132 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



to the case of an observer moving upon a locomotive, with 

 a velocity of a hundred feet per second, and listening to a 

 sound whose origin moves at the same rate toward him, he 

 finds the observed sound 0.8 times as loud as when both are 

 at rest. A method is also explained by him, showing the 

 possibility of testing his conclusions by experiments on the 

 heat received and sent by moving bodies. Poggendorff 

 Annalen, CLIL, 535. 



THE THEORY OF RESONATORS. 



Lord Rayleigh contributes an extract from a forthcom- 

 ing work by himself on acoustics, in which he submits a 

 new theory of the action of resonators, and opposes em- 

 phatically the general statement that a resonator augments 

 the body of sound by offering a column of air which is ca- 

 pable of vibrating in unison with the original sounding 

 body. The exceptions to this rule, he thinks, are very im- 

 portant in a theoretical point of view ; and he prefers to re- 

 verse the statement, and to say that the neighborhood of a 

 resonator in unison with a sounding body diminishes the 

 loudness of the latter. The resonator, in fact, instead of 

 augmenting the effect of a source of sound, annuls it alto- 

 gether, so far as external space is concerned, by absorbing 

 the condensations and rarefactions into itself. Phil. 31ag- 

 azhie, p. 419. 



VIBRATION OF MEMBRANES. 







In a paper read before the London Mathematical Society, 

 Lord Rayleigh demonstrates the theorem that an increase in 

 the dimensions of a vibrating system is attended by a rise in 

 pitch. For instance, if the system consists of a uniformly 

 stretched membrane, with a fixed edge, it follows that any 

 contraction of the boundaries must cause an elevation of 

 pitch. If the membrane be uniform, of given density and 

 given tension, the frequency of vibration is a function of the 

 size and form ; and if the form is invariable, the frequency 

 varies as the linear dimension. The pitch of the vibrations 

 of a regular polygon is intermediate between those of the 

 inscribed and circumscribed circles. When the area of the 

 membrane is given, it is easy to see that any projecting cor- 

 ners tend to raise the pitch, thus among rectangles of a given 



