SMYTH, EAMEY, THOMSON. 427
If we make the mean angular velocity ratio of the two wheels a and d=l, then the non-circular axoids will cause any pair of radii of the wheels to have a relative oscillatory motion, while both are turning continuously in the same direction. Then if two sectors connected with the wheels be enclosed in a chamber formed from the frame e, we can use them as pistons ; we can pair them, that is to say, with a pressure-organ, either as driven or driving bodies. The relative motions of the two pistons will then be very similar to the motion of those in Fig. 4, PL XXI. As a few examples among many, I rnay mention Smyth's rotary steam- engine, patented in 1838, which had non-circular wheels of com- plex form ;* Ramey's high-pressure ventilator with four equal elliptic wheels ;( and Thomson's steam-engine, with four equal oval wheels, of which two examples were shown at Paris in 186 7.+ The constructive difficulties connected with these machines, especially when they are intended to serve as steam-engines, are so great as to deprive them of practical importance. The outer surfaces of the pistons at least, however, can be made steam-tight, as they form a cylinder pair with the chamber. Ramey's ventilator is said to have given good results.
105. Epicyclic Chamber-wheel Gear.
I have still one other kind of chamber-wheel gear to analyse, one of which the nature has never hitherto been understood. Even the inventor himself, Galloway, does not seem to have known it, judging, at least, from his own description of the con- nection between his machine and others. In order to make our investigation complete it will be necessary to begin somewhat far back.
By placing the simple train of spur-wheels (C t C') with which we commenced this part of our analysis ( 94), upon one or other of the wheels instead of upon the frame, we can obtain two mechanisms, (C f Cy and (C X C^, besides the one (C z Cy already
- Newton, London Journal of Arts, &c. Second Series, vol. ix. 1834, p. 152.
t Gtnie Industriel, vol. xxx. 1865, p. 254.
J Rapports du Jury International, vol. ix., p. 81 ; Propagation Industrielle, vol. iv. 1869, p. 339; Chambers' s Ency. , 1st. Ed., art. " Steam-Engine. " Bataille and Jullien, Machines a Fapeur, vol. i., 1848-9, p. 431.
