ACOUSTIC ARCHITECTURE. 457 



that hot and cold currents do not readily mix, but fill the whole audi- 

 torium with alternations, continually varying in temperature and there- 

 fore in density and relative motion. 



The proper solution of the problem is to admit the air in large 

 volume, and at the proper temperature, at one side of the auditorium, 

 carry it bodily across the room in one large mass as nearly as may be 

 without break of homogeneity, and exhaust it at the other side. Or it 

 may be introduced through a perforated floor and rise to be exhausted 

 at the roof. This plan has been tried with success ; the air, being first 

 brought to the proper temperature in the basement, passes up through 

 myriads of gimlet-holes, and is exhausted at the ceiling by means of 

 numerous openings connected with a high chimney or other means of 

 producing an exhaust. 



An example of the first method is shown in the Baltimore Academy 

 of Music, where the author was able to make some experiments to 

 determine how far acoustic properties were actually dependent upon 

 the condition of the air. The ventilation of the house is arranged as 

 follows : The whole supply of fresh air is admitted at the back of the 

 stage, is then warmed, then crosses the stage horizontally, passes 

 through the proscenium, and then, somewhat diagonally toward the 

 roof, across the auditorium, in one grand volume and with gentle mo- 

 tion, so as to almost entirely prevent the formation of minor air-cur- 

 rents. It is exhausted partially by an outlet in the roof, and partly 

 by numerous registers in the ceilings of the galleries. From this cen- 

 tral outlet and from the large flues of the registers, the air passes into 

 the ventilating tower over the great chandelier, which supplies, in its 

 heat, a part of the motive power of the circulation. It is further ex- 

 pelled from the tower by means of properly constructed ventilators. 

 The acoustic properties of this house are universally agreed to be very 

 superior. 



The experiment made by the author consisted in stationing ob- 

 servers in various parts of the house while the performance was going 

 on, with directions to note, at intervals during the evening, the readi- 

 ness with which they could hear what was said on the stage. The ob- 

 servers were ignorant of the experiment to be tried. Observers A and 

 B were stationed in the first, and C and D in the second balcony, from 

 8 to 10 one evening, when Neilson was playing "Rosalind." At 8.50 

 the ventilators were closed, so as to interrupt the normal circulation 

 of air ; and the doors into the lobbies, and thence into the street, were 

 thrown open, that counter-currents might be established. At 9.20 the 

 doors were closed, and the ventilators set right. The testimony of the 

 observers was : 



A (first balcony). 8 to nearly 9, good ; for about half an hour, 

 bad ; afterward much better. 



B (first balcony).-^8 to 9, good ; 9 to 9.30, bad ; 9.30 to 10, good. 

 Strong current of air felt from door a little before 9. 



