ADVANCEMENT OF SCIENCE. 139 



ascertained. But since the ear does not readily judge of the difference of direc- 

 tion of two sounds emanating from the same source, and since two rays do not 

 confuse the impression which they produce upon the ear, though they arrive by 

 very different routes, provided they are within the limit of perceptibility, we 

 may therefore conclude that the indistinctness produced by refraction is compara- 

 tively little. Professor Bache and myself could perceive no difference indistinct- 

 ness in hearing from rays of sound passing over a chandelier of the largest size, 

 in which a large number of gas jets were in full combustion. The fact of disturb- 

 ance from this cause, however, if any exist, may best be determined by the experi- 

 ment with a parabolic mirror and the hearing trumpet before described. 



These researches may be much extended; they open a field of investigation 

 equally interesting to the lover of abstract science and to the practical builder, 

 and I hope on behalf of the committee, to give some further facts with regard to 

 this subject at another meeting. 



I will now briefly describe the lecture room which has been constructed in ac- 

 cordance with the facts and principles stated above, so far, at least, as they could 

 be applied. 



There was another object kept in view in the construction of this room besides 

 the accurate hearing ; the distinct seeing. It was desirable that every person 

 should have an opportunity of seeing the experiments which might, be performed 

 as well as hearing distinctly the explanation of them. 



By a fortunate coincidence of principles, it happens that the arrangements for 

 ensuring unobstructed sight do not interfere with those necessary for distinct hear- 

 ing. 



The law of Congress authorizing the establishment of the Smithsonian Institu- 

 tion directed that a lecture room should be provided, and accordingly in the first 

 plan one-half of the first story of the main building was devoted to this purpose. It 

 was found, howevei*, impossible to construct a room on acoustic principles in this 

 part of the building which was necessai'ily occupied by two rows of columns. The 

 only suitable place which could be found was therefore on the second floor. The 

 main building is 200 feet long and 50 feet wide ; but by placing the lecture room 

 in the middle of the story a greater width was obtained by means of the projec- 

 ting towers. 



The main gallery is in the form of a horse shoe, and occupies 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 ceiling is twenty-five feet high, and therefore within the reach of percep- 

 tibility. It is perfectly smooth and unbroken, with the exception of an oval 

 opening near the platform, through which light is admitted. 



The seats are arranged in a curved form, and were intended to rise in accordance 

 with the panoptic curve originally proposed by Professor Bache, which enables 

 every individual to see over the head of the person immediately in front of him. 

 The original form of the room, however, did not allow of this intention being fully 

 realised, and therefore the rise is rather less than the curve would indicate. 

 The general appearance of the room is somewhat fan-shaped, and the speaker is 

 placed as it were in the mouth of an immense trumpet. The sound directly from 

 his voice, and that from reflection immediately behind him, is thrown forward upon 



