28 On the Construction of Buildings 
windows in the walls, inducing cold counter currents, which, in 
descending, bring down with them also the noxious vapors from 
above to mingle with the air of the room again.* This is an ad- 
ditional reason why windows in this situation should be as infre- 
quent as possible ; (we have before hinted at their injurious acous- 
tic influence in other respects). 
Again the various accessories and appendages to the main apart- 
ment are often a source of offence. Corridors, lobbies and entries, 
imperfectly warmed and ventilated, will give rise to sudden gusts 
and eddies of cold air, alike uncomfortable to the audience and 
injurious, in their general effect on sound. Much can be done 
here, as suggested by Dr. Bell, by duplicating the doors at the 
extremities of every passage or entry, so that the one in front is 
not opened till that in the rear has thrown itself to.t Under- 
neath deep galleries the atmosphere is in a different state from 
that in the body of the room, and hence the difficulty often ex- 
perienced in hearing distinctly in such situations. Moreover the 
heated air which there collects, is all the while pouring out in 
front, whence it rises in a tenuous wavy i; 
sheet to the roof, to the manifest discom- 
gallery, between it and the wall, as in al 
the annexed figure, would obviate these \ 
evils and aid in preserving the unity and 
homogeneity of the air in the main body 
of the house. | ¥ 
Care also should be taken in the ar- 
rangement of the ventilators in the ceil- ci ee om 
ing, that too much sound do not escape with the vitiated air. 
_ Dr. Wyman instances the case of a chapel, in which an opening 
for ventilation was made in the ceiling of an organ loft, directly 
over the organ. He states that when the chapel was crowded, 
and the current through the opening considerable, the organ be- 
e nearly inaudible to those upon the floor; the difficulty 
ning. Sound, we have 
seen, does not easily turn at right-angles; taking advantage of 
this fact, these outlets, as we have elsewhere explained, can be 
cold glass in disturbing the quies- 
0 Wyman’s Treatise, page 125. 
ct, the cross draughts, supplies from sources and emissions of air at points 
not determined by the motive power, would be utterly inconsistent with any uni- 
formly arranged plan. As Dr. Reid well remarks, the apartment to be ventilated on 
a scientific plan, is to be deemed and treated as a piece of philosophical apparatus, 
results of the operation of — are to he interfered with by no fortuitous in- 
P 
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