Page:The Kinematics of Machinery.djvu/574

 552 KINEMATICS OF MACHINERY.

the form P...J_...6 T, but becomes C7... _]_.... (7. It is carried by the link d G ... || ... G. This link Eobertson uses as the piston- rod, that is the driving-link of the chain, he omits, however, the link e C ... || ... P, so that the piston d is constrained to oscillate about its axis at the same time that it moves to and fro in the cylinder. The contracted formula of the train, unreduced, is (C"C"P- L C"C"P- L ) L , and in the form used by Eobertson, omitting I and e (putting together consecutive similar symbols),

�We need not examine here whether the machine be practically useful or not ; it serves equally well in either case as an example of empiric synthesis, which seems to be earned over all constructive difficulties in the delight of originating new mechanisms.

Robertson has used also another form of the chain for his machine, as is shown in Fig. 393. Here e only is omitted, but the arrangement of the links is at the same time somewhat altered. The formula of this chain unreduced is (C"C- L C- L P C"P- L ) t a, or more shortly, and with the reduction, (G" C^P^-C" 'P-^i e. The reader will have no difficulty in finding still other forms in which the chain (C+) can be employed. Some of these may find useful practical applications.

The seven-linked cylinder chain may be arranged constrainedly in other ways than that above mentioned, in the way, for example, shown in Fig. 394. By making one or more of the links of infinite

length we can of course obtain very numerous forms of the chain. A very interesting example of it is shown in Fig. 395, a mechanism which has been applied by Brown * as the lead- ing train of a steam engine. If I am not mistaken it had been used earlier 394 for the same purpose by Maudslay. 60

Here the link a has the form


 * +;,. /,...#+, the link I being C~ G, it consists, that is, of a

cylinder and a sphere, the centre of the latter lying upon a normal to the axis of 2 drawn from the point of insection of 2 and 1. The sphere is paired with the cross slide e.


 * Engineering, Feb. 1867, p. 158.

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