GAS-METER. 125 



neglected, speak for themselves, and the men whose duty it is to look after 

 them will be to blame. 



It is thus constructed : in the centre of the " dial-field " a circular plate 

 is fixed, connected to the train of indicating wheel-work, and made to re- 

 volve in a certain ratio to the quantity of gas registered by the meter. Upon 

 this plate a sheet of paper is secured, divided, for example, into twenty- 

 four parts, which parts may be subdivided. Suppose the meter to register 

 300,000 cubic feet in twenty-four hours, and the plate connected by wheels 

 in the ratio of three to one to that index which marks a hundred thousand in 

 one revolution, it is evident that the distance travelled by one of the twenty- 

 four divisions of the plate from a certain fixed point will indicate the quan- 



300 000 



tity of gas made in one hour, or ^- = 12,500 cubic feet. Above this 



divided disc is a time-piece, to the minute-hand of which is attached a detend, 

 furnished with a pencil made to press gently upon the disc by a light spring. 

 As the minute-hand of the time-piece revolves, the pencil, by means of a 

 guide fixed to the meter-case, is regulated, so that in the first half-hour it will 

 make a vertical line upon the paper, in length equal to the diameter of the 

 circle formed by the minute-hand, measured from the centre to the point on 

 to which the detend is fixed ; in the second half-hour the line will be retraced 

 by the hand rising again. This is supposing the divided disc to be sta- 

 tionary ; but as it revolves in the manner previously described, the pencil 

 will make a series of curved lines, meeting the divided circle of the disc every 

 hour, and the distance travelled from point to point will mark the number 

 of cubic feet of gas made during every hour of the twenty-four. If the pro- 

 duction of gas is regular, the figures formed by the pencil will be regular 

 also : if, on the contrary, any negligence has occurred, the irregularity of the 

 figure will detect it, pointing out the hour and the amount of difference ; 

 because, if the speed of the revolving disc be decreased, the figure formed 

 will approach nearer to the straight line ; if increased, the points of inter- 

 section upon the divided circle will be further apart. 



By reference to the diagram (Fig. 27.) I think the " tell-tale " will be un- 

 derstood. 



a is the divided disc upon which the curved line formed by the pencil is shown. 

 6 is the train of the wheel-work connected with the index marking 100,000. 

 c is the time-piece and point at which the detend is attached to the minute-hand. 

 d is the detend, to the lower extremity of which the pencil is attached. 



