116 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK n. 



By carefully analysing all the causes of defect in present 

 buildings, and taking into account the laws of the propagation 

 and the reflection of sound waves, we should be able doubtless 

 to solve the difficulties of the problem. Some of these rooms fail, 

 either for want of, or an excess of, sonorousness. The form of the 

 walls or sides of the room first of all has a predominating influence. 

 Often the voice and sounds are absorbed by very considerable masses 

 of air, in which the sharp force of the sound-w r aves is lost before they 

 are able to reach the ear of the listener. Too great height of ceiling 

 or roof, too great length from the stage and side-scenes, too great 

 depth of the boxes, often hung with woollen stuffs and deadening 

 draperies, make a room dumb and at the same time little favourable 

 to the emission and to the hearing of the singer's or orator's voice, as 

 also to that of instrumental sounds. 



Rooms with Avails having a form which give to the reflected waves 

 different centres of convergence, or composed of substances which 

 send back the sound with too much promptness, have the opposite 

 defect. They have an exaggerated and intemperate sonorousness, 

 besides being very unequal ; they resound, and the listener hears 

 both direct and reflected sounds, confusion follows, if speech is in 

 question, and most disagreeable discord in the case of musical sounds. 

 * The rules to be observed to remedy these serious inconveniences 

 can only be general, or at least they are susceptible of modifications 

 according to 'the circumstances of their general Application. For the 

 most part, they are reduced to a combination of very simple acoustic 

 laws with the laws of architectural construction. 



The following is what is said touching this by M. Th. Lachez, 

 the author of a small treatise on " L' Acoiistique et Optiques des lie- 

 unions publiques" who is at the same time an architect. We will only 

 quote that part of his opinion \\hich refers to the three classes of 

 rooms to which we have referred. 



" To cause musical sounds and singing to be heard. 



"Whether the music be played in an unlimited space or in an 

 inclosure shut in on every side, it is possible that the audience may 

 see nothing in either case, and take in all the sounds, without looking 

 at the instruments which produced them. Thus to fix the place 

 where the sounds are produced, in the most convenient spot, and in 

 the most favourable circumstances, in order that the sounds should be 



