

KINEMATIC MODELS. 2;5 



but because they all intersect in one point. In this particular case 



Figure 4. 



that point is at an infinite distance, but the chain moves equally wel 

 if the point of intersection be at a finite distance, as is illustrated by 

 Fig. 4. Upon this mechanism many engines (disc engines, &c.), and 

 other machines have been based. Hooke's universal joint is a familiar 

 illustration of it. The complex constructive forms of these, however, 

 make the recognition of their real nature almost impossible without the 

 aid of some such system as Reuleaux's analysis. 



In order to obtain the constrained motion of a closed pair, it is not 

 necessary that both elements should be constructed as fully as in the 

 cases we have hitherto looked at. Grooves might be cut down the 

 sides of a pin, for instance, without affecting its motion in an eye. 

 Professor Reuleaux has made some investigations, which I can only 

 mention here, on the extent .to which this process can be carried. 

 Without further proof, I have no doubt you will recognise at once that 



