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into the lungs, and which, no doubt, cause irritation there; the 
other is by lessening the amount of daylight. It not only diminishes 
the allotted proportion of sunshine, but it interferes with the quality 
to no less degree than with the quantity of the light we receive. 
Objects seen through an atmosphere thus polluted, appear of an 
unnatural yellowish colour, because the light by passing through 
the yellow smoke, is deprived to some extent of the blue and 
violet rays which constitute the most refrangible portion of the 
spectrum ; while the yellow, orange, and red rays, being less re- 
frangible, are able to pass through ; and it happens also that those 
rays which are cast off are those which are of most value in the 
promotion of healthy living action. Light certainly is not life, 
but it is-very essential to it; and I remember seeing somewhere 
an account of some very interesting observations, showing the 
relative amount of cures in the two sides of a hospital—one 
receiving the sunshine, the other shaded. There was a very 
marked difference, and the light side was by far the most successful. 
Passing from the black smoke to the contamination of the air 
by invisible gases resulting from the burning of coal, we come to 
perhaps the most serious matter in connection with air pollution 
in towns from artificial causes, since chemical works are now 
under inspection, and do not therefore allow so much refuse to 
escape into the air as previously, and also because this pollution is 
very general, each chimney contributing its share. 
Most coals contain sulphur, and they consequently produce 
sulphur acids when burnt. If we take the average amount of 
sulphur in coal at one per cent.—although this is in reality not so 
high as the true average—we should produce, by burning a ton of 
such coal, about forty-four pounds of sulphurous acid; and this 
forty-four pounds of sulphurous acid, by passing into the air and 
coming in contact with the aqueous vapour contained in the 
atmosphere, would be gradually changed to about fifty-five pounds 
of dry sulphuric acid, or seventy pounds of strong oil of vitriol. 
This we observe is from one ton of coal; and if we consider that 
many establishments consume even as much as twenty tons daily— 
and there are dozens of these establishments in many towns—we 
hy 
