74 All About Engines
plates behind each bank of tubes. The circulation
of the water is a little difficult to follow ; but the feed
enters the back top drum, passes to the back lower
drum, whence it passes to the front lower drum.
Fig. 38.—Interior of a Stirling boiler
Steam is generated in the first three banks of tubes,
and collects in the middle top drum. Another variety
differs mainly in having straight tubes. Both are
efficient, but take up a good deal of space.
The next type is that made by Messrs. Babcock
and Wilcox, Ltd., who have works in England, and