448

Papin’s Air Machines.

[Book IV,

and four receivers will be sufficient for the purpose of Illustration. Thepump cylinders were open at the top. They had no valves, and but onesmall opening at the bottom of each where the long air-pipe was United;and the eapacity of each cylinder was equal to that of two receivers. Thecranks were so arranged that as one piston ascended the other descended.It was not two adjoining receivers that were connected to the same pump,but the lowest and the next but one above it, i. e. Nos. 1 and 3, while toNos. 2 and 4 the pipe of the other pump was attached. Theo as thepiston of the first mentioned pump was raised, the air in Nos. 1 and 3would be rarefied by rushing into the pump cylinder, and water would beforced into them by the atmosphere : in the mean time the other pistonwould produce a partial vacuum in Nos. 2 and 4, and they would becomefilled with the liquid contents of Nos. 1 and 3, in consequence of the airpreviously in these being driven back by the descent of the piston ; sothat as the wheel revolved, water would constantly be entering one halfof the receivers, and the contents of the other half be discharging. Howthe water was to be delivered from the highest receiver Papin has notinformed us—probably through an orifice covered by a valve openingoutwards.

This project was ingenious, but of no practical value ; and it failed evenin an experiment. In consequence of the extreme elasticity of air, andthe great facility with which it dilates and is compressed, little or no effectwas produced by the action of the pumps. When a piston descended, theair in the long pipe readily yielded to its impulse without imparting anyvery sensible compression in the receivers; and on the piston’s ascent, theair in the pipe again dilated and no sufficient rarefaction took place, inconsequence of the great distance of the receiver from the exhaustingapparatus.

On the failure of this he devised another plan. Suppose, for example,that it was required to raise water out of amine, and that there was noriver to turn a wheel to work the pumps nearer than a mile. Papin pro-posed to place two air-pump cylinders fitted with pistons near the water-wheel, and other two at the mouth of the mine. These were to be con-nected by a pipe. The action of the pistons moved by the wheel was tocompress the air in the cylinders, and in the pipe tbroughout its wholelength, under the idea that when the pistons at one end of the pipe weredepressed, those at the other would, by the communication of pressure,be elevated; but although the pistons moved by the water-wheel Con-densed the air, those at the mine stood still. The same cause that ledPapin to abandon the first device, also rendered this one useless. If airwere incompressible, the plan would have answered : had he employedwater instead of air, the machine would have performed. Nothing dauntedhowever, he tried again in 1686, and with a somewhat similar apparatus,but one whose action depended upon the rarefaction of air. Two largeair cylinders, open at top, were placed a short distance apart at the mouthof the mine, and directly over them a cylindrical shaft or axle, supportedon Journals at each end. Instead of rods being attached to the pistons, astrong rope was fastened to the centre of each, and coiled three or fourtimes round the axle in opposite directions, and fastened to it. Betweenthe cylinders a large drum or wheel was fixed upon the axle, having along rope wound round it, and the two ends (of the rope) suspended fromopposite sides reached half way down the mine. To these ends two largebuckets were attached, in which to raise the water. As the drum turnedfirst one way and then the other, one bücket would be raised and the otherlowered, like two buckets suspended over a pulley in a well. The design