211 



has been retained in all later air-pumps. In using the pump, the 

 piston, with the aperture in it open, was forced to the bottom of the 

 cylinder. The stick was then thrust into the hole in the piston, 

 and the latter drawn up. It ascended lifting the water with it, and 

 leaving a vacuum below. When the piston had risen above the 

 mouth of the tube communicating with the receiver, the stop-cock was 

 opened, and the air of the receiver allowed to expand into the cylin- 

 der. The stop-cock was then shut, the stick pulled out of the aper- 

 ture in the piston, and the latter forced to the bottom of the cylinder. 

 The air bubbled up through the aperture, and when it had escaped, 

 the stick was inserted into the hole in the piston, and the manipu- 

 lations proceeded as before. If the stop-cock were opened, as it was 

 liable to be, at the wrong stroke, the receiver, instead of being 

 emptied of air, was filled with water. 



Six or seven years again elapsed, without any further improvement 

 being effected on the English air-pump. In 1676, the celebrated 

 and ingenious Frenchman, Denis Papin, came to England, bringing 

 with him a novel pneumatic engine, and became Boyle's assistant. 

 An engraving and description of Papin's air-pump are given in 

 Boyle's tract entitled " A Continuation of New Experiments, &c., 

 touching the Spring and Weight of the Air, and their effects. Second 

 Part." — {Birch's Boyle, 2d Ed., vol. iv., p. 505.) The great pecu- 

 liarity of Papin's air-pump, as contrasted with former air-pumps, was, 

 that it had two barrels, but it had other distinctive arrangements, 

 which makes it singular that it should have been overlooked by later 

 writers on Pneumatics. 



It had two pumps standing side by side, the mouths of the barrels 

 being turned upwards. Each of the piston-rods terminated in a stir- 

 rup attached to its upper end, and the stirrups were connected by a 

 rope or cord, which passed over a vertical grooved wheel or large 

 pulley. To work the machine, the exerciser of the pumps, as he is 

 called in the original account, put his feet into the stirrups, and hold- 

 ing on, as it should seem, by his hands to the upper part of the frame- 

 work of the air-pump, or leaning against it (for the description is not 

 precise on this particular), moved his feet alternately up and down as 

 a handloom weaver does, or a culprit on the treadmill. The pistons 

 or suckers had valves (probably of bladder) opening upwards like that 

 of an ordinary water-pump, and similar valves weie placed at the 

 bottom of the cylinders, which were filled with water to a certain 



