TRANSACTIONS OF THE SECTIONS. 97 
Buildings were now erected on this principle, and contained from fifteen hundred to 
three thousand people, whom they accommodated without difficulty, and with per- 
fect comfort both to speaker and hearer. He had little doubt, from experiments he 
had recently made, that so many as ten thousand people might be so arranged as to 
hear with ease and comfort a good speaker. Mr. Scott Russell’s principle of con- 
struction is to place the speaker in the focus of a curve, which he calls the curve of 
equal hearing, or the isacoustic curve; and to place the seats of the auditors in such 
a fender that their heads shall all be arranged in this curve. 
or -— 

Let A BC D represent the vertical section of a building for public speaking, S the 
height of the speaker on his platform, D C the floor of the building : then, for the pur- 
_ pose that all the auditors should hear and see equally well, they should be placed on 
_ the line S R B of the acoustic curve. This curve is constructed in the following 
_ manner: D Cis first divided into equal parts, to represent the usual breadth of a 
_ sitting, and vertical lines are drawn through these points. R being the place of the 
_ auditor 1 ; the place of auditor 2 behind him is assigned thus—join S R, and produce 
f it to a—from a upwards set off a 2 = 9 inches, and 2 is the proper height of the 
_ mext spectator. Then join S 2, produce it to 4, and set off 6 3 = 9 inches, and 3 is 
the place of the third spectator; and so on for the place of every spectator. Such 
was the vertical section of the building. The horizontal section was either circular 
or polygonal, having the speaker at the centre. This form had been found perfectly 
successful in affording the highest degree of comfort both to hearer and speaker ; 
therefore he submitted it with confidence to the Section, as a practical and esta= 
blished principle, more than as a mere theoretical speculation. 
He next entered into an analysis of the nature and causes of the evils which are 
experienced in public buildings of a large size and of the usual forms—in so far as 
these may be deduced from the received laws of sound. These he classed as fol- 
‘lows. First, evils arising from reflexion of sounds. Second, evils arising from 
spontaneous oscillation, and the independent key-note of the building. In con- 
sidering this branch of the subject, an explanation was attempted of the fact, that 
buildings have a key-note and pitch ; and a rule for finding that pitch, practically and 
theoretically, was adduced. Third, evils arising from interferences of sound, owing 
to the disproportions and forms of buildings. These evils were all to be remedied 
by the adoption of the form given in the paper; and, on that construction, he had 
satisfied himself, that five, ten, or even twelve thousand people might be so arranged 
as to hear a single voice easily and comfortably. The second part of the paper 
examined certain phenomena in sound, with which we had not formerly been 
acquainted. Our knowledge of the laws of sound rested hitherto on an hypothesis, 
that the phenomena of sound in the air were analogous to the phenomena of water, 
when disturbed by dropping a stone on the surface of a smooth lake. In this case it 
__ is well known that the water propagates waves round the point of disturbance in all 
; directions, and that these diffuse themselves in concentric rings over the whole sur- 
saat ns TNC AEE nL RMP it OO 

_ face. In like manner it was taken for granted, that the sound-waves, produced by a 
_ sonorous body, are ofasimilar nature, and the laws of sound had been deduced from 
_ this hypothesis. These laws were, however, imperfect and erroneous. Scund did 
not resemble these waves ; therefore analogies deduced from such waves were erro- 
_ neous. These waves of water are denominated by Mr. Russell, waves of the second 
1843. H 
