The system of drainage, or sewerage, in these towns, is as bad as in most English ones. All towns situated on rivers or streams drain into them, instead of into main sewers constructed parallel to their sides. This is a most important point in the system of town arrangement; and though it has been utterly neglected in the case of London, and the waters of the Thames have become, in consequence, unfit for use, yet this ought rather to have served as a warning beacon for provincial towns, than as an object of imitation. The omission of such sewers in Scottish towns is the more remarkable, as the inhabitants are fully aware of the value of liquid manure, a great quantity of which might be thus saved from waste. If the evil be not checked speedily, it will be found a very serious nuisance at no distant period, when, in addition to contaminating the air, it has polluted the only waters accessible to the poor. To render these sewers efficient for all the purposes for which they are calculated, they should be commenced farther up the river, and be continued further down its banks, than the town reaches; and their lower extremities should deliver their contents into a pond, for evaporation, at least a mile from the town. In many situations, instead of evaporating the water in the pond, it might be employed, as it comes from the town, to irrigate adjoining grass lands, or pumped up into water-carts, to be used, in various ways, as liquid manure. In some cases, it might be worth while to erect a small steam-engine and scoop-wheel, like those in the fenny districts, for the purpose of raising the comparatively thinner waters of the sewer to an elevated channel, which channel might convey them to a distance, for the purpose of irrigation. By having two ponds for the deposit, the dense mud of the one pond would be drying, while the other pond was filling and the mud being deposited, as in the case of the ponds near Paris employed in evaporating the material which forms the poudrette. Were a sewer of the description alluded to carried down the London and Southwark sides of the Thames, at a short distance from its banks, going on a level round the docks, and under the canals, &c., the quantity of most valuable manure that might be deposited on the meadows of Essex, and the shorelands of Kent, almost exceeds calculation. The water of the Thames, being thus left pure, might be pumped up by steam-engines, for the supply of the metropolis. This is an arrangement that must sooner or later be adopted, even in London, and in all old towns; and it ought to be one of the first objects of attention, in forming new congregations of houses, in every part of the world.
