358 PHYSICS. 



distinct soimds. In carefully dried air only the feeblest sound was 

 heard, but a puff of breath instantly restored its power to absorb. 

 Many beautiful and striking experiments are described in the paper. 

 {ProG. Roy. Soc, January 13, 1881, xxxi, 307 ; Nature, February, 1881, 

 xxiii, 374.) 



Mercadier has studied photophone phenomena with great ability, 

 and has given the name radiophony to the general subject. In the first 

 part of his memoir he describes his apparatus, and, from the results ob- 

 tained with it, concludes : (1) that radiophony does not appear to be an 

 effect produced by the mass of the receiving plate vibrating transversely 

 as a whole like an ordinary vibrating plate; (2) that the nature of the 

 molecules of the receiver and their mode of aggregation does not appear 

 to play a predominant part in the production of sounds ; (3) that the 

 radiophonic phenomena seem to result principally from an action exerted 

 at the surface of the receiver ; (4) that radiophonic sounds result from 

 the direct action of the radiations upon the receiver ; and (5) the radio- 

 phonic effects are produced principally by red and ultra-red rays; that 

 is to say, by rays which consist of long waves.* In the second part of 

 Ma paper Mercadier gives the experimental evidence that the substance 

 in which the vibration is produced is the layer of air in contact with the 

 walls of the receivers. Tne receiver used is a glass tube, oi)en or not, at 

 one end, and the other connected by a tube of rubber with a small 

 acoustic cornet. Within the tube is a semi-cylinder of some flexible 

 material, paper, mica, copper, zinc, iDlatinum, aluminum, etc., smoked 

 on both sides. Since the sound is the same, whatever the material, the 

 conclusion is obvious that it is the air condensed by the lampblack 

 which vibrates. He says : The layer of air condensed on the walls of 

 the receiver, especially when they are smoked or covered with a sub- 

 stance highly absorbent for heat, is alternately heated and cooled by 

 the intermittent radiations. From this, periodical and regular dilatations 

 and condensations take place and communicate a vibratory motion to 

 the neighboring gaseous layers, which, moreover, may themselves also 

 vibrate directly under the same influence. If a long tube of glass be 

 taken, furnished with a piston at the end of a rod, a piece of smoked 

 mica be placed in it^ and the other end be connected with a cornet, then 

 whenever an intermittent beam falls on the mica a sound is heard, which 

 may be made a maximum by moving the piston. Further motion shows 

 a second and a third maximum, thus discovering the nodes in the vi- 

 brating air column. This apparatus the author calls a thermophone. 

 The tube receiver, closed at the lower end, is excellent for experiments 

 upon gases and vapors, in which, however, the author was anticipated 

 by Tyndall. In the third paper the means which Mercadier used for 

 the production of singing and speech are described. This was presented 

 to the French Academy the same day that Bell read his memoir on the 

 same subject to the National Academy. {J. Phys., February, April, 

 June, 1881, x, 53, 147, 234; Nature, February, 1881, xxiii, 360.) 



