would also remain nearly constant, because as the machine advances and the screws commence to run slightly faster, an additional quantity of steam will be called for and this could be supplied by turning on more gas. When everything was ready, with careful observers stationed on each side of the track, the order was given to let go. The enormous screw thrust started the machine so quickly that it nearly threw the engineers off their feet, and the machine bounded over the track at a great rate. Upon noticing a slight diminution in the steam pressure, I turned on more gas, when almost instantly the steam commenced to blow a steady blast from the small safety valve, showing that the pressure was at least 320 lbs. in the pipes supplying the engines with steam. Before starting on this run, the wheels that were to engage the upper track were painted, and it was the duty of one of my assistants to observe these wheels during the run, while another assistant watched the pressure gauges and dynagraphs (Fig. 79). The first part of the track was up a slight incline, but the machine was lifted clear of the lower rails and all of the top wheels were fully engaged on the upper track when about 600 feet had been covered. The speed rapidly increased, and when 900 feet had been covered, one of the rear axle-trees, which were of 2-inch steel tubing, doubled up (Fig. 80), and set the rear end of the machine completely free. The pencils ran completely across the cylinders of the dynagraphs and caught on the underneath end. The rear end of the machine being set free, raised considerably above the track and swayed. At about 1,000 feet, the left forward wheel also got clear of the upper track and shortly afterwards, the right forward wheel tore up about 100 feet of the upper track. Steam was at once shut off and the machine sank directly to the earth imbedding the wheels in the soft turf (Figs. 81 and 82) without leaving any other marks, showing most conclusively that the machine was completely suspended in the air before it settled to the earth. In this accident, one of the pine timbers forming the upper track went completely through the lower framework of the machine and broke a number of the tubes, but no damage was done to the machinery except a slight injury to one of the screws (Fig. 83). [9] The quantity of water entering the boiler at this time was so great as to be beyond the range of the feed-water indicator. [Illustration: Fig. 80.--The outrigger wheel that gave out and caused an accident with the machine.] [Illustration: Fig. 81.--Shows the broken planks and the wreck that they caused. It will be observed that the wheels sank directly into the ground without leaving any track.]