11G Mr. W. M. Buchanan's Theory of the Reaction Water- Wheel 



obtained between the machine and the snpply-pipe — thereby effectually 

 removing ono of the chief practical difficulties experienced by the con- 

 tinental engineers ; and which, perhaps more than any other, led to the 

 abandonment of the machine of Prof. Segner in Germany, and of M. 

 D'Ectot in France. 



An obvious and essential advantage resulting from the admission of the 

 water into the machine on the under side, and which gave occasion for 

 the contrivance described, is the facility thereby afforded of counterpois- 

 ing the superincumbent weight of the machine by means of the hydrostatic 

 pressure due to the particular head of water employed. The pressure 

 being directed upwards with a known intensity upon a given horizontal 

 area ; and the area of the central opening being fixed in every case by 

 the volume of water and the height of fall to be employed — conditions 

 which determine the size of the machine — the weight can generally be 

 adjusted to equipoise it. It rarely happens that any difficulty is experi- 

 enced in making the machine sufficiently light for the fall under which it 

 is intended to act ; but it not unfrequently occurs that the fall, and 

 therefore the pressure, is so great, that the machine would become un- 

 wieldy were it made of equivalent weight. In cases of this kind an arti- 

 fice is resorted to, by which a part of the upward pressure is received 

 upon a fixed saucer-shaped disc g, projecting from the mouth-piece by a 

 hollow stem, and forming at its circular edge — which meets the internal 

 surface of the upper plate of the machine — a water-joint, in every respect 

 similar to that formed by the coincidence of the mouth-piece with the mar- 

 ginal edge of the central opening. This disc is made of sufficient area to 

 countervail the excess of the upward pressure of the fluid over the proper 

 weight of the machine, and consequently increases relatively with the 

 height of the fall. The small quantity of water which passes the joint is 

 allowed to escape by the hollow stem descending from the disc into a 

 transverse pipe h, cast in the rising-ring of the mouth-piece, and opening into 

 the atmosphere. 



This contrivance enables the highest falls to be equipoised without in- 

 conveniently increasing the weight of the machine, and with the same 

 facility as those of moderate height. 



To this brief indication of the technical appliances by which the ma- 

 chine has been brought to the condition of a hydraulic mover of the first 

 class, in respect of efficiency, it may be well to add that, in most cases, 

 the operations of the factory to be impelled require that the mover be 

 provided with governing apparatus, by which its motion may be rendered 

 uniform under variations of burthen. This condition is fulfilled by render- 

 ing the centrifugal force generated by the angular velocity of the machine, 

 subservient in adjusting the size of the orifices to the increase or diminu- 

 tion of power which, for the time, may be required. The extreme por- 

 tions of the inner curves of the water-channels are made detached, and 

 constitute valves which move parallel to the plane of diameter in which 

 the channels terminate. In the smaller class of machines, these valves 



