62 REGULATION OF MOTION BY FLY WHEELS. 



the two wheels act on each other, as may be seen 

 fig. 10., where the motion may be conveyed in any 

 direction. 



Hook's universal joint, as represented Plate 4. 

 fig. 11., maybe applied to communicate motion 

 instead of bevel-geer, where the speed is to be con- 

 tinued the same, and where the angle does not 

 exceed 30 or 40 degrees, and the equality of 

 motion is not regarded ; for as it recedes from a 

 right line, its motion becomes more irregular. 

 This joint may be constructed by a cross, as repre- 

 sented in the figure ; or with four pins fastened at 

 right angles upon the circumference of a hoop, or 

 solid ball. It is of great use in cotton mills, where 

 the tumbling shafts are continued to a great dis- 

 tance from the moving power. But by applying 

 this joint, the shafts may be cut into convenient 

 lengths, by which it will be enabled to overcome 

 greater resistance. 



REGULATION OF MOTION BY FLY WHEELS. 



In all machines, the moving power acts with 

 more or less irregularity, being sometimes stronger, 

 and at other times weaker. 



To correct this, and render the motion uniform, 

 an additional part, called 'djig, is sometimes ap- 

 plied, which is generally either a heavy wheel, or 

 a cross bar loaded with equal weights. This, 

 being made to revolve about its axis, keeps up the 

 force of the power, and distributes it equally in all 

 parts of its revolution ; for, on account of its 

 weight, a small variation in force does not sensibly 

 alter its motion ; whilst friction, and the resistance 

 of the machine, prevent it from accelerating. If 



