well defined circulation.

The main feature to which the Babcock & Wilcox boiler owes its safety is
the construction made possible by the use of headers, by which the water
in each vertical row of tubes is separated from that in the adjacent
rows. This construction results in the very efficient circulation
produced through the breaking up of the steam and water in the front
headers, the effect of these headers in producing such a positive
circulation having been clearly demonstrated in Mr. Babcock's lecture.
The use of a number of sections, thus composed of headers and tubes, has
a distinct advantage over the use of a common chamber at the outlet ends
of the tubes. In the former case the circulation of water in one
vertical row of tubes cannot interfere with that in the other rows,
while in the latter construction there will be downward as well as
upward currents and such downward currents tend to neutralize any good
effect there might be through the diminution of the density of the water
column by the steam.

Further, the circulation results directly from the design of the boiler
and requires no assistance from "retarders", check valves and the like,
within the boiler. All such mechanical devices in the interior of a
boiler serve only to complicate the design and should not be used.

This positive and efficient circulation assures that all portions of the
pressure parts of the Babcock & Wilcox boiler will be at approximately
the same temperature and in this way strains resulting from unequal
temperatures are obviated.

Where the water throughout the boiler is at the temperature of the steam
contained, a condition to be secured only by proper circulation, danger
from internal pitting is minimized, or at least limited only to effects
of the water fed the boiler. Where the water in any portion of the
boiler is lower than the temperature of the steam corresponding to the
pressure carried, whether the fact that such lower temperatures exist as
a result of lack of circulation, or because of intentional design,
internal pitting or corrosion will almost invariably result.

Dr. Thurston has already been quoted to the effect that the admitted
safety of a water-tube boiler is the result of the division of its
contents into small portions. In boilers using a water-leg construction,
while the danger from explosion will be largely limited to the tubes,
there is the danger, however, that such legs may explode due to the
deterio