II. AIR PUMPS, ETC. 133 



shut, while the stopcock L of the receiver was open, during the descent of 

 the piston. When the piston was driven home, L was shut and G kept 

 open. In this air-pump a vacuum was produced slowly, and was impuftct 

 at best. 



587. Air Pump, with double barrel (1662), by Boyle. 



Royal Society. 



624. Diagram of the Second English Air Pump, con- 

 structed by Boyle and Hooke in 1667. 



A. Galletly, Edinburgh. 



The piston was worked by a rack and pinion like the first English air-pump, 

 but in this one the barrel was kept under water to keep the leather of the 

 piston always wet. 



The piston had an aperture at F and a stop-cock at I, which were worked 

 as in the first English air-pump. 



625. Diagram of Papin's Air Pump. 1676. 



A. Galletly, Edinburgh. 



The diagram represents only the working parts of the instrument, without 

 the frame supporting them. This air-pump had the great advantage over 

 earlier forms of having two barrels, in which case, as the air becomes 

 exhausted, the resistance which it offers to the ascent of one piston is nearly 

 balanced by the force with which it compels the other to descend. This air- 

 pump was worked by moving the feet alternately up and down in stirrups. 



618. The Abbe Nollet's Air Pump. 



Conservatoire des Arts et Metiers, Paris. 



626. Diagram of Hauksbee's Air Pump. 1703-9. 



A. Galletly, Edinburgh. 



This instrument, like Papin's, had two barrels, but the stirrup arrangement 

 and pulley are replaced by racks on the piston rods, and a pinion moved by a 

 handle, as in the modern double-barrelled air-pump. 



612. Apparatus for Air Pump. An air-gun supported 

 by two vertical mahogany pillars and cross-bar, by means of which 

 it may be adjusted to any angle. 



Museum of King George III.) King's College. 



613. Apparatus for Air Pump. Metal condenser with 

 glass ends, large enough to take a pair of four-inch Magdeburg 

 hemispheres with fittings, and a metal lever to which weights may 

 be attached to measure the pressure of the air, either when com- 

 pressed or at its ordinary pressure. 



Museum of King George III.) King^s College. 



614. Air Pump with two Barrels. The first pump of the 

 kind ever constructed. It is an exhausting and a condensing 

 pump, and was made for King George III. in 1761. 



Museum of King George III., King's College. 



592. Drawing of Mercurial Air Pump (1872). 



J. P. Joule, D.C.L., F.R.S., Manchester. 



