118 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK. n. 



" To cause the speech of an orator to be heard. 



" In this case, if not necessary, it is at least of great utility, to 

 inclose the audience and speaker in a space shut in by walls ; and, 

 according as this space is more or less extensive, the speech will be 

 more or less perceptible to a certain number of people. An inclosed 

 space has not only the advantage of being protected from all ex- 

 traneous sounds, and from atmospheric inclemency ; but it ought both 

 to increase the sonorous intensity of the voice and to destroy the 

 resonance which takes place in consequence of the repercussion of 

 the waves ; the dimensions of the space and its volume, determine 

 the acoustic means to use." 



The arrangement of the auditors relatively to the sound-focus has 

 much to do with the qualities of a room in an acoustic point of view. 

 Generally, a series of seals arranged in a half circle with respect to 

 the focus, orchestra, or tribune, allowing a normal view, or at least 

 that the sounds shall be received directly, is preferable, provided 

 that the line of these seats be gradually inclined above the horizontal 

 plane along which the sonorous waves proceed. 



In theatres, where we have both orchestra and stage, and where 

 seeing must be considered as well as hearing, the conditions of the 

 problem are more complex. They are still more so, as the architect is 

 obliged to take into account traditions, customs, and routine. 



