Dr G. Wilson on the Early History of the Air-Pump. 331 



fully authenticate them : on the other hand, I do not know 

 any work which gives an accurate account of the early his- 

 tory of the English air-pump ; yet the records of the latter 

 are certainly not inferior in interest to those of the early 

 German air-pump, and would form a larger and more im- 

 portant chapter in a general history of the invention and its 

 application. I have thought it, accordingly, desirable to en- 

 deavour briefly to correct some of the errors into which the 

 historians of the English air-pump have fallen. 



It is in connection with the double-barrelled air-pump 

 that the accepted history of the instrument is chiefly erro- 

 neous ; but the mistakes made, in reference to the more 

 complex engine, have ultimately involved in confusion even 

 the authentic records of the steps by which the earlier single- 

 barrelled air-pump was improved. It is impossible, accord- 

 ingly, to avoid tracing, step by step, the alterations by which 

 the instrument was early brought to a state of no inconsider- 

 able perfection. Those steps, however, were few ; not more, 

 indeed, than three, or at most four. It will conduce to per- 

 spicuity, to state at once dogmatically what those successive 

 improvements were, and when they were made. 



The history, then, of the English air-pump admits of a 

 simple and natural division into four stages, three of which 

 belong to the seventeenth century, and the fourth to the 

 eighteenth. They are as follow, the dates, as given in the 

 original authorities, being according to the old style. 



1659. The construction of a pneumatical engine, consist- 

 ing of a single-barrelled pump, with a solid piston moved by 

 a rack and pinion, and a globular glass receiver directly 

 communicating with the cylinder, which had an aperture in it, 

 closed and opened by a plug moved by the hand, and playing 

 the part of a valve. 



1667. The separation of the glass receiver from the 

 cylinder, and introduction of the air-pump plate, on which 

 bell-jars could be placed and used as receivers. The pump 

 was still single-barrelled, and wrought by a rack and pinion, 

 but with an aperture in the piston, instead of in the cylinder, 

 furnished with a moveable stopper. 



1676. The introduction of a double-barrelled pump, with 



