Cyrus McCormick's plough was a success that encouraged him to take hold of the more difficult problem of the reaper. He found that some device, such as his father's, would cut grain after a fashion, provided it was in perfect condition and stood up straight; the moment it became matted and tangled and beaten down by wind and rain the machine was useless. Other devices had been arranged whereby a fly-wheel armed with sickles slashed off the heads of the wheat, leaving the stalks; but here again such a machine would work only when the field was in prime condition. He determined that no device was of any value which would not cut grain as it might happen to stand, stalk and all. After months of labor in his father's shop, making every part of the machine himself, in both wood and iron, as he said, he turned out, in 1831, the first reaper that really cut an average field of wheat satisfactorily. Its three great essential features were those of the reaper of to-day--a vibrating cutting-blade, a reel to bring the grain within reach of the blade, a platform to receive the falling grain, and a divider to separate the grain to be cut from that to be left standing. This machine, drawn by horses, was tested in a field of six acres of oats, belonging to John Steele, within a mile of Walnut Grove. Its work astonished the neighboring farmers who gathered to witness the test. The problem of cutting standing grain by machinery had been solved. There were, however, certain defects in the reaper which caused Cyrus McCormick not to put the machine on the market. All the cog-wheels were of wood. There was no place upon it for either the driver or the raker. The former rode on the near horse and the latter followed on foot, raking the grain from it as best he could. But it cut grain fast, and both father and son were so impressed by its possibilities as foreshadowed in even this crude affair, that for the next few years they devoted their time, money, and thoughts to it. Robert McCormick was as enthusiastic as his son, and he is rightly entitled to a share of the honor, for his invention of 1816 turned the attention of his son to the problem and pointed out the radical errors to be avoided. A year after its first trial, with certain improvements, the reaper cut fifty acres of wheat in so perfect and rapid a manner as to insure its practical value beyond all doubt. The self-restraint shown by McCormick in refusing to sell machines until he was satisfied with them shows the man. The patent was granted in 1834, but for six years he kept at work experimenting, changing, improving, during the short periods of each harvest. In a letter to the Commissioner of Patents, on file in the Patent Office, Mr. McCormick said: "From the experiment of 1831 until the harvest of 1840 I did not sell a reaper, although during that time I had many exhibitions of it, for experience proved to me that it was best for the public as well as for myself that no sales were made, as defects