and Distribution of Sound, 295 



different kind of apparatus. As matters stand, it seems to 

 l)e generally admitted that the instruments nsing great power 

 are not proportionally effective. 



If, as I incline to believe, a large proportion of the power 

 applied to important instruments is not converted into 

 sound, there should be an opening for reducing the very 

 large demands now made. We have to consider what 

 l)ecomes of the power wasted. I have long thought that it 

 is spent in the eddies consequent upon the passage of the 

 air through the comparatively narrow ports of the siren, and 

 in this opinion my friend Sir 0. Lodge, with whom I have 

 recently had an opportunity of discussing the matter, concurs. 

 If indeed it were a question of steady flow, one might pro- 

 nounce with certainty that a great improvement would ensue 

 from a better shaping of the passages, which on the down- 

 stream-side should cone out gradually from the narrowest 

 place. And although the intermittent character of the 

 ^stream is an important element, this conclusion can hardly 

 he altogether disturbed. The advantage of an enlargement 

 of the ports themselves should also be kept in sight. 



The conical trumpets at present employed must act to 

 some extent as resonators, so that the precise relation of 

 the pitch or speed of the siren to the trumpet cannot be a 

 matter of indifference. Although the relation in question 

 is liable to be disturbed by changes of temperature, it would 

 appear that a better adjustment than is feasible with the 

 present governors should be arrived at. To effect this an 

 instrument capable of indicating the vigour of the vibration 

 within the trumpet, as the speed of the siren varies, would be 

 useful. 



Vibration Indicator. 



Experiments that I have tried appear to prove that the 

 problem above proposed can be solved in a very simple 

 manner. The principle is that of the unsymmetrical forma- 

 tion of jets when an alternating air-current flows through 

 an aperture coned upon one side. An experiment given in 

 ' Theory of Sound/ § 322, may be quoted in illustration : — 

 " When experimenting with one of Konig's brass resonators 

 of pitch c'^ I noticed that when the corresponding fork, 

 strongly excited, was held to the mouth, a wind of con- 

 siderable force issued from the nipple at the opposite side. 

 This effect may rise to such intensity as to blow out a candle 

 upon whose wick the stream is directed .... Closer examina- 

 tion revealed the fact that at the sides of the nipple the 

 outward flowing stream was replaced by one in the opposite 



