DRY GAS-METERS. 



UNDULATORY FORCES.-LIGHT. 



127 



happens to be above the level of the water. In the figure 

 it is passing from d into a. This gives a buoyancy to that 

 chamber ; and as it rises or floats, it turns the drum round 

 from right to left, causing the gas which is in the upper 

 and descending compartments to escape through their outer 

 slits into the outer chamber, and thence to the burner. 

 It will be noticed that, as the drum revolves, the 

 entrance-slits between the middle and outer chambers are 

 successively carried under the water, and that as soon as 

 this happens, the exit-slits in the circumference of the 

 drum are each in their turn brought out of it. This is 

 shown in the figure as about to occur with compartment 

 c, whose entrance-slit is just dipping under the water, 

 wliile the exit-slit is rising out of it. Since the time of 

 Air. Malam, other improvements have been effected in 

 the details of this meter ; by means of which the revolu- 

 tion of the drum has been made steadier, the amount of 

 friction lessened, and the water kept at one uniform 

 leveL Among the names of those who have devoted 

 attention to the subject, are Crosley, Wright, Evans, 

 Hulet, Smith, Paddon, and Ford ; all of whom have, in 

 some particular or another, improved the instrument. 



Fig. m. 



Figs. 127 and 128 

 represent a meter of 

 modern construc- 

 tion, with most of 

 the improvements 

 adopted. The gas 

 passes by the inlet- 

 pipe a into the 

 chamber 6, whence 

 there is a commu- 

 nication by means of 

 a flat valve with the 

 compartmente ; from 

 this it passes through 

 the Ix-nt pipe, form- 

 ing the axle of the 

 drum, into the com- 

 partment il, and 

 thence, in the manner 

 already described in Malam's meter, it gets into one or 

 other of the four compartments, and so escapes by an 

 exit-slit into the space formed by 

 the surrounding case : / is a ball 

 which floats on the water, and 

 keeps the flat valve open. If the 

 water gets below its proper level, 

 the ball falls; and by bringing 

 down the valve, shuts off the gas. 

 g is a tube for passing water into 

 the cistern, and i is a waste 

 cistern for receiving the water 

 when it gets above the proper 

 level and flows over: h is a 

 syphon-tube for drawing off the 

 water which has been added in 



A excess. By a train of wheelwork, 

 the revolutions of the drum are 

 communicated to the hands on the 

 dial-plate ; and thus the quantity 

 of gas consumed is registered. 

 There are two objections to the wet meter, which 

 are insurmountable. These are, that the instrument 

 registers the vapour of water as well as gas; ami, 

 secondly, that it is very liable to stop, at an unexpected 

 moment, by the deficiency of water and the sinking of 

 the float. When a meter is placed in a warm situa: 



uantity of aqueous vapour that is registered by the 

 iinient, and set down as gas, is very considerable ; 

 anil if it should so happen that the gas, after passing the 

 meter, has to traverse a cold locality, the aqueous vapour 

 will be recondenoed as water, and will cause a flickering 

 of the flame, or even a total closure of the pipe. 



At one time it was possible for the gas companies to 

 derive an advantage from the overfilling of the water- 

 cistern, whereby the capacity of each measuring chamber 

 was somewhat diminished; and thus a revolution of 

 the drum did not record a proper quantity of gas. It 



was also possible for the company to be defrauded by a 

 deficiency in the amount of water ; but now both of 

 these objections are guarded against by the waste-tube 

 and cistern on the one hand, and by the float- valve on 

 the other. 



It will be seen, by an examination of the meter repre- 

 sented in Fig. 126, that, by tilting the meter a little on 

 one side, the gas will pass through the slits of the upper- 

 most chamber without turning the drum at all, and 

 frauds are sometimes committed in this manner; but 

 the experiment is a very dangerous one, and is not likely 

 to be practised by any but the most determined rogue. 



The dry-meter is a more complicated apparatus, though 

 it consists in all cases of a chamber, or set of chambers, 

 with flexible leather sides. The action is very similar to 

 that of a pair of easy-going bellows ; and the movement 

 is communicated to levers and rack-work, which not 

 only register the amount of gas that passes, but, by a 

 set of sliding-valves like those of a steam-engine, they 

 also cut off the supply of gas from one chamber, and 

 turn it on into another. 



The first dry-meter was patented by Mr. Maiam in 

 1820: it consisted of a set of six bellows placed in a 

 radiating direction around a common centre, the whole 

 being inclosed in an air-tight chamber. These bellows 

 worked successively one after the other, and they com- 

 municated their motion to a set of wheels, which served 

 to register the quantity of the gas delivered. This 

 machine was, however, not perfect it had many radical 

 faults ; and hence it did not come into general use. 

 Next after this was the instrument constructed by the 

 Dry-Meter Company. The measuring chamber was 

 formed of leather, which was found to be liable to many 

 objections ; for if the meter wore used constantly, the 

 leather expanded under the influence of the gas, and so 

 it recorded against the interest of the company ; whereas, 

 if it were not used so constantly, it underwent con- 

 traction, and then it registered against the consumer : 

 besides which, the valve moved so suddenly from one 

 side to the other as to produce an unsteady flame, and 

 hence the meter was not much patronised. Sullivan's 

 meter, which followed upon this, was open to the same 

 objections ; for it consisted of two loose leather dia- 

 phragms and a rotatory valve. In 1833, an American, 

 by the name of Berry, patented an instrument winch was 

 invented by a person named Bojardin. The meter was a 

 hollow chamber, which had a movable diaphragm or 

 partition that divided it into two compartments, and, by 

 means of sliding-valves, the gas was alternately let in or 

 out of them. In 1836, Bojardin invented a still better 

 machine ; and he is looked upon as the originator of the 

 present form of dry-meter. Since that time, Mr. Defries, 

 Mr. Edge, and Mr. Croll have improved the instrument, 

 and brought it into its present condition. Mr. Defries' 

 meter contains three measuring chambers, which are 

 separated from each other by a flexible partition formed 

 of leather, and partially protected from the action of the 

 gas by four triangular metal plates, which almost diver 

 the diaphragm. This flexible partition is raised or 

 depressed by the gas, so as to form a pyramid or a flat 

 surface; and the rise and fall of the partition is com- 

 municated to the wheelwork of the apparatus ; but, as in 

 all cases where leather enters into the construction of the 

 measuring chamber, the instrument is very liable to 

 register incorrectly. The meter which is manufactured 

 by Messrs. Croll and Glover is said to be free from this 

 objection : its construction will, perhaps, be understood 

 from the following account, taken from Mr. Croll's paper, 

 which was read before the Society of Civil Engineers in 

 1845. " If we imagine a steam-engine measuring its 

 steam by the movements of the piston, we shall have 

 some idea of the principle of the instrument. The steam 

 enters the cylinder over the piston, and forces it down 

 through a certain space ; the supply is then cut off, and 

 the action is reversed. Now, suppose the piston to be of 

 a given area, and the distance through which it moves at 

 every stroke to be constant, it can readily be conceived 

 how the actual quantity of steam employed could be 

 indicated and calculated. The meter in question bears a 



