116 Effect of the Motion of the Air within an Auditorium. 



B. Right balcony — 8.45 to 9.15, sound was dead; 9.15 to 

 10, decidedly better. 



C. Left balcony — 8 to 8.40, good; 8.40 to 9.15, confused; 

 9.15 to 10, good. 



D. Over stage — 8 to 8.30, good ; 8.30 to 9, strong draught, 

 hearing better; 9.10, draught disappeared. 



An examination of this Table shows that the observers in 

 the auditorium found a period of half an hour's duration when 

 the sound was not so plain as it had been before, or was after. 

 This time was of the same length, but from 10 to 15 minutes 

 later than the period of interruption of the ventilation ; but 

 some time is, of course, necessary for the air-currents to form, 

 or, being formed, for them to be destroyed. 



The observer (D) over the stage, however, found the hear- 

 ing better during the half hour of interruption ; and this is 

 exactly what would be expected, for the interruption of the 

 current of air through the auditorium causes it instead to rise 

 directly over the stage into the large space in which hangs 

 the scenery, and thence out of the building. 



During ISTeilson's performance of " Rosalind," observers A 

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

 balcony from 8 to 10 p.m. At 8.50 o'clock the ventilators 

 were closed and the lobby doors, together with those leading 

 from the lobby to the street, were thrown open. 



Thistle-balls let loose from the balconies showed currents of 

 air coming in at the doors and crossing the auditorium towards 

 the stage. At 9.20 the doors were closed and ventilating- 

 valves set aright. The testimony of the observers was as 

 follows : — 



A. First balcony — 8 to nearly 9, good ; for about an hour, 

 bad ; afterwards, 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 the door a little 

 before 9. 



C. Second balcony— 8 to 8.50, good; 8.50 to 9.20, bad; 

 9.20 to 10, good. 



D. Second balcony — 8 to about 9, good ; 9 to 9.20, bad ; 

 9.20 to 10, good. 



In the foregoing paper we have studied the effects of air- 

 currents upon the acoustic qualities of an auditorium. That 

 this is only one of the factors on which success depends the 

 author knows full well ; and experiments are now in progress 

 upon some of the other causes which modify the acoustic pro- 

 perties of churches, theatres, and halls. 



These, however, have been in part studied before, while the 

 above researches are believed to be entirely new. 



