308 APPLIED SCIENCE 



required to enable the effort produced by the first machine abed 

 to drive the second a, b l Cj d l f l . In fact, the whole first 

 machine may be considered as a somewhat complex driving 

 element, relatively to the second machine ; or the whole of the 

 second machine may be looked on as a rather complex resisting 

 element, relatively to the first machine. The two machines may 

 obviously be treated as entirely separate. Let the first machine 

 drive the second by contact between the elements b and b { and 

 between d and d r Then it is necessary that at these joints the 

 direction of the lines of bearing pressure shall be in one straight 

 line. This line is the direction of the resisting link for one 

 machine, and the driving link for the next. The joints &6 15 and 

 ee 15 between two successive machines, will be called transmitting 

 joints. They do not themselves belong to either machine. 

 Distinct elements may be introduced between the two machines 

 as in the typical example, Fig. 28. Here the second machine is 

 tied to the first by two links, each lettered / and e r These 

 elements, which must represent forces in one straight line, may 

 be considered as equivalent to the driving element of the second 

 machine, and the resisting element of the first. In the example 

 given it would be necessary to make / a tie, so that the machine, 

 as drawn, would only work when element e was expanding. In 

 another case, one part of the link / might be omitted as between 

 be and a^, and replaced by a transmitting joint between b and 

 fcj as above. An element placed between two machines and 

 serving to transmit the power, will be called a transmitting 

 element. We see then that the communication of power can be 

 made from one complete machine to another, either by two 

 joints, by two elements, or by a joint and element. We may, 

 with perfect propriety, give the name of complete machine to 

 any one of a series, each of which drives its successor ; for we 

 may regard the driving system simply as a more or less complex 

 driving element, and the driven system as a more or less com- 

 plex resisting element. We are not concerned with the complex 

 play of forces which produces the driving or resisting effort, but, 

 so far as each complete machine is concerned, only with the fact 

 that its elements are driven or resisted in a manner which may 

 be represented by a single driving or misting link. 



24. Compound Machines with one common element. The 



