of the 

 curve correspond therefore ai)proxiinateIy to condensations. Air is 



Fig. 7. 



now being supplied to the slits ; and when I open one or other of 

 the valves which control the air passages, you hear one or other of the 

 sounds. It must be audible to everyone present that the sonnd is 

 louder and more forcible with a difference of phase of \ than in any 

 other case, that produced with ^ difference being gentle and soft in tone, 

 whilst the curves of phase and ^ yield tones of intermediate quality. 

 Dr. Kcenig found that if he merely combined together in various phases 

 a note and its octave (which was indeed the instance examined by me 

 binanrally in 1876), the loudest resultant sound is given when the phase 

 difference of the combination is ^, and the mildest when it is ^. 



Returning to Fig. 6, in the second line are shown the curves which 

 result from the superposition of the odd members only of a harmonic 

 series of decreasing am[)litude. On comparing together the curves of 

 the four separate phases, it is seen that the form is identical for phases 

 and i, which sho\v rounded waves, whilst for phases ^ and '} the lbrn)S 

 are also identical, but with sharply angular outline. These two varie- 

 ties of curve are set out on the two edges of the highest metallic cir- 

 cumference in the apparatus depicted in Fig. 7. The angular waves are 

 found to yiebl a louder and more strident tone than the rounded waves, 

 though, according to von Uelmholtz, their tones should be aiike. 



A much more elaborate form of compound wave siren was constructed 

 by Dr. K^nig for the synthetic study of these phase relations. Upon 

 a single axis, one behind the other, is mounted a series of 10 brass disks, 



