Working Ship Pumps by Ropes.

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Chap. 7.]

one end of the shaft of the cog wheel; over this a rope is passed andcrossed below, to whieh any number of men, on each side, may applytheir strength. Both parties pull the rope towards them by turns, andthereby impart the requisite movement to the cog wheel, and consequentlyto the pump rods and suckers, as shown in No. 92. Mr. Adams, in hisLectures on Natural Philosophy , published in 1794, observed that thesekind of pumps had been “ in general use in the royal navy for five or sixyears.” Vol. iii, 392.

No. 92. Working - Ship Pumps by Ropes .

In 1813, the London Society of Arts awarded a medal and twentyguineas to Mr. P. Hedderwick, for various modes of imparting motion totwo pistons in the same cylinder, by a series of levers, instead of cog wheelsand racks. Trans, vol. xxxii, 98.

Atmospheric pumps with two pistons are used in the French marine,and are ärranged so as to be worked by the men as in the act of rowing.Neither racks nor pinions are used in communicating motion to therods. The upper ends of these are continued outside the cylinders andbent a little outwards, and then connected by a bolt to each end of a shortvibrating beam which is moved by the men. The rods do not descendin the centre of the cylinder, as in the preceding figure, but are attachedto one side of the suckers. The lower rod passes through an opening inthe upper sucker, which is closed by a collar of leather. Hachette’sTraite Elementaire des Machines. Paris 1 , 1819, p. 153.

Pumps with double pistons are not of modern date : there is one figuredin Besson’s Thöatre des Instruiüens.

The alledged superiority of these pumps is more specious than real.It is true the inertia of the water in ascending the pipes has not to beovercöme at every stroke, as in the common pump, since its motion throughthein is continuous; nör is its direction changed, as when two separatecylinders are used, being then diverted into them from the pipes at anglesmore or less acute. These are real advantages; but if we mistake not,they are the only ones, unless taking up less room on ship board be an-otherl But from the cylinders being twice the ordinary length, thesemachines are really double pumps; having not only two suckers and tworods, but also two cylinders, and requiring twice the power to work them.The principal difference between them and the üsual double pump, is thatthe cylinders are united together on the same axis, while in the latter,they are placed parallel to each other. In point of economy, we thinkpumps with two distinct Cylinders are preferable; they are less complex,and of course less liable to derangement: a longer stroke can be ob-tained in them, and, what is of more importance, when one is disordered,the other can be continued in use. On these considerations we believedouble piston pü'mps were abandoned in the British navy.

A singulär modification of the : common pump was devised in Englandm 1819, for which the Society of Arts awarded a premium of twentyguineas. The chamber was curved, and the centre of the circle, of which