GAS-METER. 123 



revolution. It is evident, therefore, that the gas must enter any chamber 

 having its inner hood above the surface of the water. 



B C D E represent the inner hoods, and the direction of the gas from the 

 inlet-pipe is shown by the small arrow at B. As the chamber fills with gas, 

 it displaces the water, and causes the drum to revolve. Before B dips into 

 the water, the hood C rises above the surface, and opens a communication for 

 the gas into its chamber ; and so on with D, E, when it will have completed 

 one revolution and measured 200 cubic feet. 



The same action that allows the free passage of the gas into the chambers 

 causes it to be expelled from them through the outer hoods F G H I, in the 

 direction of the arrow at F : each of these outer hoods is sealed alternately 

 in the same manner as the inner hoods, and opened for the passage of the gas 

 from them, by one constantly being above the water-line. In setting out the 

 hoods care must be taken to have them of a proper length. The direction in 

 which the drum revolves is marked by the arrow over the top of the case. 



The bevels of the division-plates d d are arranged so that they will enter the 

 water without effort ; and, for the convenience of workmen, they are generally 

 made to slope towards the points where lines drawn at right angles through 

 the centre of the axis would intersect the inner circumference of the drum, 

 as d m, d n. The axis a a on which the drum revolves is supported on fric- 

 tion-rollers ; on the front end of this axis a spur-wheel S is fixed, working 

 into another wheel T, having half the number of teeth ; at every half revolu- 

 tion of the drum it will therefore make an entire revolution ; its spindle passes 

 through a stuffing-box, and is furnished at the opposite end with another 

 wheel V, which marks 100 feet on the index. From a pinion on the spindle 

 of this last wheel another wheel is worked, having ten times the number of 

 teeth on the pinion, which will therefore mark thousands. This last wheel is 

 again furnished with a pinion and works into a third wheel, which will mark 

 tens of thousands, and so on ; the quantities marked on the dials increasing 

 in a tenfold ratio up to hundreds of millions, or higher if thought necessary. 



The entire train of wheel-work is shown in Fig. 26, where a is the first 

 spur-wheel, working upon the main axis ; b the second wheel, both being in- 

 side the meter-case ; c is the wheel on the opposite end of the shaft of b, which 

 projects through a stuffing-box on the case, in order to communicate motion to 

 the train of wheel-work, which must of course be on the outside of the meter- 

 case ; d is the wheel driving the hand which marks hundreds on the index, 



R2 



