164 ANNUAL OF SCIENTIFIC DISCOVERY. 



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 assisting 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 wall? 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 parallel- 

 ogram, 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 flat ceiling. Mr. 

 Scott Russell strongly enforced the necessity of breaking up the surface 

 to prevent reverberation ; 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 cover the walls with beadings or mouldings. 



VISION AND SOUND. 



Prof. Stokes, in a note to a paper in the Philosophical Magazine, 

 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 source of light, giving out rays of a definite 

 refraugibility, and an absorbing medium, extinguishing rays of that 

 same refrangibility which traverse it, seems readily to admit of a 

 dynamical illustration borrowed from sound. 



We know that a stretched string which, on being struck, gives out 

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

 thrown into the same state of vibration by aerial vibrations corres- 

 ponding to the same note. Suppose, now, a portion of space to con- 

 tain a great number of such stretched strings, forming thus the ana- 

 logue of a " medium." It is evident that such a medium, on being 

 agitated, would give out the note above mentioned ; while, on the 

 other hand, if that note were sounded in air at a distance, the incident 

 vibrations would throw the strings into vibration, and consequently 

 would themselves be gradually extinguished, since otherwise there 

 would be a creation of vis viva. The optical application of this illus- 

 tration is too obvious to need comment. 



DANIELL'S GREAT WATER BAROMETER. 



A water barometer which had been constructed thirty years ago by 

 Prof. Daniell, in London, was lately removed and put up in the Crys- 

 tal Palace at Sydenham. About a foot and a half of glass having 

 been broken off the lower end of the barometer tube, Mr. Negretti 



