VI. RESONATORS. 161 



735a. Interference Apparatus, by Jamin. 



M. J. Duboscq, Paris. 



735b. Interference Apparatus. Professor W. F. Barrett. 



V. ABSORPTION, REFLECTION, AND REFRACTION. 



736. Apparatus for showing Approach caused by 

 Vibration. Frederick Guthrie, F.R.S. 



A suspended card or mass of cotton wool, or an air ball floating in water, 

 approaches a resonant fork ; and the latter, when free to move, is also urged 

 towards neighbouring matter. 



737. Apparatus for showing the Expansion of Gases 

 by Sound. Frederick Guthrie, F.R.S. 



One prong of a tuning fork is enclosed, air-tight, in a glass tube provided 

 with a capillary exit tube, in which water stands at a certain height. On 

 bowing the free prong of the fork the water level is seen to fall about a quarter 

 of an inch. 



738. Apparatus for the Reflection of Sound by heated 

 air and vapours. Professor Tyndall, F.R.S. 



Sound of high pitch from a vibrating reed is passed through a long rectan- 

 gular chamber, and caused to agitate a sensitive flame. Air, saturated with the 

 vapour of a volatile liquid, is gently driven through six narrow openings into 

 the chamber, at right angles to the direction of the sound. The atmosphere* 

 within the chamber is thus immediately rendered heterogeneous, and the 

 sound waves being reflected, the agitated flame is rapidly stilled. The removal 

 of the heterogeneous medium instantly restores the flame to its former 

 agitation. 



For the action of heated air, the rectangular chamber is turned upside 

 down upon its support, and the heated air from six gas jets allowed to stream 

 in through six narrow openings across the sound waves. The air thus 

 rendered heterogeneous has the effect of immediately rendering the sensitive 

 flame quiescent. Phil. Trans., 1874. 



739. Diagrams and Apparatus illustrating the reflection 

 and refraction of sound-bearing waves, as exhibited to a class by 

 means of a sensitive flame. Prof- f?. F. Barrett, Dublin* 



The arrangement shows a suitable source of sound, a good form of gas 

 pillar for yielding a tranquil flow of gas to the burner, and the best shape 

 and size of steatite burner for the flame, together with a useful form of gas- 

 holder for giving steady pressure of gas larger than that usually given by the 

 street mains. 



VI. RESONATORS. 



740. Resonator of adjustable pitch. Lord Rayleigh. 



Resonator, whose pitch can be rapidly adjusted to the various notes of a 

 harmonic scale A 6 , a 6 , e 6 , a 16 , c 11 . The smallest hole is made first and ad- 

 justed until the resonator responds a 6 . The second hole is then made and 



39508. L 



