6 Reynolds and Moorby, Equivalent of Heat. 



a brake case (or brake) which encloses the wheel, the 

 shaft passing through bushed openings in the case, which 

 it fits closely so as to prevent undue leakage, while leaving 

 the shaft and brake wheel free to turn in the case, except 

 for the slight friction of the shaft. {Figs, i, 2, and 3.) 



The outline of the axial section of the brake wheel 

 {Fig. 3) is that of a right cylinder 4in. thick. The cylinder 

 is hollow — in fact, made of two discs bolted together, 

 which form an internal boss for attachment to the 

 shaft, and also meet together at the periphery — forming a 

 closed annular box, except for apertures to be further 

 described. In each of the outer disc faces of the wheel 

 are 24 pockets {Fig. 2) carefully formed, 4j^in. radially, 

 i^in. axially, but so inclined that the narrow partitions 

 or vanes (^in. thick) are nearly semicircular discs inclined 

 at 45^ to the axis ; those in one of the disc faces being 

 perpendicular to the opposite vanes in the opposite face. 



The internal disc faces of the brake case are the exact 

 counterparts of the disc faces in the wheel (except that 

 there are 25 pockets), so that the partitions, or guides, in 

 the case, are in the same planes as the vanes meeting them 

 in the wheel. The clearance between the two faces is ^^n. 



The pairs of opposite pockets when they come together 

 form nearly closed chambers, having sections, parallel to 

 the vanes, nearly circular. In such spaces vortices inclined 

 at 45^ to the axis of the shaft may exist, in which case 

 the centrifugal pressure on the outside of such vortices 

 will urge the case and wheel in opposite directions inclined 

 at 45 '^ to the direction of motion of the wheel, which will 

 give a tangential component stress over the section of 

 the vortices, between the wheel and case, of ij J2 oi 

 the sum of the pressures in the vortices. 



The existence and maintenance of these vortices is 

 ensured by the radial centrifugal force of the water in the 

 pockets of the wheel owing to its motion. 



