168 TRANSACTIONS OF THE 



the slide valve J, at the point K', fig. 2. This connection avoids 

 the necessity for a stuffing box. 



When the valve J, is in its lowest position, the water in its 

 interior escapes through the aperture K'", and air from the inte- 

 rior of K flows in through the aperture J, to supply its place. 

 Now when, by the means described, the valve J, is raised to its 

 highest position (that represented in the figures) the air freely 

 escapes from the interior of J througli the cavity J', and water 

 finds access through side openings, imperfectly represented by 

 dots, so as to flow in through J". At each movement of G, there- 

 fore, the indicating apparatus, R, shows that water has been dis- 

 charged from the cup, F, and also allows a quantity of air to rise 

 in bubbles through the water, as shown in fig. 4. 



The various pipes and cocks connected to the base of the case, 

 C, serve to draw water therefrom in the usual manner. They 

 may discharge it directly at the cock from which it is seen flow- 

 ing, or may lead it in the pipe represented to any distance, and 

 the whole apparatus serves as an air chamber to regulate the 

 motion of the water. 



The device for receiving air is made a little larger tha'i neces- 

 sary, in order to ensure a sufficient supply of that fluid within 

 the case. Under ordinary circumstances, no harm can arise from 

 a too great accumulation of air, as the aperture K" which obstructs 

 the water, being liigher than either of the other outlets, it simply 

 follows that if the water surface becomes too low, small quanti- 

 ties of air instead of water are discharged through the cavity of 

 the slide valve, J, and as the density of the air escaping is greater 

 than that introduced, the effect of this device is to reduce rather 

 than increase the quantum of air in the case, C; thus there is no 

 possibiiity of too much air accumulating, except under unusual 

 circumstances. In case the pressure in the street main should be 

 suddenly diminished, in consequence of the bursting of a pipe, or 

 of an extraordinary quantity being drawn out in case of a fire in 

 the vicinity, the air enclosed in C, by expanding, might force its 

 way backward into the main. To avoid this, tlie reservoir, B, is 

 arranged, as represented, so that it will receiv^e and contain any 

 air which might thus be displaced, and hold it ready for discharge 

 into the case C again, so soon as the pressure is restored. The 



