Page:Inland Transit - Cundy - 1834.djvu/41

 theoretical reasoning above given would require great modification; and the resistance, which in practice is in every case greater than in the proportion of the square of the velocity, is considerably above that proportion in the case of canals. Experiments have been made by Mr. Bevan on the resistance to vessels moved at different speeds in water, and we find by them that a vessel moved on the Paddington Grand Junction Canal, at the rate of 2 miles an hour, loaded with 21 tons, required force of traction amounting to 77 lbs.; while the same vessel moved at the rate of something less than 4 miles an hour, required a force of traction amounting to 308 lbs. Thus, while the speed was increased in a somewhat less proportion than 2 to 4, the resistance was increased in the proportion of 2½ to 10. Experiments made by Mr. Walker on the London Docks give the resistance also in a greater proportion than that of the square of the velocity. Many other facts confirm this conclusion; but a singular anomaly appears to have been presented by some experiments made on the Forth and Clyde Canal in July, 1830. A twin-boat, loaded with 5 tons, 16 cwt. 41 lbs., and dragged by horses, was furnished with an instrument by which the force of traction was measured, and it was found, that at and under eight miles an hour, the resistance was in conformity with the principle just explained, but that when higher rates of speed were attained, although the resistance increased, it did not increase in nearly so rapid a proportion. This arose from the circumstance of the boat-speed having been more raised or less draft in the water by the effect of traction on the bank at the high speed. But be this as it may, the deviation from the law takes place in such extreme cases, and