224 On the Construction of Buildings 
been known that clocks and watches in such a situation will mod- 
ify each other’s motions, and compel a perfect coincidence of ac- 
tion. So two chords or organ pipes, placed in each other's vicin- 
ity, and sounded together, will often be found in unison, thoug 
their respective notes differ a little when sounded separately. In 
this way, in a powerful orchestra, one or more refractory instru- 
ments are oftentimes compelled to play in tune. On much the 
same principle we would explain the requirement of harmonic 
relations in the proportions of a building constructed for musical 
rposes. 
The subject of Catacoustics, or the doctrine of reflected sound, 
is, perhaps, the most unsatisfactory in its results of any branch of 
physical science ; and, yet, upon its due appreciation depends, in 
very great measure, our hope of success in the attempt to make 
the laws of sound of any practical value in their application to the 
question under consideration. 
This part of acoustics may be subdivided into reflection proper 
(which includes echo) and reverberation. Much indistinctness 
appears to have prevailed in the treatment of this subject by au 
thors, as well as a singular want of discrimination as to the pre 
cise cause and effect, in the case of many phenomena which are 
commonly referred to the principle of reflection of sound, and 
many ingenious theories have been offered to explain the same 
result. Keeping in mind, however, the strict analogy hereto: 
observed in the laws of light and sound, it does not seem to us 
necessary to depart here from the idea of this intimate connection. 
If an obstacle, as a blank wall, be interposed between the source 
of sound and the ear, the sonorous wave is thereby arrested ints 
direct course, and the indirect pulses only take effect. Could any 
contrivance be adopted which would mark the track of sound, the 
space behind such obstacle interposed would be left in shadow; 
and if water be the medium through which the sound is passe® 
the occlusion is still more complete, and would, in this ase; be 
equivalent to a total eclipse, as we are taught by experiments ace 
tually made. But if the point of the original sound and the heater 
be on the same side of the wall, and the ear in a favorable a 
tion, both the direct sound and the reflection from the surface 
the wall will be heard, producing a reinforcement and slight pro- 
longing of the original note or its distinct repetition, according as 
ean never otherwise than mar the genuine musical effect, 8” 
the hearer is in such close proximity to the 
