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and twenty-four times the amount at the Philosophical Hall. The amount of deposit varied at different times of the year, but the above ratio remained practically constant. The following photograph shows the appearance of two plates after a year’s exposure, one in the country and the other in town, and the difference is striking, the town plate being almost opaque, whereas the country plate appears nearly as clean as when first put out.
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| Country Plate. | Town Plate. |
This black adhesive film represents a daily deposit weighing about 25 lbs., which covers the smoke-infected area with a permanent cloak of fast colour, which will stand washing. It is this adhesive deposit which discolours buildings and blackens vegetation. Unfortunately, it does more than blacken vegetation, it fills up the pores of the leaf and gradually destroys the plant. The photograph represents a holly leaf taken from the College grounds, from one-half of which the soot has been carefully removed, and the green colour has then been bleached, the soot remaining intact. Until we can abolish smoke there seems little prospect of inducing any but the hardiest plants to flourish near the centre of our big towns.
The very birds of the air are tarred with this universal tar brush. I am indebted to Professor Ransome for a Leeds
