SEBKIti-BALLJAN, WOODCOCK. 377
distant to a (curtate) peri-trochoid (cf. 22 and 23). All diameters of this trochoid passing through 1 are equal, so that the rollers upon the rod c remain always in contact with the rim, have, that is to say, a closed motion. Witty 's second machine can hardly be said to be practically useful, but notwithstanding this it was again proposed, in an almost unaltered form, by Andrew in 1858.*
Noticing the eccentric position of the axis 1 in the trochoidal ring, we see that it would not be difficult to use the link c as a piston, working within a suitably formed peri-trochoidal chamber. This has been several times done, as for example by Franchot in Paris. Fig. 3 is an outline of his machine, d is formed as a cylindric drum, c as a piston, its two semi-cylindrical ends in contact with the sides of a. Serkis-Balliaii exhibited a very similar machine in Paris in 1867. f
Woodcock combined t\vo chains in his machine, J for which the general formula is therefore 2 [(CJPJ-)? - &)], (PL XXIV. Fig. 4). The sectional profile of the chamber should again be peri-trochoidal; the block c is of fixed length and has rounded ends. According to the drawings before us, however, Woodcock made the chamber circular. Such an approximation is, of course, defective, but might work tolerably well if somewhat elastic packing pieces were used, and if the eccentricity, i.e., the length of the crank, were made very small. The latter was the case in Woodcock's machine.
Of the four machines mentioned in this section the three last have the least importance, for the peri-trochoidal pr6file does not possess any special advantages to counterbalance the constructive
- Newton, London Journal of Arts, &c., New Series vol. ix., 1859, p. 335.
t He obtained a French patent for its application as a pump, Propagation Industrielle, vol. iv., 1869, p. 241 ; as to the steam-engine, see further Ginie, Industriel, vol. xxix. 1865, p. 203.
+ Newton, London Journal of Arts. Conjoined series, vol. xxiii., 1843, p. 93.
Another engine formed from the train (C^F^Y in a way very similar to the two last is that of Hyatt, (Bourne, St.Eng., p. 132) or Wilson (Bourne, St. JEng., p. 392). Here, however, the chamber seems to have been made elliptical, or nearly so, and we are told that the working of the piston in it illustrates a "peculiar and unlooked- for characteristic of the elliptical figure," although "the true action is only to be secured when the amount of ellipticity is exceedingly slight ! " A couple of force- closed sliding pairs are used to keep the pieces which correspond to the ends of the piston c in contact (with higher pairing) with the sides of the chamber. The arrangement is of course quite worthless.
