SIX WILLIAM SIEMENS, F.R.S. 285 



accuracy they required, without refining on other part* that have 

 only to be strong, to resist the rough usage to which the meters are 

 subjected when taken in use. 



The calcareous matter in water deposits only on the surfaces of 

 brass that are not exposed to the current. It exercises therefore 

 no effect on the measuring surface, but if allowed to penetrate into 

 the chamber of the counter it incrusts the small wheels and 

 spindles, and causes them to break or wear rapidly. To alleviate 

 this, the first chamber F is separated completely from the interior 

 of the meter, excepting the capillary space between the upright 

 spindle and its bearing, through which the pressure in the pipes is 

 transferred to the chamber, but which is too narrow to allow of an 

 intermixture of fluids. This chamber is filled, before it leaves 

 the manufactory, with pure olive oil, which affords a complete 

 and continuous protection to the reducing wheels. The upper 

 chamber of the counter is not under the pressure of the water, 

 and contains atmospheric air. The differential motion between 

 the wheels Y and Z, of 101 and 100 teeth respectively, produces 

 a reduction of 100 to 1, or 100,000 to 1000, indicated upon a 

 single circle of divisions, whereby the use of the meter is much 

 facilitated. 



For meters of less than two-inch diameter of supply pipe, the 

 spiral form of propeller, or Barker 's-mill arrangement, is adapted, 

 except in cases where the water acts impulsively, as for instance, 

 in supplying steam boilers by means of pumps, where the double 

 screw meter is the only one applicable. Fig. 7, Plate 27, is a 

 sectional representation of a spiral meter, intended for a half-inch 

 supply pipe. 



The water enters the meter through the pipe N, and traversing 

 a cylindrical grating H, covered with wire gauze, it passes down- 

 ward through the funnel K, into the propeller E, and issuing from 

 two apertures of its circumference it passes into the chamber P, 

 and thence into the exit pipe Gr. 



The propeller is formed of two discs of metal, which are bulged 

 upward, the upper one to form a funnel, fitting loosely over the 

 inlet K, and the lower one to join to an upright spindle I. The 

 two discs are joined by two spiral blades, as shown in plan in 

 Fig. G, Plate 26. At the bottom of the propeller a chamber C is 

 formed, that is filled with oil through apertures and Q, and 



