Mr Bennett, A Double-Four Mechanism. 391 
- A Double-Four Mechanism. By G. T. BENNETT, M.A., 
Emmanuel College. 
(PLaTE X.) 
| [Read 24 November 1913.] 
_ §1. A plane mechanism of eight pieces may suitably be called 
a double-four when each of four pieces 1, 2, 3, 4 is lmked to all 
the four pieces 1’, 2", 3’, 4° except to I’, 2, 3’, 4’ respectively. 
_A schematic form of diagram may conveniently be drawn as in 
Fig. 1, differmg not greatly in appearance from a double-four 
of straight lines arranged in chequer fashion. Each of the eight 
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Fig. 1. 
‘pieces is represented by a triangular plate, whose vertices are 
linked by pins to three other plates. The notation to be used 
here may be described as follows. The vertex of plate 1 which is 
linked to plate 2’ will be called 12’, and the vertex of 2’ which is 
linked to 1 will be called 2’1; so that points 12’ and 2’1 coincide 
