338 Dr George Wilson on the Early History of the 



that the receiver was not directly attached to the pump. A 

 tube H, provided with a stopcock, I, passed from the upper 

 part of the side of the cylinder, through the water-trough, in 

 a horizontal direction, along a wooden board K, covered by a 

 thick iron plate, and was then bent up so as barely to project 

 through the iron. The receiver was no longer a globe or 

 pear-shaped vessel, but a bell-shaped hollow glass jar, L, 

 which was turned with its mouth downwards, like an inverted 

 drinking-glass, and, to use Boyle's homely but expressive 

 phrase, " whelmed on upon the plate well covered with ce- 

 ment.''' This arrangement of an air-pump plate, and detached 

 bell-jar receiver, I need scarcely say, has been retained in 

 all later air-pumps. 



In the figure, the piston is represented as drawn up, lifting 

 the water with it, and leaving a vacuum below^ When the 

 piston had risen above the cylinder end of the tube H, the 

 stopcock I, was opened, and the air of the receiver allowed to 

 expand into the cylinder. 1 was then shut, the stick G 

 pulled out of the aperture F in the piston, and the latter 

 pushed to the bottom of the barrel. The air in it bubbled 

 up through F ; G was then reinserted into F, and so on as 

 before. 



The second pneumatical engine probably worked as slowly 

 as the first, for there was a valve to close or open with the 

 hand, and a stopcock to turn at each stroke of the piston. 

 The stopcock was liable, also, to be opened at the wrong 

 stroke, and the receiver, instead of being emptied of air, was 

 filled with water. Boyle amusingly notifies, that he had the 

 edge of the iron plate turned up to prevent the water wet- 

 ting the floor. In spite of these defects and liabilities to 

 mismanagement in working, the apertures admitting of leak- 

 age were much fewer than in the first pneumatical engine, 

 and the piston worked tight in the cylinder. Boyle relates 

 in his fifteenth experiment with this machine, that he raised 

 a column of water, in a tube arranged as the long gauge of 

 the modern air-pump is, of more than thirty -three feet. This 

 would still be considered an excellent result with all but the 

 very best air-pumps.* 



• A Continuation of New Experiments, &c., p. 45 ; or, Birch's Boyle, vol. 

 iii., p. 207. 



