ON THE MECHANICAL EQUIVALENT OF HEAT, 
307 
The internal disc faces of the brake case, as far as the pockets are concerned, are 
the exact counterparts of the disc faces of the wheel (except that there are 25 
pockets), so that the partitions in the case are in the same planes as the partitions 
meeting them in the wheel, there being inch clearance between the two faces. 
The pairs of opposite pockets when they come together form nearly closed 
chambers, with their sections, parallel to the vanes, circular. In such spaces 
vortices in a plane inclined at 45° to the axis of the shaft may exist, in which case 
the centrifugal pressure on the outside of each vortex will urge the case and the 
wheel in opjDOsite directions inclined at 45° to the direction of motion of the wheel, 
Fig. 2. 
which will give a tangential stress over the disc faces of the wheel of l!\/2 of the 
sum of these vortex pressures. The existence and maintenance of these vortices is 
insured by the radial centrifugal force of the water in the pockets in the wheels 
owing to its motion. 
This is the late Mr. W. Fuoude’s arrangement. But an essential feature of the 
brake is the provision which insures the pressure of the atmosphere at the centre of 
the vortices, even when the pockets are only partially filled. 
The vortex pressure is greatest at the outsides of the vortices, which occurs all 
over the annular surfaces of the pockets, but the actual pressure on these surfaces is 
2 R 2 
