217 



the machine is equally efficient with one or several compart- 

 ments open. It is least with the higher speeds, and vice versa, 

 as might be expected from the elasticity of the beetles being 

 more active in the former case ; but there is no difference 

 which cannot be explained by this cause. 



2. The quantity of water discharged in these experiments 

 is scarcely more than half what is due to the head and water- 

 way of the sluice. This was entirely unexpected; for in Bar- 

 ker's mill and other reactive wheels of the same kind, the 

 centrifugal force increases the discharge ; and nearly half the 

 whole power is thus absorbed. 



From the drawing of this turbine supplied by Messrs. Gard- 

 ner, it appears that the effective water-way of the sluice, with 

 three compartments open,* is 186 feet. From this and the 

 column 2, the velocity with which the water enters the tur- 

 bine can be computed; and Dr. Robinson finds that^when 

 the speed is seventy-two revolutions it enters without shock, 

 a condition considered by Poncelet and others, who have 

 treated of this wheel, to be essential. Here, however, the 

 maximum is at a much lower velocity ; from which it may be 

 inferred that the theory of the turbine requires in this respect 

 some modification. On the other hand, if Riihlman's details 

 and plate of the St. Bias turbine (the most remarkable that 

 has yet been constructed) are exact, it deviates from this 

 rule far on the other side, revolving with more than twice the 

 speed due to this condition. It seems, therefore, that the 

 theory of the turbine requires some revision. 



On the whole, Dr. Robinson is of opinion that the tur- 

 bine is a very valuable motive agent, even should it not fully 

 realize the highest statements of its efficiency which have been 

 made on the Continent. He has not yet been able to compare 



* At the time of these experiments tlie permanent supply of water was 

 only ten cubic feet, which will explain the diminution of fall as they pro- 

 ceeded. 



VOL. IV. 



