Sir John MacNeill has estimated that 80 per cent. of the total wear of a road is due to traffic, the remaining 20 per cent. being due to atmospheric causes. Of this 80 per cent. 60 per cent. he considers is due to the action of horses’ hoofs where the traffic is fast, and 44·5 per cent. where the traffic is slow. General Morin estimates the wear of a road due to horses’ feet to be two-thirds of all causes. There can be no doubt that the action of horses’ feet, shod as they are with heavy iron shoes with long toe pieces and heels, must have a destructive effect upon the surface of a carriage-way, and this may be easily observed when watching the ruts formed by any continuous line of traffic in a roadway. The following remarks from a report of the Society of Arts on this subject may here be of interest. “It may be mentioned that as respects the horses’ shoes, attention has long been called to its defects by Sir Francis Head and others, but Sir Joseph Whitworth now points out the achievement of a decided and important improvement, which will have a large effect in road conservancy, as well as the reduction of noise. The improvement consists in the fastening of a rim of hardened steel, of about half-an-inch square, to the horses’ feet, and letting the frog grow to its natural size. One effect is to reduce by five-sixths the weight of the old shoe, or in other words to reduce by five-sixths the weight of the iron hammers constituted by the common horses’ shoes, pounding the road surface, and creating road dust and dirt, and distributing it about. The saving in this respect, as well as the reduction of noise by the reduction of the weight of rim, and also the saving of road wear, would warrant the imposition of the stimulus of a tax, or a toll upon heavy horses’ shoes to hasten this removal.”[8] Up to the present date, however (1883), no general change has been effected in the manner of shoeing horses, notwithstanding these admirable remarks of Sir Joseph Whitworth upon the subject. With reference to the question of traction upon roads General Morin, in his ‘Expériences sur le Tirage des Voitures,’ states that the resistance to the rolling of vehicles upon solid metalled roads and pavements is proportional to the weight and inversely proportional to the diameter of the wheels. On solid roads he states that the resistance is nearly independent of the width of the tires when they exceed 3 or 4 inches, but on a compressible face it decreases in proportion to the width of the tire; the resistance further increases with the velocity on hard roads, but does not do so when they are soft. The following table is almost universally now adopted as showing the traction upon level roads formed of different materials, asphalte being taken as the standard of excellence in this respect.