_s” 
VENTILATION OF SEWERS AND DRAINS. 165 
power of our local subsoils, for it is very clear that as the heating 
or cooling of air is entirely a matter of the extent of surface in 
contact with it, the heat emitting or heat absorbing power of a 
unit surface of underground channel must depend entirely on the 
rapidity with which the heat can be transferred to or from the 
general mass of the surrounding material. 
By observation of the sewer wall temperatures in the different 
strata relatively to the temperature and velocity of the air current 
passing through, and the depth below the surface, much light 
might be thrown on this subject, and Mr. Smail would confer 
further benefit on sanitary science if he would include this in the 
very valuable series of experimental investigations now in progress 
under his direction. 
I fear I have occupied rather too much time on this point, but 
would like to refer to one other before concluding, namely as to 
the action of the various ventilators in their influence on danger- 
ous or offensive matters arising with sewer air. In an article 
entitled London Fogs, in the Spectator of January 9th of this 
year, a matter is suggested which has aroused much speculation 
and discussion, namely whether the opening up of sewers to 
ventilating air currents has not really rendered the atmosphere of 
large cities (especially cities subject to fogs) more dangerous and 
unhealthy. This certainly interests us here, but, fortunately we 
are as yet under very different conditions as to fogs from London, 
Glasgow, or Manchester. These cities are in the first place more 
unfavourably located than we are, and there the smoke nuisance 
has assumed practically unmanageable proportions, partly owing 
to the vast extent of ground closely covered with buildings, and 
in many cases because of sheer carelessness or parsimony on the 
part of manufacturers. I speak of the matter advisedly because 
I acted for some time as consulting engineer to the Glasgow City 
authorities in smoke nuisance cases, and I do not hesitate to say 
that in 90% of the cases submitted to me, the nuisance was caused 
either by simple carelessness in firing or by forcing boilers or 
chimneys to do work far beyond their power. 
