214 



above, 15'75 inches ; and that on the turbine thirteen inches, 

 the water being dammed up by the overfall. The brake made 

 nineteen revolutions in seventy-five seconds, equivalent to 70*1 

 of the turbine, or 23-59 of the wiper beam, per minute. 

 Hence Dr. Robinson computed 



Q=9-41; Power= 12-38; £=10-17; and p= 0-821. 



The last number, the ratio of the work done to the power, 

 is evidently the measure of the value of the machine, and 

 though it is very high, Dr. Robinson is confident that it is 

 not overrated. 



The second trial was intended to observe the effect of a 

 higher speed, and showed a remarkable diminution of effect. 

 There ^F=224lbs.; ir= 5-125 inches; the depth above 11-75 

 inches ; that on the turbine the same as before ; and the speed 

 nineteen in sixty-six seconds, equivalent to 79-6 of the tur- 

 bine, or 26-81 of the wiper beam. These data give: 



Q= 10-59; P= 14-43; £"=9.61; andp= 0.667. 



At a third experiment the brake came off the shaft, but, 

 fortunately, without doing any harm to the workmen ; and Dr. 

 Robinson did not think it prudent to replace it. He, however, 

 hopes to repeat these trials, with a brake of larger dimensions, 

 on another turbine that is in process of construction. 



The great loss of effect by increasing the speed induced 

 Dr. Robinson to suspect that some error must have occurred ; 

 but Mr. Kirk had observed that, by varying the number of 

 engines, and counting the revolutions in each case, more 

 work seemed to be performed at slow speeds. This was tried 

 with the addition of the same overfall, to ascertain the power 

 expended in each trial, and the results obtained, though not 

 absolute measures, appear to Dr. Robinson worthy of notice, 

 as they may assist the theory of these machines. The mea- 

 sures of the power, however, differ from the preceding, as the 



