hooked to it, going through a small stuffing box into a boiler, where it has a atone hung on it ; this stone is balanced by a weight hung at the other end of the lever, so that when the stone is covered with water, the weight keeps the valve shut, and prevents any water getting down into the boiler ; but as the water sinks in the boiler, the weight of the stone overcomes the weight, and opens the valve ; the water in the cistern now runs down the pipe, 5, into the boiler, and raises the water and the stone until it closes the valve.
It will easily be seen, that by the con denser being constantly supplied with hot steam, which will give out its heat, and at length render the water surround ing it, in the cistern, G, so hot, that it would condense no more ; to prevent this, it is constantly supplied with cold water from a pump, T, worked by a rod from the great beam, B : the water from the cistern runs off by a waste pipe at the back of the cistern, not seen in the figures. V is a short pipe upon the boiler, with a lid and stuffing box ; a rod passes through it, and has a valve within it, pressed down by a lever and weight, v. If at any time, when the engine is
not at work, the steam should be heated, so as to be in any danger of bursting the boiler, the valve will lift up the weight, and allow the steam to escape through the pipe W, into the open air. Y, a lid screwed down upon a hole in the boiler, through which a man enters the boiler to clean it occasionally. At Z are two cocks upon the ends of pipes going down into the boiler ; one pipe is longer than the other, the longest reaches into the water, and the short one does not : these cocks are to show the height of the wa ter in the boiler ;, when one is turned (if the water is the proper height) it will deliver steam, and the other water.
It may be observed, that when the en gine is once set to work, the lever n n, on the spindle of the rack is of no use, as the instant the cock is turned one fourth round, the piston and engine be gin to return.