612 NOTES.
keep it against the rim of the wheel a. We have here an application of the pair (7 Z , Q\ or (C z ,\ ) belonging to order XVI. ( 149.) The vessel F-, with which Q\ is paired on the other side, has, on account of the sliding of the water-ring, the form C-. We might write the whole train therefore :
C+... f ...0-, Qy.. b . ..Qy, C?+... | ...0+C-...||...C-
We note also again here how practical machine construction has taken the road already pointed out by our synthesis. The pairing of Q\ with C 2 is, as we know, nothing new in itself ; it exists, for instance, in the common water- wheel and other mechanisms ; the mechanism of Robertson is interesting only as an attempt to use the pairing in a free manner in a driving-train intended for common factory work.
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