The first improvement on the original wooden rail pegged on to the sleepers was the fastening on it of another rail, in order that this could be removed, when worn down, without interfering with the sleepers. This arrangement was known as the "double way"; and Nicholas Wood says of it: "The double rail, by increasing the height of the surface whereon the carriage travelled, allowed the inside of the road to be filled up with ashes or stone to the under side of the upper rail, and consequently above the level of the sleepers, which thus secured them from the action of the feet of the horses." He adds that on the first introduction of the double way the under rail was of oak, and afterwards of fir, mostly six feet long, and reaching across three sleepers, and was about five inches broad on the surface by four or five inches in depth. The upper rail was of the same dimensions and almost always made of beech or plane tree. The next improvement was the nailing of thin strips, or "plates," of wrought iron on to the double rail wherever there was a steep descent or a considerable curve, thus diminishing the friction. These "plates" were about two inches wide and half an inch thick, and they were fastened on to the wooden rails with ordinary nails. They constituted the first step towards the conversion of wooden rail-ways into an iron road, and Nicholas Wood thinks it very likely that the diminution of friction resulting from their use may have suggested the substitution of iron rails for wooden ones. Cast-iron rails began to come into use about 1767. Their brittleness was, at first, found to be a great disadvantage; but this defect was subsequently overcome, to a certain extent, by the use of smaller waggons, which allowed of a better distribution of weight over the rail. Then in or about {204}1776 "plates" or "rails" (the two expressions seem to have been used somewhat indiscriminately) were cast with an inner flange, from two to three inches high, so that waggons with ordinary wheels could be taken upon them and be kept on the plate, or rail, by means of this flange. John Curr, manager of the Duke of Norfolk's collieries, near Sheffield, who claimed to have invented these flanged "plates," describes them in his "Coal Viewer and Engine Builder's Practical Companion" (1797), as being six feet long, three inches broad, half an inch thick, from 47 lbs. to 50 lbs. in weight, and provided with nail holes for fastening them direct on to oak sleepers. Lines so constructed became known as "plate-ways," "tram-ways," or, alternatively, "dram-ways."