Directions how to do this will therefore be found useful. A gas-meter
has three dials marking tip to 100,000 feet, 10,000 feet, and 1,000 feet
respectively. The figures on the second dial are arranged in opposite
order from those on the first and third dials, and this often leads to
an error in reckoning. However, there should be no trouble in setting
down the figures indicated by the pointer on each dial. We first set
down the figure indicated upon the first dial in the units place of a
period of three places, then that indicated upon the second dial in the
tens place, and then that indicated upon the third dial in the hundreds
place. To these we add two ciphers, to obtain the number of feet of gas
that has been burned since the meter was set at zero on the three dials.
From this number we subtract the total of feet burned at the time when
the preceding gas bill was rendered. This is generally called on the
bill "present state of meter." The result of the subtraction will be
the amount of gas that has been burned since the last bill was rendered.
For example:

95,300, amount indicated on dial.
82,700, amount marked "present state of meter" on preceding gas bill.
------
12,600, amount of gas for which current bill is rendered.


Equal care must be exercised when kerosene is used for illumination,
since, while it is not so dangerous directly to life, it is the chief
source of the destruction of property. Accordingly the nature of
kerosene and the way it illuminates is a profitable subject of study if
we would prevent destructive fires. Really, we do not burn the oil, but
the gas that arises from the oil when liberated by the burning wick and
becomes incandescent when fed by the oxygen of the air. While kerosene