152 YEAR-BOOK OF FACTS. 



which the possibility of supplying a sufficient degree of force in its 

 agencies may oppose. Hence it is probable that there is no sound 

 which is propagated faster than a thunder- clap, the genesis of which 

 by the electric discharge being extremely violent and almost instan- 

 taneous, is accompanied by a large development of heat. 



If the theory here advanced be true, the report of fire-arms should 

 travel faster than the human voice ; and the crash of thunder faster 

 than the report of a cannon. 



ACOUSTICS IN BUILDING. 



A paper on Acoustics has been recently read at the Royal 

 Institute of British Architects, by Mr. T. R. Smith. This gentleman, 

 after referring to the experiments of M. Biot on the transmission of 

 sound through a pipe 1000 yards long, through which a whisper was 

 distinctly audible, and to the curious exception discovered by Mr. 

 Scott Russell to the ordinary law of reflection of sound when the 

 sonorous vibrations strike against a reflecting surface at an acute 

 angle — maintained that in order to combine reflection and resonance 

 in the construction of a building there should be an inclined surface 

 above the head of the speaker, to reflect the sound down upon the 

 audience ; the walls should be covered with wood, and there should 

 be a space above the ceiling and under the floor. But in thus assist- 

 ing the transmission of sound great care should be taken to prevent 

 echoes. To avoid echoes by reflection the head of the speaker should 

 be near the ceiling, or a sounding-board should be placed above him, 

 so that the sound may be propelled onward ; and the surface of the 

 walls should be broken by pillars or draperies, particularly at the 

 end. The vibrations caused by resonance should also be prevented 

 by draperies, or by breaking up the surface by projections. Mr. 

 Smith considered a short parallelogram, with a semi-circular end, as 

 the form best adapted for hearing : the speaker being advanced to a 

 forward position among the audience. The most difficult of all 

 buildings for hearing a speaker, he said, are parallelograms of four 

 flat sides, and with a high Hat ceiling. Mr. Scott Russell strongly 

 enforced the necessity of breaking up the surface to prevent reverbe- 

 ration ; and, alluding to the different effects of the transmission of 

 sound in full and in empty rooms, he observed that the best possible 

 means of making sounds distinctly audible in large rooms is to fill 

 the walls with beads. 



VISION AND SOUND. 

 PBOF. STOKES, in a note to a paper in the Philotopkical }f<t<jazinc, 

 No. 126, observes: — The remarkable phenomenon discovered by 

 Foucault, and rediscovered and extended by Kirchhoff, that a body 

 may be at the same time a BOUroe of light giving out rays of a defi- 

 nite refrangibility, and an absorbing medium extinguishing rays of 

 that same refrangibility which trai ms r eta i l; to admit of 



a dynamical illustration borrowed from sound. 



VVe know that a stretched string which on being struck gives out 

 a certain note (suppose its fundamental note) is capable of being 



