420 WRITINGS OF JOSEPH HENRY, [1856 



pose. It was found impossible however to construct a room 

 on acoustic principles in this part of the building, which was 

 necessarily occupied by two rows of columns. The only 

 suitable place which could be found was therefore on the 

 second floor. The main building is two hundred feet long 

 and fifty feet wide; but by placing the lecture room in the 

 middle of the story a greater width was obtained by means 

 of the projecting towers. 



The main gallery is in the form of a horse-shoe occu- 

 pying three sides of the room. The speaker's platform is 

 placed between two oblique walls. The corners of the room 

 which are cut off by these walls afford recesses for the stairs 

 into the galleries. The opposite corners are also partitioned 

 off so as to afford recesses for the same purpose. 



The general appearance of the room is somewhat fan- 

 shaped, and the speaker is placed in the mouth as it were 

 of an immense trumpet. The sound directly from his voice 

 and that from reflection immediately behind him is thrown 

 forward upon the audience; and as the difference of distance 

 travelled by the two rays is much within the limit of per- 

 ceptibility no confusion is produced by direct and reflected 

 sound. 



Again, on account of the oblique walls behind the speaker 

 and the multitude of surfaces, including the gallery, pillars, 

 stair-screens, &c., as well as the audience, directly in front, 

 all reverberation is stopped. 



The walls behind the speaker are composed of lath and 

 plaster, and therefore have a tendency to give a more intense 

 though less prolonged sound than if of solid masonry. 

 They are also intended for exhibiting drawings to the best 

 advantage. 



The seats are arranged in curves and were intended to rise 

 in accordance with the panoptic curve, originally proposed by 

 Professor Bache, which enables each individual to see over 

 the head of the person immediately in front of him. The 

 original Jorm of the room however did not allow of this 

 intention being fully realized, and therefore the rise is some- 

 what less than the curve would indicate. 



