Manchester Memoirs, Vol. xlii. (1898), No. 0. 7 



This is the late Mr. William Froude's arrangement, 

 but an essential feature of this brake is the provision 

 which secures atmospheric pressure at the centres of the 

 vortices, and admits of the pockets being only partially 

 filled. 



The effect of the vortex motion is to ensure a greater 

 pressure towards the outside of the vortices than at their 

 centres, but, as the tangential stress is the mean pres- 

 sure over the section of the vortices, if the pressure at 

 the centres of the vortices is allowed to fall, this stress will 

 be diminished more or less. Thus, to secure regular stress, 

 it is necessary to secure regular pressure at the centres of 

 the vortices, and to obtain the maximum stress it is 

 necessary that the central pressure shall be that of the 

 atmosphere. 



In order to secure these conditions, and at the same 

 time to allow of the pockets being only partially filled — 

 that is, to allow of hollow vortices with air cores at atmo- 

 spheric pressure — it is necessary that there should be free 

 access of air to the centres of the vortices. Such access 

 cannot be obtained through the water which completely 

 surrounds these centres between the vanes and guides. 

 It is therefore obtained by passages (^in. in diameter) 

 within the metal of the guides, which lead into a common 

 passage opening to the air on the top of the case. {Figs. 2 

 and 3.) 



In order to supply the brake with water, there are 

 similar passages in the vanes of the wheel leading from 

 the box cavity within, which again receives water through 

 ports [Fig 3\ leading from an annular recess in one of the 

 disc faces of the case, into which water is led by means of 

 a flexible india-rubber pipe from the supply-regulating 

 valve. The water on which work has been done leaves the 

 vortex pockets through the clearance between the disc 

 surfaces of the wheel and the case, and enters the annular 



