SPECIAL AND GENERAL FORMULA. 273
now be written (#'. C* FA)*, the lift-wheel (C" Cz\ FA )r ;
the steamer (C'C^V^*. These last examples already show in the most distinct way the usefulness of our formula?. For the mere transcription of them is sufficient on the one hand to show the intimate connection between machines which con- structively seem to stand so far apart, and on the other hand, to indicate definitely and simply the true differences between them.
The special formulae of mechanisms are chiefly useful in the analysis of complete machines, that is, in reference to the applications of mechanisms, while the general formulae com- monly suffice for their abstract representation. Here, too, however, the special formula} are often very valuable, as showing which of the link motions is to be considered as the independent variable. We may now proceed to the systematic application of the "kinematic notation ; in the following chapters we shall have to make extended use of both kinds of formula?.
