SOLID MEASUREMENTS. 235 



would perhaps like to have them described in a general way. The 

 ordinary wet gas meter is a mere cylindrical box about half full of 

 water, in which there are four vanes fastened to a horizontal spindle. 

 The gas flows in at the bottom, and as it flows in it turns the vanes 

 round, then delivers the gas into the upper part, from whence it goes 

 into the house through the supply pipe. Therefore, for each quarter 

 revolution a definite measure of gas passes in, and consequently 

 passes out. There is a counter fixed on the spindle which counts 

 the number of revolutions, and as that is done to a scale, it is read 

 off in cubic feet or hundreds of cubic feet. I have not gone into 

 any details, and I dare say the rough sketch I have made does not 

 represent it with anything like accuracy, but that is the principle. It is 

 not very satisfactory for many reasons. It regulates with tolerable 

 truth, supposing the meter is perfectly and honestly arranged ; but it 

 has the disadvantage of wetting the gas, which makes it burn badly 

 for one thing, and it also tends to deposit water in the joints of the 

 pipes and to give trouble in that way. The dry meter is very much 

 like the cylinder of a steam engine, only differently arranged. If you 

 can imagine a steam engine with the piston fixed and the cylinder 

 moveable, it would be very like it, only instead of being made of rigid 

 materials there is a bag on each side of a fixed diaphragm. The gas 

 first comes into the bag on one side, and when it is full up to a cer- 

 tain point it presses the end of it against a stop which shuts it oft, 

 and at the same time opens an out-flow cock into the house. But at 

 the same time that it shuts off the one bag it opens an inflow cock into 

 the other bag so that the other side begins to fill. Thus at every 

 half stroke one bag gets filled, and the other emptied, and at the 

 opposite stroke the first gets emptied and the second filled. Each 

 stroke is recorded on a counter which thus registers the quantity of 

 gas passing through the meter. This is in several respects a much 

 better arrangement than the wet meter. I think it is a little more 

 expensive to make, and gas companies generally prefer wet meters. 

 There is a practical reason generally attributed to them for that, 

 although perhaps unfairly. That I cannot speak about with certainty, 

 but it is generally supposed that if anything goes wrong with the meters 

 the dry meter makes an error in favour of the consumer, while the 

 wet meter makes an error in favour of the gas company, and con- 



