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was then shut, the stop-cock opened, and the piston as it ascended 

 condensed the air into the receiver. 



The most important points to be noticed about the earliest Eng- 

 lish air-pump, are, that it was provided with one barrel and a 

 manual valve, and that, unlike any later air-pump, the cylinder and 

 receiver were directly connected. The designation by which Boyle 

 preferred to distinguish his machine, was "Pneumatical Engine," and 

 he called it, in contradistinction to his later air-pumps, the " Great 

 Pneumatical Engine." It was presented to the Royal Society im- 

 mediately after its incorporation in 1662, and Boyle desisted from 

 pneumatic researches for some six or seven years. 



In 1667 he constructed his second pneumatical engine, as appears 

 from a letter dated, 24th March of that year, and published at Oxford 

 in 1669. with the title, '• A Continuation of New Experiments, &c., 

 &c., touching the Spring and Weight of the Air, in a letter to Lord 

 Duugarvan." Several persons supplied him with suggestions in the 

 way of improvements, of whom, however, he mentions the name only 

 of Hooke. 



The second pneumatical engine did not resemble the first in ap- 

 pearance, but, like it, had a single brass barrel. This stood with its 

 mouth upwards, in a large wooden box or trough, filled with water, 

 which rose above the mouth of the cylinder, so that the latter was 

 entirely under water. The object of this arrangement was to keep 

 the leather of the sucker or piston always wet, and therefore " turgid 

 and plump," so as to move air-tight in the barrel. The latter had 

 no valve in it. The piston which was moved by a rack and pinion 

 had an aperture passing vertically through it, which was closed and 

 opened alternately, by thrusting in and pulling out a long stick 

 managed by the hand of the operator. But the great improvement 

 and peculiarity in the engine was, that the receiver was not directly 

 attached to the pump. A tube, provided with a stop-cock, passed 

 from the upper part of the side of the cylinder, in a horizontal di- 

 rection along a wooden board covered with a thick iron plate, and 

 was then bent up so as barely to project through the iron. The re- 

 ceiver was no longer a globe or pear-shaped vessel, but a bell-shaped 

 hollow glass jar, 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 cement." 

 This arrangement of an air-pump plate, and detached bell-jar receiver, 



