AMERICAN INSTITUTE. 167 



it is a cross-bar, H, which regulates the extent to which either 

 end of the lever G may be depressed. The centre of gravity of 

 the rocking cup F, is at the point indicated by the star, in fig. 4, 

 and its motion with the vibration of F, is a curve, as represented- 

 by the short dotted line. The centre of gravity is thus lower at 

 either extremit}' of its motion than at tlie middle of its vibration; 

 and, in short, by well known laws, tlie cup inclines with a certain 

 uniform degree of force, to remain at either extreme of its motion. 

 The water received from B through the tube rei')resented, accu- 

 mulates on one side of F', until its gravity is sufficient to overcome 

 this tendency, wlien the cup rapidly tilts, and discharging its load 

 on that side, commences to receive an equal amount on the other. 

 There is no resistance to the commencement of this rocking motion, 

 except tlie gravity of the cup F and the rolling friction of the 

 support; but towards tlie close of its motion, it strii^es tlie elevated 

 end of the lever G, and deju-esses it. The devices for recording 

 the strokes, and also for receiving the air, are worked from this 

 lever, G, by the aid of the rod I; and both these operations, though 

 necessarily communicating with the exterior of tlie case, are per- 

 formed without the aid of a stuffing box of any kind. 



The tight joint required at the point where the motion is can-ied 

 out through the case, is obtained by the use of a kind of minature 

 slide valve, held to its seat by the pressure of the fluid Aviihin. 

 A hollow projection, K, extends upward from the bottom into the 

 interior of the case, A. Its interior communicates freely with the 

 atmosi:)liere, and its exterior is plane on one side and perforated, 

 as represented in fig. 2, the perforations i^eiug covered by the small 

 slide valve J. Tliis slide valve is connected by the rod I, to the 

 lever G, and consequently moves vertically on tlie ]dane surface 

 of K, at each movement of the latter. 



Tlie indicating mechanism is on tlie exterior of the case. It is 

 similar to that ordinarily employed on gas meters and the like, 

 and carries several indexes, which work on the face of corres- 

 ponding dials, as represented by R, in fig. 1. A rachet wheel on 

 the lowest and quickest shaft is operated by a pawl, which latter 

 is connected to the work inside through the rod L, which stands 

 loosely enclosed in the interior of K, and is connected firmly to 



