ron
furnaces. Many wilder dreams than this have come true in the science of
engineering; and the realization has brought honor and fortune to the
dreamers, as you must all know. The history of engineering is full of the
realization of "dreams," which have been denounced as absurdities by some
of the best living authorities.

* * * * *

THE GAS METER

The gas meter was invented by Clegg in 1816. Since that epoch no essential
modification has been made of its structure. Fig. 1 shows the principle of
the apparatus, _mnpq_ is a drum movable around a horizontal axis. This is
divided by partitions of peculiar form into four vessels of equal
capacity, and dips into a closed water reservoir, RR'. A tube, _t_, near
the axis, and the orifice of which is above the level of the water, leads
the gas to be measured. This latter enters under the partition, _l'm_, of
one of the buckets, and exerts an upward thrust upon it that communicates
a rotary motion to the drum. The bucket, _l'mi_, closed hydraulically,
rises and fills with gas until the following one comes to occupy its place
above the entrance tube and fills with gas in turn. Simultaneously, as
soon as the edge of each bucket emerges at _e_, the gas flows out through
the opening that the water ceases to close, and escapes from the reservoir
through the exit aperture, S. The gas, in continuing to traverse the
system, is thus filling one bucket while the preceding one is losing its
contents; so that, if the capacity of each bucket is known, the volumes of
the gas discharged will likewise be known when the number of revolutions
made by the drum shall have been counted. The addition of a revolution
counter to the drum, then, will solve the problem.

[Illustration: THE GAS METER.]

The instrument, as usually constructed, is shown in Figs. 2 and 3.

The reservoir, RR' contains the measuring drum, _mmmm_, movable around the
horizontal axis, _aa'_. The gas enters at E, passes at S into an opening
that may be closed by a valve, and is distributed through the box, BB',
which communicates with the reservoir through an orifice in the partition,
_hh'_. This orifice is traversed by the axle, _aa'_. The box, like the
reservoir, contains water up to a certain level, _r_. Through a U-shaped
tube, _lnl'_, the gas passes from the box, BB', into the movable drum,
sets the latter in motion, and makes its exit at S. In order to count the
volume discharged