[Illustration: Fig. 47.--Truss suitable for use with flying machines, having aeroplanes about 6 feet to 8 feet wide.] The top of the aeroplane as well as the bottom should be covered with some light material, if the very best results are to be obtained. In another chapter I have shown a form of fabric-covered aeroplane, made by myself, that was not distorted in the least by the air pressure, and produced just as good effects as it would have done if it had been carefully carved out of a piece of wood. On more than one occasion Lord Kelvin came to my place; he said that my workshop was a perfect museum of invention. At the Oxford Meeting of the British Association for the Advancement of Science, Lord Salisbury in the chair, I was much gratified when Lord Kelvin said that he had examined my work, and found that it was beautifully designed and splendidly executed. He complimented me very highly indeed. While at my place, he said that the most ingenious thing that he had seen was the way I had prevented my aeroplanes from being distorted by the air. He spoke of this several times with great admiration, and, I think, if the fabric-covered aeroplane is to be used at all, that my particular system will be found altogether the best. [Illustration: Fig. 48.--The paradox aeroplane that lifts no matter in which direction it is being driven.] [Illustration: Fig. 49.--The Antoinette motor.] Regarding the motors now being employed, I think that there is still room for a great deal of improvement in the direction of greater lightness, higher efficiency and reliability. At the present time, flying machine motors have such small cylinders, the rotation is so rapid, and the cooling appliances so imperfect, that the engine soon becomes intensely heated, and then its efficiency is said to fall off about 40 or 50 per cent., some say even 60 per cent. This is probably on account of the high temperature of the cylinder, piston, and air inlet. The heat expands the air as it enters, so that the actual weight of air in the cylinder is greatly reduced, and the engine power reduced in a corresponding degree. There is no trouble about cooling the motor, and a condenser of high efficiency may be made that will cool the water perfectly, and, at the same time, lift a good deal more than its own weight. All the conditions are favourable for using a very effective atmospheric condenser (see Figs. 30 and 31).