The struts referred to above were three in number, two being placed near the rear and one at the center of the front of the car. The use of three points of support had the advantage of furnishing a rather rigid foundation against which the frame could be tightly drawn by means of the clutch-hook without risk of straining it. In designing the “underneath” launching apparatus, which was very thoroughly tested in the experiments with the models in the summer of 1899, the plan of having three struts with the aerodrome drawn tightly against them by means of a central clutch-hook was continued with most satisfactory results. When the position of the struts on this launching apparatus had been changed so as to permit it to be used for the quarter-size model, it was found, in making shop tests of the engine with the aerodrome mounted on the launching car, that, owing to the greater vibration produced by the gasoline engine, the three points of suspension did not hold the model in a sufficiently rigid manner. It became necessary, therefore, to use four struts, the two rear ones being left as before, and the single one in front being replaced by two interconnected ones arranged similarly to those in the rear. After making this change no difficulty was found in holding the aerodrome rigidly against the struts, and this modification was therefore immediately introduced in the designs for the large launching car which was already under construction. [Illustration: PL. 39 METHOD OF ATTACHING GUY-WIRES TO GUY-POSTS TO RELIEVE TORSIONAL STRAIN]