166 TRANSACTIONS OF THE 



great accuracy whether the flow be rapid or extremely slow. It 

 has been constructed in various sizes, and is already in successful 

 use in several portions of this city. 



The water is received in a rockiuc; cup, divided in two com- 

 partments. When tilted to one side, the partition induces the 

 water to accumulate in the upper side until its gravity is suffi- 

 cient to tilt the cup and discharge the quantity thus measured and 

 weighed, and induce its accumulation on the opposite side. So 

 far, this is an old device, but to allow the apparatus to work under 

 a head and without diminishing the pressure of the water, the 

 case or vessel in Avhich the whole is enclosed, is partially filled 

 with compressed air; and to prevent the loss of this compressed 

 air by its escape through the pores of the metal, or its absorption 

 by the water, provision is made for discharging, at each movement 

 of the rocking cup, a small quantity of Vv'ater from the lower part 

 of the case, and for receiving in its place an equal volume of air 

 from the outside, which is allowed to rise through the water, as 

 represented. 



Fig. 1, is a perspective view of the whole, the upper portion 

 being of glass, to allow a view of the interior; while iig. 2 and 3 

 represent sections, on a larger scale, of the device for supplying 

 air. Fig. 4, is a vertical section of the w^hole, as ordinarily con- 

 structed of cast-iron. 



A is the pipe which supplies the water, and B a receiving 

 and retarding vessel, bolted upon the top of the main case, C. 

 This vessel serves as a kind of air chamber, and allows the water 

 to fall gently into the cup below. D is a cock, through which the 

 water is discharged, and E E is tlie surface of the water within; 

 it being understood that the air above E is at tlie density required 

 to equal tlie pressure due to the head of water. This density is 

 acquired, in the first instance, simply by the rise of the surface 

 E E, which thus compresses it. F is the rocking cup, and F the 

 partition therein. The cup being supported on suitable bearings, 

 its pivot is free to roll horizontally, to a slight extent, and thus 

 to make the resistance a rolling rather than a sliding friction. G 

 is a lever, mounted in the same trame with F, and immediately 

 below it. It is slightly bent, as described, and immediately below 



