HIGH AND LOW BOILEKS.

31

same. The smoke box is in a line with theextension of the combustion chamber. Withthis arrangement of details a short tube isimperative, while the requisite number makesgood the surface required.

The next example consists of the fire boxesbeing situated at each end of the shell, withseparate combustion chambers and waterspaces, thus forming the entire length. Thetubes are secured at the side of each fire box,having a return action, and height being°f importance in the present case, the smokefrom one end of the boiler—fore or aft—returns through a separate compartment orbox extending from end to end of the boiler ;f°r, by this arrangement, the products ofc °mbustion can escape through one funnel.

In order to obviate the necessity of thea dditional smoke box—as in the last example‘—the following arrangement has beendevised : the fire boxes are centrally situateda t each end of the shell; the combustionchambers are entirely separate, extending

partially across the shell; the tubes are atboth sides of the fire boxes. At each end ofthe boiler—at the outer sides of the fire boxes•—are second combustion chambers; a secondseries of tubes from these connect to a smokeb.ox, centrally secured in the length andbreadth of the shell. By this it will beunderstood a double return tubular action isattained, and it may be added in passing, thatthe entire length and breadth of the shell inquestion will not be increased in proportion tothose of the preceding examples.

In all devices for arrangement of boilers, asimilarity—or, rather, an equality—of flame-action should be maintained, which in the lastexample is certain. The types of boilers nowunder notice are worthy of more attentionthan has been the universal practice. Thismay be said to be due to the isolated require-ment of the case; but should a future im-provement, for national purposes, be desired,the British Marine Engineer will as beforenow be equal to the task.

END OF PREFATORIAL REMARKS.