All About Engines

24 All About Engines other great inventions, it was preceded by a long chain of fruitless endeavour. From the first dis- covery of fire and the effect of heat upon water, the latent power in the steam which escaped in bubbles from its surface must have been dimly recognised. That this invisible giant revealed its strength in many ways—sometimes to the hurt of the curious—can hardly be doubted. In all probability some of its secrets were discovered, but were lost again by the simultaneous death of those who had dared to pierce the veil. The mists of antiquity hide many a triumph, and not a few grim tragedies. Two thousand years ago, in the great city of Alexandria, at the mouth of the Nile, lived one Hero, who seems to have made many ingenious experi- ments with fire and liquids and gases. And among other things he invented a steam engine. From an inspection of Fig. 12, Plate 1, it will be seen that it con- sisted of a boiler with two upright tubes, bent at right angles at the upper ends. A ball of metal, with short, straight tubes fixed on opposite sides, was placed between the upright tubes, so that it could spin round on a horizontal axis. Two other tubes, bent at right angles, were fixed to the ball in the position shown in the figure. When a fire was lighted be- neath the boiler the water boiled, steam entered the ball and escaped from the bent tubes, and owing to changing its direction in the bent tubes it urged the ball round. Models of Hero’s engine, made in glass, can be purchased from any scientific instrument makers for a small sum. But a more satisfactory