MECHANICS. 



57 



producing the same effect is repre- 

 sented in Jig. 1 02. When the pinion 

 Fig. 102. 



P has worked in one side of the rack, it 

 acts upon the teeth in the semi-circular 

 end, by which it gives the rack a slight 

 lateral motion, which is permitted "by 

 the joints a b and c d. The pinion then 

 engages the teeth of the rack on the 

 contrary side, and moves it in the oppo- 

 site direction, and so the process is con- 

 tinued. 



In fig. 1 03 is represented a eontri- 



. 103. 



machine has been applied by M. Zureda 

 for pricking holes in leather, for making 

 cards, and has also been employed in 

 the manufacture of fishing nets. 



M. Zureda has also contrived a very 

 ingenious piece of mechanism for con- 

 verting a continued circular into a reci- 

 procating rectilinear motion. A cylinder 

 rests in a fixed frame, on pivots, and is 

 turned by a winch, or otherwise, round 

 its axis. On the surface of this cy- 

 linder a spiral groove is cut, similar to the 

 thread of a screw. This spiral groove, 

 when it reaches the end of the cylinder, 

 meets another similar groove, which 

 traverses the cylinder in the opposite 

 direction, and which runs into the first- 

 mentioned groove at the opposite end of 

 the cylinder. A pin is passed through a 

 groove, cut through and through a 

 straight beam, which is placed over 

 the cylinder, and parallel to its length. 

 The end of this pin falls into the spiral 

 groove in the cylinder. As the cylinder 

 is turned round its axis, the pin is 

 moved along the spiral groove, so as to 

 be urged from one end of the straight 

 beam to the other, moving in the groove 

 cut through that beam. When it ar- 

 rives at the end of the cylinder, it passes 

 fi-om the spiral groove, in which it 

 moved, into that which traverses the 

 cylinder in the opposite direction ; and 

 the pin is thus moved back towards the 

 opposite end of the straight beam, and 

 so the process is continued. 



-. 104, a very simple contrivance 

 Fig. 104. 



vance for producing an alternate rec- 

 tilinear motion, by a' continued circular. 

 A B is a wheel turned by a winch or 

 otherwise, and bearing, in the manner 

 of a crown-wheel, teeth, the form of 

 which may be adapted to the circum- 

 stances of the case. A rod, a b, plays 

 in guides m n, and has one end bearing 

 on the teeth of the wheel, while the 

 other end presses against a spring s. 

 As the wheel is turned, the rod is 

 forced in the direction a b by the teeth ; 

 and as it passes the top of each tooth', 

 it is forced back in the direction b a by 

 the spring. Thus the rod a b has a re- 

 ciprocating rectilinear motion. This 



