1856] 



WRITINGS OF JOSEPH HENRY. 419 



Fahrenheit's scale, if we know the temperature of the room 

 and that of the heated current the amount of angular refrac- 

 tion can be ascertained. But since the ear does not readilj^ 

 judge of the difference of direction 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 conclude that the in- 

 distinctness produced by refraction is comparatively little. 

 Professor Bache and myself could perceive no difference in 

 distinctness in hearing, from rays of sound passing over a 

 chandelier of the largest size in which a large number of 

 o-as jets were in full combustion. The fact of disturbance 

 from this cause however, (if any exist,) may best be deter- 

 mined by the experiment with a parabolic mirror and the 

 hearing-trumpet before described. 



These researches might 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. 



The Smithsonian Lecture-room. — I shall now briefly describe 

 the lecture-room of the Smithsonian Institution, which has 

 been constructed in accordance with the facts and principles 

 previously stated, so far at least as they could be applied. 



There was another object kept in view in the construc- 

 tion of this room besides the accurate hearing, namely the 

 distinct seeing. It was desirable that every person should 

 have an opportunity of seeing the experiments which might 

 be performed, as well as of distinctly hearing the explanation 



of them. 



By a fortunate co-incidence of principles, it happens that 

 the arrangements for insuring unobstructed sight do not 

 interfere with those necessary for distinct hearing. 



The law of Congress authorizing the establishment of the 

 Smithsonian Institution 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 pur- 



