62 



MECHANICS. 



be produced at whatever angle it is in- 

 clined to the horizon, provided it be per- 

 pendicular to the axis of the screw. 

 Fig. 114. 



Fig. 116. 



Hookes universal joint is a very sim- 

 ple and effectual method of transferring 

 rotation from one axis to another. 



The single universal joint is repre- 

 sented in Jig. 115. A and B are the 



Fig. 115. 



shafts, between which the rotation is 

 transmitted ; C D, E F is a cross of 

 metal, the eiids of which turn freely in 

 bushes placed in the extremities of two 

 diameters in which the shafts* terminate, 

 h From considering this arrangement, it 

 is evident that, when the shaft A is 

 turned round, the shaft B will receive 

 a similar motion. If, however, the 

 angle under the shafts A and B be less 

 than 140, this will fail to act. 



In this case, the double universal 

 joint must be resorted to. This is re- 

 presented in Jig.\\&. There are here 

 two crosses, the extremities of which 

 move on pivots, like the former. This 

 will serve when the angle contained by 

 the shafts is less than 140. 



These joints may also be constructed 

 with four pins, f.stened at right, angles 

 upon the circumference of a hoop, or 

 solid ball. They are of considerable 

 use in cotton mills, where Hie tumbling 

 shafts extend to a great distance from 



the impelling power ; for, by ap 

 an universal joint, the shaft may e cut 

 into convenient lengths, and be thus 

 enabled to overcome a greater resist- 

 ance. 



(113.) To convert a continued circular 

 motion into a reciprocating circular mo- 

 tion, or vice versa. 



There are various methods of mak- 

 ing this change. One of the most 

 common is by a crank, connected by a 

 rod with the end of a working beam, or 

 lever, as represented in fig. 87. Here 

 the end of the rod connected with the 

 crank moves with a continued circular 

 motion round the axis of the crank, 

 while the other end, connected with the 

 beam, moves alternately in a circular 

 arc. 



Another contrivance for this purpose 

 is represented in Jig. 117, where B and 



C are two spur-wheels on the same 

 shaft, and A is a crown-wheel, which 

 is only partially furnished with teeth, 

 and placed on a shaft at right angles to 

 D E. The shaft D E, being turned 

 constantly in the same direction, so 

 long as the teeth of the wheel A are 

 engaged with those of B, the shaft of 

 A is turned in one direction ; but when 

 they begin to be acted upon by those 

 of C, it is turned back in the opposite 

 direction, and so the alternate rotatory 

 motion is continued. 



It may also be effected by a wheel 

 having wipers on its circumference, 

 which raise a lever placed at right 

 angles to the plane of the wheel, the 

 lever descending by its own gravity. 



