Mr. Cochrane is far less hazardous than the Board of Health, and appears to me to arrive at his result in a more scientific and conclusive manner. He goes first to the Stamp Office to ascertain the number of horses in the metropolis, and then requests the professors of the Veterinary College to estimate the average quantity of excretions produced by a horse in the course of 24 hours. All this accords with the soundest principles of inquiry, and stands out in startling contrast with the unphilosophical plan pursued by the Board of Health, who obtain the result of the most crowded thoroughfare, and then halving this, frame an exaggerated estimate for the whole of the metropolis.
But Mr. Cochrane himself appears to me to exceed that just caution which is so necessary in all statistical calculations. Having ascertained that a horse voids 49 lbs. of dung in the course of 24 hours, he makes the whole of the 24,214 horses in the metropolis drop 30 lbs. daily in the streets, so that, according to his estimate, not only must every horse in London be out every day, but he must be at work in the public thoroughfares for very nearly 15 hours out of the 24!
The following is the estimate made by Mr. Cochrane:—
Daily weight of manure deposited in the streets by 24,214 horses × 30 lbs. = 726,420 lbs., or 324 tons, 5 cwt., 100 lbs.
Weekly weight, 2270 tons, 1 cwt., 28 lbs.
Annual weight, 118,043 tons, 5 cwt.
Tons or cart-loads deposited annually, valued at 6s. × 118,043 = 35,412l. 19s. 6d.
It has, then, been here shown that, assuming the number of horses worked daily in the streets of London to be 20,000, and each to be out six hours per diem, which, it appears to me, is all that can be fairly reckoned, the quantity of horse-dung dropped weekly is about 700 tons, so that, including the horses of the cavalry regiments in London, which of course are not comprised in the Stamp-Office returns, as well as the animals taken to Smithfield, we may, perhaps, assert that the annual ordure let fall in the London streets amounts, at the outside, to somewhere about 1000 tons weekly, or 52,000 tons per annum.
The next question becomes—what is done with this vast amount of filth?
The Board of Health is a much better guide upon this point than upon the matter of quantity: “Much of the horse-dung dropped in the London streets, under ordinary circumstances,” we are told, “dries and is pulverized, and with the common soil is carried into houses as dust, and dirties clothes and furniture. The odour arising from the surface evaporation of the streets when they are wet is chiefly from horse-dung. Susceptible persons often feel this evaporation, after partial wetting, to be highly oppressive. The surface-water discharged into sewers from the streets and roofs of houses is found to contain as much filth as the soil-water from the house-drains.”