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SCIENTIFIC INTELLIGENCE. 



NATURAL PHILOSOPHY. 



1. Proposed Improvement of the Air-Pump. — There is rea- 

 son to think that something like Mr Watf s principle of the 

 double stroke in the steam-engine, might be advantageously ap- 

 plied to the air-pump. By this means one barrel could do the 

 work of two, which would both lessen the cost and greatly di- 

 minish friction. At first it might^be supposed that^ by this ar- 

 rangement, the management of the valves would be rendered 

 rather complicated ; but, instead of that, they would admit of 

 considerable simplification, by adopting another principle often 

 employed about steam-engines, under the name of the coffer- 

 slide valve. Suppose the barrel to be provided with a solid pis- 

 ton, moved by a rod passing through an air-tight collar. Let 

 there be two holes in the side of the barrel, one adjoining each 

 end ; and let these be covered by a sliding bar furnished with 

 four holes on its side, two being near to each end, and the whole 

 so arranged, that two of them at a time, but taken in an alter- 

 nate order, can, by a slight motion of the bar, be brought oppo- 

 site the holes of the barrel, while the other two are not, and 

 vice versa. Suppose two of the four holes, say the middle ones, 

 to be the ends of two tubes which unite in one slender wind- 

 ing and slightly flexible tube, communicating with the receiver ; 

 and let the other two be merely perforations, which may have 

 their exterior ends either quite open, or, to prevent any return 

 of air into the barrel, they might be covered with slips of blad- 

 der or oiled silk. If, then, the bar be moved up and down alter- 

 nately about the third of an inch, so as to have two of its holes, 

 one of each sort, remaining over these in the barrel, while the 

 piston moves in the one direction, and the other two remaining 

 over those of the barrel, while the piston returns in the opposite 

 direction, it is evident that we shall have, in this simple arrange- 

 ment, all the security of four metallic valves, and a single barrel 

 and piston doing the work of two. The obvious design of the 

 long flexible tube is to permit the compound valve to move 

 ■without any other joints. It might, indeed, remain fixed, while 



