within it. If moderately driven, the water may
struggle in against the issuing steam sufficiently to keep the surface
covered, but a slight degree of forcing will cause it to act like the
test tube in Fig. 3, and the more there are of them in a given boiler
the more spasmodic will be its working.

The experiment with our kettle (Fig. 2) gives the clue to the best means
of promoting circulation in ordinary shell boilers. Steenstrup or
"Martin" and "Galloway" water tubes placed in such boilers also assist
in directing the circulation therein, but it is almost impossible to
produce in shell boilers, by any means the circulation of all the water
in one continuous round, such as marks the well-constructed water-tube
boiler.

As I have before remarked, provision for a proper circulation of water
has been almost universally ignored in designing steam boilers,
sometimes to the great damage of the owner, but oftener to the jeopardy
of the lives of those who are employed to run them. The noted case of
the Montana and her sister ship, where some $300,000 was thrown away in
trying an experiment which a proper consideration of this subject would
have avoided, is a case in point; but who shall count the cost of life
and treasure not, perhaps, directly traceable to, but, nevertheless, due
entirely to such neglect in design and construction of the thousands of
boilers in which this necessary element has been ignored?

In the light of the performance of the exacting conditions of present
day power-plant practice, a review of this lecture and of the foregoing
list of requirements reveals the insight of the inventors of the Babcock
& Wilcox boiler into the fundamental principles of steam generator
design and construction.

Since the Babcock & Wilcox boiler became thoroughly established as a
durable and efficient steam generator, many types of water-tube boilers
have appeared on the market. Most of them, failing to meet enough of the
requirements of a perfect boiler, have fallen by the wayside, while a
few failing to meet all of the requirements, have only a limited field
of usefulness. None have been superior, and in the most cases the most
ardent admirers of other boilers have been satisfied in looking up to
the Babcock & Wilcox boiler as a standard and in claiming that the newer
boilers were "just as good."

Records of recent performances under the most severe conditions of
services on land and sea, show that the Babcock & Wilcox