Mil. W. M. Buchanan's Theory\of the Reaction Water- Wheel. 117 



are usually acted upon by springs carefully adjusted in tension to the 

 centrifugal force due to their weight and angular velocity. By this 

 arrangement it is easy to perceive, that if the velocity of the machine 

 be reduced by an addition of burthen, the contrifugal force will at the 

 same time decrease in a duplicate ratio ; and the springs acting as cen- 

 tripetal forces, will cause the valves to move towards the centre of 

 the machine, and thereby enlarge the orifices. And conversely, should 

 the velocity bo unduly increased by a diminution of burthen, the centri- 

 fugal force will in like manner increase in the duplicate ratio of the in- 

 crement of speed, and will consequently cause the valves to move out- 

 wards against the action of the springs, and thereby contract the orifices, 

 and allow a less quantity of water to flow through them. 



In the larger class of machines, the springs give place to a more com- 

 plex apparatus, by which the valves are worked directly by eccentrics 

 acted upon by a system of external geering. A rod *, having one end 

 heavier than the other, traverses the whole diameter of the machine, 

 passing through the projection of the eye and the boss of the shaft, and 

 carrying a vane-wheel k, at each of its extremities. The rod is free to slide 

 endlong in bearings which project above the upper surface of the machine, 

 but is retained in a given position by a spiral spring r, so long as the 

 proper velocity of the machine is maintained. But the instant that velo- 

 city is 'disturbed, the rod moves endlong, and bringing one of the vane- 

 wheels within the action of the jet from the contiguous orifice, it is made 

 to revolve round its axis in the direction of the impulse communicated 

 to the vane-wheel. This motion is transferred to the geering of the two 

 valves simultaneously, by two endless screws I, which slide by sunk-keys 

 upon the rod, and thence to the eccentrics n, within the valves, which are 

 thus made to turn in directions to contract or enlarge the orifices 

 according as the vane-wheel upon the weighted or unweighted end of the 

 rod is in action. When the velocity of the machine is unduly accelerated, 

 the spring yields to the increased centrifugal force of the weighted end 

 of the rod, and the corresponding vane-wheel is thrown into action; and 

 its operation is to contract the orifices, and allow a smaller quantity of 

 water to pass. On the contrary, when the velocity falls below the proper 

 rate, tho tension of the spring predominates, and the vane-wheel on the 

 unweighted end of the rod is brought into action ; and the effect is an 

 enlargement of the orifices and an increase of the power diroctly propor- 

 tional to the increase which takes place in the quantity of water 

 discharged. 



These and a few other constructive details which would occupy too much 

 time to enumerate, arc essential to the practical application of the machine 

 as a prime mover; but the grand technical problem — that upon which 

 the. poflitfa value of the machine mainly depends, and to which all. 

 appliances are subordinate — is the propor form of the water-channels. 

 If these be incorrectly determined, no elegance or accuracy of workman- 

 ship will render the machine effective. They cannot, it is true, by any 



