But that was not his reaction at all. The more one reflects
upon the problem, Sylvester continued, he "wonders the more that it was
ever found out, and can see no reason why it should have been
discovered for a hundred years to come. Viewed _a priori_ there was
nothing to lead up to it. It bears not the remotest analogy (except in
the fact of a double centring) to Watt's parallel motion or any of its
progeny."[46]

[Footnote 46: Sylvester, _op. cit._ (footnote 41), p. 181.]

It must be pointed out, parenthetically at least, that James Watt had
not only had to solve the problem as best he could, but that he had no
inkling, so far as experience was concerned, that a solvable problem
existed.

Sylvester interrupted his panegyric long enough to enumerate some of the
practical results of the Peaucellier linkage. He said that Mr. Penrose,
the eminent architect and surveyor to St. Paul's Cathedral, had "put up
a house-pump worked by a negative Peaucellier cell, to the great
wonderment of the plumber employed, who could hardly believe his senses
when he saw the sling attached to the piston-rod moving in a true
vertical line, instead of wobbling as usual from side to side."
Sylvester could see no reason "why the perfect parallel motion should
not be employed with equal advantage in the construction of ordinary
water-closets." The linkage was to be employed by "a gentleman of
fortune" in a marine engine for his yacht, and there was talk of using
it to guide a piston rod "in certain machinery connected with some new
apparatus for the ventilation and filtration of the air of the Houses of
Parliament." In due course, Mr. Prim, "engineer to the Houses," was
pleased to show his adaptation of the Peaucellier linkage to his new
blowing engines, which proved to be exceptionally quiet in their
operation (fig. 25).[47] A bit on the ludicrous side, also, was
Sylvester's 78-bar linkage that traced a straight line along the line
connecting the two fixed centers of the linkage.[48]

[Footnote 47: _Ibid._, pp. 182, 183, 188, 193.]

[Footnote 48: Kempe, _op. cit._ (footnote 21), p. 17.]

[Illustration: Figure 25.--Mr. Prim's blowing engine used for
ventilating the House of Commons, 1877. The crosshead of the
reciprocating air pump is guided by a Peaucellier linkage shown at the
center. The slate-lined air cylinders had rubber-flap inlet and exhaust
valves and a piston whose periphery was formed by two rows of brush
bristles. Prim's machin