Before leaving this question of heat-engines and passing to the more important inventions by which Ericsson will be remembered, it may be as well to say a few words concerning the solar-engines to which he devoted many years' time, and one of which I saw in operation in the back yard of the pleasant old house in Beach Street, opposite the freight depot of the Hudson River Railroad. This house, by the way, which Ericsson occupied for nearly forty years, faced on St. John's Park, the pleasant square which was afterward filled up by the railroad company. Toward the last years of Ericsson's life the neighborhood became anything but a pleasant one to live in; it was dirty and noisy. Nevertheless Ericsson refused to move. Perhaps the unpleasantness of the surroundings made him the recluse he was. It is not surprising that he should have been attracted by the possibility of obtaining power from the heat of the sun. In an early pamphlet on the subject he says: "There is a rainless region extending from the northwestern coast of Africa to Mongolia, nine thousand miles in length and nearly one thousand miles wide. In the Western Hemisphere, Lower California, the table-lands of Guatemala, and the west coast of South America, for a distance of more than two thousand miles, suffer from a continuous radiant heat." Ericsson estimated that the mechanical power that would result from utilizing the solar heat on a strip of land a single mile wide and eight thousand miles long would suffice to keep twenty-two million solar-engines, of one hundred horse-power each, going nine hours a day. He believed that with the exhaustion of European coal-fields the day for the solar-engine would come, and that those countries which possessed unfailing sunshine, such as Egypt, would displace England, France, and Germany as the manufacturing powers of the world, for the European would have to move his machinery to the borders of the Nile. By concentrating the rays of the sun upon a small copper boiler filled with air Ericsson was enabled to work a little motor, and for some years he also attempted to produce steam by means of heat from the sun. He was not successful, however, in making anything of commercial value in this direction, and so far as I have been able to learn none of the tropical countries invited by him to take up the problem for its own benefit responded to the invitation.