Chap. 9.] Invention of the Air Pump. 423 



actual vacuum might be formed. The air-pump, 

 however, was not difcovered till 1654. ' For the firft 

 invention of this, the world is indebted to Otto Gueric, 

 a German ; but it was our countryman Boyle who 

 converted it to real ufes ; it was he who improved it, 

 and applied it to philofophical purpofes. In the hands 

 of Gueric it was a mechanical inftrument j in thofe of 

 Boyle it was a truly philofophical machine. By this 

 machine we can with cafe empty a glafs veffcl of its 

 air, and put what bodies into it we think fit. Thus 

 comparing the changes wrought upon bodies by being 

 kept from air, with the fames bodies when expofed to 

 air, we require a knowledge of the effects of that fluid 

 upon bodies in general. 



As the air-pump is a machine very generally known, 

 I mall not attempt a new defcription of itj but for the 

 lake of thofe readers who are but little acquainted with 

 philofophical apparatus, take the defcription of it from 

 one of the moft popular writers on thefe fubjects, in 

 order that its conftruction may be the more eafily un- 

 derftood. 



Having put a wet leather on the plate L L (fee 

 Plate XXX. Fig. i.) place the large glafs veflel or re- 

 ceiver M with its mouth downwards upon the leather, 

 fo that the hole / in the plate may be within the glafs. 

 Then turning the handle F backward and forward, the 

 air will be pumped out of the receiver by the ac- 

 tion of the mechanifm below. As the handle F, 

 reprefented more at large (Fig. 2.) is turned back- 

 wards, it raifes the fucker or pifton de in the hollow 

 barrel B K by means of the toothed wheel E engrain- 

 ing in the toothed rack D d: and as the pifton or 

 fucker is leathered fo tight as to fit the barrel exactly, 

 no air can get between this pifton and the barrel, and 

 therefore all the air above d in the barrel is lifted up 

 E e ^. towards 



