MECHANICS. 



rag-wheel and chain might be used, and 

 if the directions be in different planes 

 two wheels will be necessary. 



If, however, the velocities be differ- 

 ent, olher means must be resorted to. 

 If the two directions be in the same 

 plane, two racks may be worked by the 

 sectors of two wheels moving on the 

 same axle, the magnitudes of the sectors 

 being proportional to the two velocities. 

 Such an apparatus is represented in 

 fig. 98. If, however, the two directions 



>.99. 



be in different planes, the motion must 

 be transmitted from the one rack .to the 

 other by the aid of bevelled wheels. 



Rag-wheels and chains may evidently 

 be used in these cases for racks. 



(110.) To convert a reciprocating rec- 

 tilinear motion into a continued circu- 

 lar motion, and vice versa. 



The methods of producing these ef- 

 fects are very numerous. A continuous 

 circular motion will produce a recipro- 

 cating rectilinear one, if a w-heel hav- 

 ing wipers on its circumference be 

 placed in connection with a vertical 

 beam or stamper, on which a projecting 

 shoulder or pin is raised, by which the 

 beam is lifted by each wiper, and falls, 

 when disengaged from it, by the revo- 

 lution of the wheel : it is then lifted by 

 the next wiper, and so on. 



Also, if a vertical beam be terminated 

 in a rack which is connected with a 

 wheel which has teeth only on a part of 

 its circumference. While the toothed 

 part of the wheel is engaged with the 

 rack, the beam will be raised, and the 

 moment the last tooth of the wheel 

 passes the rack, it will fall. It will be 

 again raised when the teeth engage 

 the rack, and so motion is continued. 



In this case, the motion of the rack 

 in one direction is produced by its 

 weight, or that of the beam, or stamper, 

 with which it is connected. It is easy 

 to make the wheel itself produce both 

 motions in the rack. In/rg-. 99 is repre- 



sented a double rack, 



worked by a wheel par- 



tially furnished with 



teeth. As the wheel P is 



turned in the direction of 



the arrow, its teeth, be- 



ing previously disengaged 



from those of the rack, B 



D, will commence to work 



in those of A C, and 



will evidently press the 



rack down. When the 



last tooth of the wheel 



has passed the rack A C, 



this downward motion will 



cease, and the teeth will 



become engaged with those of the rack 



B D, and the rack will accordingly be 



raised ; and by continuing the rotation 



of the wheel P in the same direction, 



the rack will be alternately elevated and 



depressed. 



This may also be effected by a simple 

 method, represented in fig. 100, where 

 M N is a beam moving in guides c d 

 and ef: a b is a bar moving on joints, 

 or pivots, at a and b, and A is a wheel 

 turned by a winch A H, or otherwise. 



Fig. 100. 



. 101. 



As the wheel revolves, the bar a b is 

 evidently alternately pressed upwards, 

 and drawn downwards, and by this the 

 beam M N is moved alternately up- 

 wards and downwards between the 

 guides. 



In Jig. 101 is represented a method 

 similar to that shown in fig. 99, but 

 each rack is fuinished with but one 

 tooth. In this case the pins or teeth of 

 the wheel alternately raise and depress 

 the rack, in the same manner as in/g-. 

 99. 



A very ingenious contrivance, for 



