In a discussion before the Society of Arts, in 1855, in which many gentlemen, experienced in drainage, took a part, this subject of obstruction by mill-dams came up. Mr. G. Donaldson said he had been much engaged in works of land-drainage, and that, in many instances, great difficulties were experienced in obtaining outfalls, owing to the water rights, on the course of rivers for mill-power, &c. Mr. R. Grantham spoke of the necessity of further legislation, "so as to give power to lower bridges and culverts, under public roads, and straighten and deepen rivers and streams." But, he said, authority was wanting, above all, "for the removal of mills, dams, and other obstructions in rivers, which, in many cases, did incalculable injury, many times exceeding the value of the mills, by keeping up the level of rivers, and rendering it totally impossible to drain the adjoining lands." Mr. R. F. Davis said, "If they were to go into the midland districts, they would see great injury done, from damming the water for mills." In Scotland, the same difficulty has arisen. "In many parts of this country," says a Scottish writer, "small lochs (lakes) and dams are kept up, for the sake of mills, under old tenures, which, if drained, the land gained by that operation, would, in many instances, be worth ten times the rent of such mills." In the case of the Rye and Derwent Drainage, an account of which is found in the 14th Vol. of the Journal of the Royal Agricultural Society, a plan of compensation was adopted, where it became necessary to remove dams and other obstructions, which is worthy of attention. The Commissioners under the Act of 1846, removed the mill-wheels, and substituted steam-engines corresponding to the power actually used by the mills, compensating, also, the proprietors for inconvenience, and the future additional expensiveness of the new power. "The claims of a short canal navigation, two fisheries, and tenants' damages through derangement of business during the alterations, were disposed of without much outlay; and the pecuniary advantages of the work are apparent from the fact, that a single flood, such as frequently overflowed the land, has been known to do more damage, if fairly valued in money, than the whole sum expended under the act." Under this act, it became necessary for the Commissioners to estimate the comparative cost of steam and water-power, in order to carry out their idea of giving to the mill-owners a steam-power equivalent to their water-power.