WATTS PLANET-TRAIN. 433
to the beam, and the wheel c fixed to the connecting-rod oscillates with it, but never turns. This mechanism of Watt is therefore a special form of the epicyclic train (CUCJ)*- Watt usually made
M
d, from which it follows that - 1
n
FIG. 284.
There is nothing here to prevent the use of an annular wheel as one of the pair c d. If this be done a becomes negative. If the outer wheel c be made the annular wheel, the value of a is always greater than unity, and the direction of rotation of d is negative i.e., it turns in the opposite direction to the frame e *.
Galloway's rotary steam-engine, now to be described, is simply a chamber-wheel mechanism formed upon a planet-train like that of Watt with an annular outer wheel.
The following three figures represent three forms given by Galloway to his engine, which he intended for screw propulsion.
- Watt himself in liis first specification mentioned specially the application
of an annular wheel in the sun and [planet gear. Muirhead, p. 50. See also Bourne's Treatise on the Steam- Engine, p. 21. K. [There is now in the Patent Museum at South Kensington a model of Watt's in which the connecting-rod end is made an annular wheel. To keep this in gear with the wheel on the shaft there is a small roller placed upon a pin attached to its lower part, and this is made to roll iipon a suitably shaped cam touching it always on the side furthest from the point of contact of the wheels themselves.]
K I P
