The greatest improvement in implements during this period was in the direction of reaping and mowing machines, which have now attained a high degree of perfection. As early as 1780 the Society of Arts offered a gold medal for a reaping machine, but it was not till 1812 that John Common of Denwick, Northumberland, invented a machine which embodied all the essential principles of the modern reaper. Popular hostility to the machine was so great that Common made his early trials by moonlight, and he ceased from working on them.[677] His machine was improved by the Browns of Alnwick, who sold some numbers in 1822, and shortly afterwards emigrated to Canada taking with them models of Common's reapers. McCormick, the reputed inventor of the reaping machine, knew the Browns, and obtained from them a model of Common's machine which was almost certainly the father of the famous machine exhibited by him at the Great Exhibition of 1851. Various other inventors have assisted in improving this implement, and in 1873 the first wire binder was exhibited in Europe by the American, W.A. Wood, wire soon giving place to string owing to the outcry of farmers and millers. The self-binding reaper is the most ingenious of agricultural machines, and has been of enormous benefit to farmers in saving labour. Though the hay-tedding machine was invented in 1814 it is only during the last thirty years that its use has become common, the spread of the mowing machine making it a necessity, cutting the grass so fast that only a very large number of men with the old forks could keep up with it. The tedder also rendered raking by hand too slow, and the horse-rake, patented first in 1841, has immensely improved in the last thirty years. Another enormous labour saver is the hay and straw elevator, having endless chains furnished with carrying forks at intervals of a few feet, driven by horse gear. The steam cultivator invented by John Fowler is much used, but cannot be said to have superseded the ordinary working stock of the farm, though for deep ploughing on large farms of heavy land it is invaluable. Improvements in dairying appliances have also been great, but the English farmer has generally fought shy of factories or creameries, so that his butter still lacks the uniform quality of his foreign rivals. In manures the most important innovation in the last generation has been the constantly growing use of basic slag, formerly left neglected at the pit mouth and now generally recognized as a wonderful producer of clover.