I02 SCIENCE PROGRESS 



its " height " and " depth." The only suspicious feature in the 

 theatre is said to be the sky-Hght, and the author seems to think 

 that this just misses having a serious effect because it is circular 

 and not square in plan, a proposition not easy to justify. 



The problem of designing an auditorium with satisfactory 

 acoustic properties requires for its complete solution two 

 distinct lines of investigation. In the first place, it is necessary 

 to determine quantitatively the physical conditions on which 

 loudness, reverberation, resonance, and allied phenomena 

 depend. And, secondly, the intensity which each of these 

 should have to produce conditions satisfactory for distinct 

 audition of speech and of music in its various forms must be 

 settled. 



The first of these is a purely physical question, which must 

 be capable of scientific experimental investigation, and its 

 conclusions can be disputed only on scientific grounds ; the 

 second is a matter of judgment and taste, and its conclusions 

 are convincing in proportion to the weight and unanimity of 

 the authority in which they find their source. 



The question as to what constitutes good or poor acoustics, 

 what effects are desirable in an auditorium designed for speak- 

 ing, and even more in one designed for music, is not a question 

 in physics. The question is, however, of the utmost importance, 

 for it is of little value to be able to calculate in advance of 

 construction and express numerically the acoustical quality 

 which any planned auditorium will have unless the quality 

 which is desired is also similarly capable of numerical expression. 

 On the other hand, if the owner and the architect can agree as 

 to the desired result, and if this is within the limits of possibility 

 considering all the demands on the auditorium of utility, 

 architecture, and engineering, this result can be secured with 

 certainty — or at least there need be no uncertainty as to whether 

 it will or will not be attained in the completed building. 



When a speaker delivers an address the sound proceeds 

 from him in spherical waves to the boundaries of the room, 

 unless it is absorbed on the way. At the walls it may be 

 reflected or transmitted or absorbed. In general it will suffer 

 all three kinds of treatment in relative proportions which depend 

 on the character of the walls. Hard and smooth walls will 

 reflect the major part of the sound, while porous and yielding 

 walls will reflect very little. Eventually, after successive 

 impact on different surfaces, the whole of the sound will be 

 absorbed. 



The effect of reflection is twofold. If the room is not too 

 large the first effect will be to produce the same average loud- 

 ness at different points of the room. In the case of a room 40 ft. 

 square reflections will occur at least twenty-seven times a second. 



