ed by the escape of hot gases in the ventilating-pipe, sends both
the air and the gas to the flame already highly heated. The result is
said to be admirable as regards ventilation, steadiness and power of the
light and economy of gas.

"With these lamps the pressure of the gas-current is of great
importance; and I now turn to that subject. It is a general complaint in
buildings whose rooms are high that the flow of gas on the lower floor
is deficient, while on the upper floors there is a greater supply than
is necessary. This inconvenience arises from the upper stories being
subjected to less atmospheric pressure than the lower, every rise of ten
feet making a difference in the pressure of about one-tenth of an inch
of water; and, consequently, a column of gas acquires that amount of
pressure additional. The following table, recording an experiment of Mr.
Richards, will show the result in respect to light:

Gas issuing from the burner at a pressure of--
1/10 inch of water gave the light of 12 candles,
5/10 " " " " " " " 6 "
10/10 " " " " " " " 2 "
40/10 " " " " no appreciable light.

Suppose a building of six floors is supplied from the gas-mains at a
pressure of six-tenths, and that the difference of altitude between the
highest and lowest light is equal to fifty feet: the gas in the highest
or sixth floor will issue from the burners at a pressure of
eleven-tenths; the fifth floor, at ten-tenths; and so on. In order to
secure an entirely equable flow and economical light a regulator is
necessary on each floor above the first. The gas companies are
frequently obliged to supply mills at a much greater pressure than is
stated above as necessary, in order that the ground floors may have
sufficient light."

"How about incorrect meters?" asked the traveller.

"Little need be said of them, as they fall within the domain of the
companies and the public inspector of gas. Under favorable conditions
gas-meters will remain in order for ten years or more; and when they
become defective they as often favor the consumer, probably, as they do
the gas company. Their defects do not often occasion inconvenience; and
when they once get out of order they run so wild that their condition is
soon detected, when the errors in previous bills should be corrected by
estimate of other seasons."

"You haven't mentioned the apparatus (carburetters) for increasing the
richne