LECTURES. 



EIGHTH LECTURE. 



183 



The clglitli and concluding lecture of this course embraced an out- 

 line of a series of experiments on acoustics, and a description of the 

 construction for acoustic purposes of different public buildings which 

 had been designed by the lecturer or altered under his direction. 

 After a short exposition of the leading principles of acoustics, it was 

 contended, tliough there might be no end to the peculiarity of devel- 

 opments arising from the use of new materials, new designs, and new 

 decorations, that these principles were sufficiently well known tp guide 

 construction, particularly if accompanied with adequate provisions for 

 the escape of sound, after it had effected the object desired— a point 

 that had not, so far as he was aware, met with adequate attention till 

 some of the experiments had been made which he had described. 

 Without this escape, or an equivalent absorption of sound, which was 

 not compatible with many structures and decorations, sound continued 

 too often to reverberate and interrupt the distinctness of succeeding 

 sounds. He then described rooms in various parts of Europe, where 

 the sound was audible from five to twelve seconds after the cause pro- 

 ducing it had ceased to act ; and added that in such places, supposing 

 only three syllables to be pronounced in a second, from fifteen to 

 thirty-six successive syllables were constantly ringing in the ear and 

 modifying or destroying the enunciation of every succeeding word. 



In general, sound was most beautifully distinct and clear ma wood 

 or on the surface of the ocean, no returning echo or reverberations in- 

 terfering with the sweetness or purity of each succeeding note. If a 

 room were built of properly absorbing materials, or lined with those 

 that did not reflect sound, any form could be given to it that the archi- 

 tect required. It would not be powerful in sustaining sound, but, 

 with adequate power, there would be no jarring reflections. If par- 

 allel reflecting surfaces were largely introduced and great altitude 

 given, dissonant sounds would equally destroy or mar both speech 

 and music. Good effects were attained when the highest power of 

 reflection was given near the ear of the hearer and the voice of the 

 speaker, the sound that had done its duty being then absorbed or dis- 

 charged. The object was attained in a still higher degree when the 

 reflection permitted was induced by materials that had the power of 

 vibrating independently of the general structure. Dr. Eeid then de- 

 scribed the peculiarities of the acoustics in his class-room, and the 

 trials made in it by members of government and of Parliament ; pass- 

 ing then to the old House of Commons, which he had treated as an 

 acoustic instrument, using glass and pine wood largely in the interior, 

 and combining universal ventilation with the means of escape, both 

 above and below, for the sound that had done its duty. The tem- 

 porary House of Peers he had treated in a, somewhat similar manner^ 

 but there essentially he had introduced largely a resilient surface of 

 sheet iron on both sides of the house, immediately opposite the most 

 important benches, where the tone of speaking and hearing required 

 the .highest attention. In the new House of Commons a different 

 series of arrangements had been introduced in opposition to his views^ 



