472 Scientific Proceedings^ Royal Dublin Society. 



The upper section E has a central hemispherical cavity F one inch in 

 diameter, which is surrounded by a rounded lip. The mouth of this cavity 

 is closed by a rubber diaphragm N, held in position by the lower section O, 

 when it is bolted on. 



The manometer consists of fine bore (approximately half mm. diameter) 

 thermometer tubing, approximately 60 cms. long, accurately graduated volu- 

 metrically in the upper 50 cms. The graduations are at distances 6 ram. apart 

 below, but in the upper 20 cms., wliere the pressure changes more 

 rapidly in proportion to the rise of mercury, the divisions are more closely 

 set (0'5 mm. apart). 



The manometer is secured to the casting -E^by thescrewing-gland B. This 

 has a hexagonal head, by means of which it can be screwed firmly down on 

 the rubber bung D, making a firm pressure-tight joint. 



A metal washer C is placed between the gland and the rubber to 

 diminish friction. The manometer is connected with the space Fby a narrow 

 hole drilled through the casting. The upper part of this passage is enlarged 

 for about -|- inch to give a good seating to the manometer tubing. In this 

 enlargement a thin washer of fibre, having a central hole, may be placed to 

 avoid chipping the manometer tube against the iron of the seating, though 

 in practice this was not found necessary. To facilitate the adjustments, a 

 by-pass is connected with this narrow passage. The by-pass is closed by a 

 hardened steel needle-valve (i?), which can be screwed firmly home by a tap 

 wrench. This needle-valve is shown in detail in the figure. A packed gland 

 P is fitted to prevent leakage of mercury. The by-pass is continued into the 

 steel tube 8, through wliicli mercury can be admitted or released. The lower 

 casting G has a groove turned in its upper face to fit accurately the lip of 

 the upper casting, allowance being made for the thickness of the rubber 

 diaphragm. 



"When the bolts R are screwed firmly home, the diaphragm N is held 

 absolutely pressure-tight. Into a central passage 1 inch in diameter the iron 

 plug K screws home ; the lower end of the plug carries a hexagonal head to 

 admit of tightening with a spanner. A metal disc M -f^ inch thick cross-cut 

 on both surfaces, and pierced by numerous fine holes, serves to distribute 

 water. Above this disc a disc of fine wire gauze is placed to prevent the 

 escape of the sand. The steel tubes Z, which are continued upwards by the 

 drill-holes L', serve to allow a current of water or other liquid to be kept up. 

 The flow is controlled by a tap on the right-hand tube wliile the liquid is 

 admitted through the left-hand tube under a slight pressure. Tlie top of the 

 drill-lioles D are counter-sunk, and the end of the screw-plug K is cross-cut 

 with fine channels to allow a free water passage under the metal disc BI. The 

 entire apparatus is set on a circular iron tripod. 



