The method of measuring the final speed of the launching car for the models consisted in fastening a strip of smoked paper to the launching car in such a position that it was drawn past a stylus fastened to the end of a vibrating tuning fork placed at the end of the track. This had proved perfectly successful, but it gave a record merely of the final speed attained by the car at the moment of launching the aerodrome. In the case of the large aerodrome it was desirable to have a record of the speed of the car during the first few feet, and also at several other points in its travel down the launching track, and the more numerous these points the better. Short strips of copper were accordingly placed every twelve inches along the length of the track, and these were connected by a wire to one terminal of a small electric battery. Mounted on the car, in such a way that it would be drawn across these contact strips, was a copper brush arranged to make continuous contact with another wire stretched along the track, this second wire being connected to the other terminal of the electric battery and having in its circuit the magnet which actuated a pen on a chronograph. Since the rate of revolution of the chronograph barrel was known, the [p163] distance between the marks which the magnet would cause the pen to make when its circuit was closed by the brush on the car passing across the contact strips on the track would give correct measures of the time consumed by the car in passing over each twelve inches of its travel. Upon test, however, it was found impossible to get the chronograph magnets to work rapidly enough to respond to the very rapid opening and closing of the circuit after the car had passed over the first one-quarter of its length of travel. As a large part of the slowness of action seemed to be due to the weight of the fountain pens, they were replaced by small glass tubes drawn out to a fine point and containing a small amount of ink. These seemed, however, to be still too heavy to respond to the rapid closing of the circuit unless the contacts were made unduly long. The contacts were finally made three inches long and placed only every three feet along the track, but just as these contacts were completed and placed in position the clock-work of the chronograph itself became deranged. Before it could be repaired, the tests were discontinued, as everything was in readiness for the boat to proceed down the river where the actual tests in free flight were to be made. Tests of the final speed of the car were, however, made by the tuning-fork method, and the springs were adjusted until their tension was sufficient to cause the car to attain a speed of thirty-five feet a second at a point three inches in front of the point at which the aerodrome would be released from the car. [p164] CHAPTER V CONSTRUCTION OF FRAME OF LARGE AERODROME