334 Dr George Wilson on the Early History of the 



some share in devising the pneu- 

 matical engine. I shall call it, there- 

 fore, Hooke and Boyle's air-pump, 

 giving the former the priority as 

 the chief contriver. It consisted, as 

 Boyle said, of two principal parts, 

 *' a glass vessel and a pump to draw 

 the air out of it." Fig. 1, copied 

 from the engraving in Birch's Boyle, 

 vol. i., last page, illustrates its ap- 

 pearance and construction. The pump 

 A, had a single brass barrel about 14 

 inches in length and 3 inches in in- 

 ternal diameter. It is represented 

 apart in fig. 2, which is lettered 

 to correspond with fig. 1. It stood 

 upon a strong wooden tripod, with 

 its mouth turned downwards. The 

 piston or sucker C was solid. The 

 shank or piston-rod had teeth cut in 

 it, so as to form a rack ; and was 

 moved by a toothed wheel or pinion E 

 working into the rack, and turned by 

 a handle F, as in the air-pumps of the 

 present day. A hole was bored in the 

 side of the upper end of the cylinder, 

 provided with a plug G, which could 

 be drawn out or pushed in by the 

 hand. This was the only valve in the 

 engine. The object of the inversion 

 of the cylinder was to allow the glo- 

 bular or pear-shaped glass-receiver, 

 H, from which it emptied the air, to 

 be placed in a vertical position above 

 the pump. The receiver had a large 

 opening in the top for inserting ob- 

 jects into it. This opening could be 

 narrowed by a tight-fitting brass ring 

 1, in the centre of which was an aper- 



Fig. 1. 



Ficr. 2. 



