334

Newsham’s Engine.

[Book III.

not perform; neither do they throw one fourth part of their water on thefire, at the like distances, but lose it by the way; nor can they use leatherpipe with them to much advantage, whatever necessity there may be forit. The five large sizes go upon wheels, well box’d with brass, fitted tostrong iron axles, and the other is to be carried like a chair.”

No. 150 is a vertical section of the pumpsin Newsham’s engine, with the air vesselbetween them, and showing also the sectorsand chains by which motion is transmittedfrom the levers to the piston rods, and thelatter preserved in a perpendicular position.The chains are similar to watch chains intheir construction, and the length of eachis equal to the arc of one of the sectors.Four are used, two to each sector. Theirmode of Operation is in this manner : Oneend of a chain is fastened to the top of apiston rod, by a bolt and nut as represent-ed, and the other end riveted to the lowerextremity of the sector; so that when thelatter is turned down by depressing thelever, it necessarily draws, by this chain,the piston down with it. Another chain isfastened in the same manner to the lowerpart of the piston rod, (that is above the cy-No. 150. Section of Newsham’s Engine. an( J upper extremity of the

sector, and hence when the lever is elevated, this chain raises the piston withit. He probably derived the idea of thus working them from Newcomen’smode of working pumps by the atmospheric steam-engine. The roundopening below the valves in the above figure, is where the suction pipeis continued to the hose, shown at one end of the cistern in the next figure.

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No. 151. New&ham’s Fire-Eugine, A. D. 1740.