II. AIK PUMPS, ETC. 159 



608. Two smaller Magdeburg Hemispheres of brass. 



Professor Dr. H. Weber, Brunswick. 



The two smaller hemispheres of brass were used for experiments with 

 weights (page 106, Tab. XII., of Otto von Guericke's " experimentanova"). 



598. Two Magdeburg Hemispheres. 



Professor Dr. Lepsius, Berlin. 



599. " Ottonis de Guericke Experimenta nova (ut 



vocantur Magdeburgica) de Vacuo spatio." Primum a R. P. 

 Gaspare Schotto e Societate Jesu et Herbipolitanae Academiae 

 Matheseos Professore : nunc vero ab ipso Auctore perfectius 

 edita, variisque aliis Experimentis aucta. Quibus accesserunt 

 simul certa quaedam de Aeris Pondere circa Terram, de Virtutibus 

 mundanis, et Systemate mundi planetario, sicut et de Stellis fixis, 

 ac Spatio illo immenso quod tarn intra quam extra eas funditur. 



Amstelodami apud Joannem Janssonium a Waesberge, Anno 

 1672. Cum Privilegio S. Caes. Majestatis. 



Professor Dr. Lepsius, Berlin. 



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



Royal Society. 



622. Diagram of Von Guericke's Air Pump. Invented 

 1654. A. Galletly, Edinburgh. 



It consisted of a globe of copper, with a stopcock, to which a pump was 

 fitted. 



The pump-barrel was entirely immersed in water to render it air-tight. 

 This was the earliest of all air-pumps. 



623. Diagram of the First English Air Pump, constructed 

 in 1658-59 by Hooke and Boyle, but mainly by the former. 



A. Galletly, Edinburgh. 



As shown in the diagram, it had a single barrel, in which was a piston 

 worked by a rack and pinion. In working it the valve G of the cylinder was 

 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 imperfect 

 at best. 



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 Fapin'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 



