with Reference to Sound. 25 
mass of heated air with which they are mingled. Hence is des 
rived an important indication for an effectual system of artificial 
ventilation. And it seems to us especially necessary in the pres- 
ent case, that, whatever modification circumstances may require 
in other respects, the plan of introducing the pure air from below 
and providing for its discharge above, when vitiated, should be 
rigidly adhered to. Thus shall we most readily and quietly en- 
sure the removal of all existing elements of acoustic disturbance, 
with the least danger of admitting new causes of a like tendency. 
In a room, containing a crowded auditory, artificially lighted 
and warmed in the usual manner, the air becomes rapidly loaded 
with the products of respiration and combustion, and, too often, 
by the addition of coal gas from the furnace flues. The changes 
induced by these processes, in the surrounding medium, are ab- 
straction of oxygen and the addition of carbonic acid gas and 
moisture, with inequality of temperature and the creation of nox- 
ious draughts at various points, all which tend to destroy that 
homogeneous and equable state of the air which we have foun 
so desirable in its acoustic relations.* With a given audience the 
result of these changes upon sound is appreciable in a degree 
usually inversely proportioned to the cubic capacity of the room. 
In its general provisions, the plan adopted by Dr. Reid for ven- 
tilating the temporary House of Commons seems admirably fitted 
0 meet the exigencies of the case. His system was devised ex- 
pressly to satisfy both the sanatory and acoustic requirements of 
that room. We take the following condensed account of it from 
the published address of Dr. Bell before quoted from. 
“* A series of openings through the wall into a court-yard, admits the 
fresh external air to the basement of the building. A suspended fib 
rous veil, 42 feet by 18, hangs before the external openings, the object 
of which is to separate the mechanical impurities, especial y the flakes 
of soot, ef which the London atmosphere is full, 200,000 visible por- 
tons having been arrested in a single evening. 
_ The air thus screened, is next passed into a receiving chamber, con- 
Stituting about one-third of the basement. A partition divides this its 
Whole length. At the middle of this wall, an opening permits the air 
to pass through an apparatus in which, by a thousand jets of water eros- 
sing each other in every direction, it is washed and moistened. It then 
* Tt has been determined f iments on animals and from its observed ef 
fects on men, that an atmosphere containing one per cent. of carbonic acid gas 
pate considered injurious to health, and as requiring immediate ven 
, p. 78. ie 
. T. Brande, Esq., states that he once examined the air in the t 
Covent Garden Theatre, and found in it three per cent. of carbonic ack 
ted by vitiati imperfect ventilation, The same gentleman also 
gas destroys (for breathing) thrice its of oxygen and fifteen times 
—Vide R. 2, ‘om A on House of Commons Bu ppe 
t For the ixed ia in obscuring and sting” 
is referred to t the first part 0 this essay. 
Stoonp Serres, Vol. XVI, No. 46,—July, 1853. 4 
