As coal-gas enters each house it is made to pass through an iron box called a gas-meter. Within this box are wheels, which are turned by the gas; and connected with the wheels, but on the outside of the box, are three dials, on which is recorded the number of cubic feet of gas entering the house in any given time. The figures on the left-hand dial stand for hundreds of thousands, those on the middle dial for tens of thousands, and those on the right-hand dial for thousands of cubic feet. To read the index, put down the figure next behind the pointer on each dial, and add two ciphers. In this way, if the index is found to record 16,700 cubic feet of gas, and at the next examination it records 18,300 cubic feet; then by subtracting we find that 1,600 cubic feet of gas has passed through the meter in the interval.-Gasometer, a large tank for holding gas.