REPULSION AND ATTRACTION. 



The pressure then between the discs, tending to 

 separate them, is limited to the atmospheric 

 pressure round the outer part, beyond the line 

 to which it is driven back, the boiler-pressure 

 over a very small area at the centre, and the 

 very moderate vertical pressure of the ex- 

 panded steam as it rushes from the centre out- 

 wards. These pressures, assisting one another 

 to separate the discs, are decidedly less than 

 the atmospheric pressure all over the outsides, 

 tending to drive them together. 



Thus the net result of the jet's action is that 

 when the discs are originally at a distance, it is 

 able to keep them at a distance, against a con- 

 siderable force tending to bring them together, 

 whereas, when they start together, it is able to 

 hold them together against a considerable force 

 tending to move them apart. 



103 



