feet in diameter and 180 feet high. When
fully extended it holds 12,158,600 cubic feet of gas. Owing to its
immense size, it is built on the telescopic principle in six "lifts," of
30 feet deep each. The sides of each lift, or ring, except the topmost,
have a section shaped somewhat like the letter N. Two of the members
form a deep, narrow cup to hold water, in which the "dip" member of the
ring above it rises and falls.

[Illustration: FIG. 197.--Drawing retorts. (_Photo by F. Marsh._)]

AUTOMATIC STOKING.

The labour of feeding the retorts with coal and removing the coke is
exceedingly severe. In the illustration on p. 400 (made from a very fine
photograph taken by Mr. F. Marsh of Clifton) we see a man engaged in
"drawing" the retorts through the iron doors at their outer ends.
Automatic machinery is now used in large gasworks for both operations.
One of the most ingenious stokers is the De Brouwer, shown at work in
Fig. 198. The machine is suspended from an overhead trolley running on
rails along the face of the retorts. Coal falls into a funnel at the top
of the telescopic pipe P from hoppers in the story above, which have
openings, H H, controlled by shutters. The coal as it falls is caught by
a rubber belt working round part of the circumference of the large
wheel W and a number of pulleys, and is shot into the mouth of the
retort. The operator is seen pulling the handle which opens the shutter
of the hopper above the feed-tube, and switching on the 4 h.p. electric
motor which drives the belt and moves the machine about. One of these
feeders will charge a retort 20 feet long in twenty-two seconds.

[Illustration: FIG. 198.--De Brouwer automatic retort charger.]

A GAS GOVERNOR.

Some readers may have noticed that late at night a gas-jet, which a few
hours before burned with a somewhat feeble flame when the tap was turned
fully on, now becomes more and more vigorous, and finally may flare up
with a hissing sound. This is because many of the burners fed by the
main supplying the house have been turned off, and consequently there is
a greater amount of gas available for the jets still burning, which
therefore feel an increased pressure. As a matter of fact, the pressure
of gas in the main is constantly varying, owing partly to the
irregularity of the delivery from the gasometer, and partly to the fact
that the number of burners in action is not the same for many minutes
together. It must also be remembered