APPLICATION OF GRAPHIC METHODS 309 



compound machines described in the last paragraph have no 

 elements common to two simple machines, but we may have 

 compound machines in which either one or two elements are 

 common to two successive machines. The examples most com- 

 monly met with in engineering practice are those in which there 

 is one common element, namely, the framework or support 

 which is continuous and common to a series of successive com- 

 plete machines. The common element is necessarily in equi- 

 librium under the whole series of stresses to which it is subject, 

 but this equilibrium is not a matter of great interest. The 

 driving link of the first machine usually abuts at one end 

 against the common element. If the first simple machine stood 

 alone, one end of its resisting link would abut against the san.e 

 element ; when it drives a series of machines, the resisting link 

 of each must be so placed that in each case, if that particular 

 machine were the last of the series, the resisting link would 

 also abut against the common element. The common element 

 takes the place of one transmitting joint or one transmitting link . 

 in the types given in the last paragraph. A practical example 

 will serve to show the connection between successive complete 

 machines, having one element in common. In Fig. 29, p. 310, 

 a horizontal engine is shown driving a train of machinery. 

 The engine consists of the elements abode. The element d is a 

 fixed bed-plate ; the element c comprises a fly-wheel and spur- 

 wheel, which drives the pinion which is part of g ; the spur- 

 wheel of g drives a pinion which is part of h . A pulley, which 

 is also part of h, drives a belt 7, which, in its turn, drives a 

 pulley ra ; a second pulley, also part of 777, drives a second belt 

 and pulley n and o. A piece of wood, forming part of o, is 

 being turned by a tool which forms part of d. We have here 

 three complete machines 1st, the engine; 2nd, the machine 

 ylid, driven by two transmitting joints and gdcg, and driving a 

 transmitting link I ; 3rd, the machine mnod, driven by the 

 transmitting link / and the joint md, and overcoming the useful 

 resistance at the joint od. All these machines have the element 

 d in common. The dynamic frame of the compound machine is 

 shown in Fig. 29a,and the reciprocal figure for that frame in Fig. 

 296. The driving element of the first machine is the steam 

 which abuts against d, the bed plate or support. The resisting 



