THE KINEMATICS OF MACHINERY. 



109 



good reason, for its motions are very strange, and its analysis 

 apparently very complex. 



The engine I refer to is shown (in one form) in Fig. 23. It 

 is known as the " disc engine." It was brought a good deal 

 into notice in 1851, and for a few years was used in the 

 Times office without any ultimate success. Analysis shows 

 that it is based upon the same chain as the Hooke's joint, 

 the conic chain, namely, in which three out of four links 

 subtend right angles, and of which the formula is (0-*-$ C 1 -)*. 

 The fixed link is, however, d, while in Hooke's joint 



FIG. 23. 



a (the acute-angled link) is fixed. Patents have been taken 

 out also for disc-engines in which a and others in which 6 

 is the fixed link. 



I may say, in conclusion, that while it may be impossible 

 for many educational institutions in this country to possess 

 themselves of models so perfect in execution, and therefore 

 so expensive, as those which have been sent to the Loan 

 Collection, it is yet quite practicable to construct many of them 

 in a form which, while quite cheap, is yet well adapted for 



