CYLINDRICAL RETURN TUBULAR ARRANGEMENT.

in this example to attain the same by cross bars,rather than vertical stays connected to the shell.

Now, it may be considered by some authori-ties, that any connections with the shell as asupport for any of the parts or surfaces of theinternal portions, is a truthful illustration ofthe proverb that “ unity is strength.” Withboilers, however, the rule should be—inde-pendent strength due to the form of theinternal structure without connection withthe shell if possible.

The back of the combustion chamber is the

137

attainable with a proportionate thickness ofplate, independently of staying. Now, withthe flat shell, this rule is far from absolute;because if in that case an increase of pressuremust be resisted, it can only be maintained bysecuring the stays at a pitch, proportionatelyto the surfaces exposed to the pressure of thesteam—the requisite increase for the thicknessof the plates, laps of plates, and riveting, beingof course also duly considered.

Having thus explained further the gainthere is with cylindrical boilers, a considera-

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RETURN TUBULAR CYLINDRICAL MARINE LOW BOILER.

only internal surface, with the position ofthe details illustrated, that requires stays forintermediate resistance to the common pressure.These stays, therefore, are not only adequatefor that purpose, but they also form a supportfor the end of the tube or fire box.

This simplicity of construction, combiningstrength, with the form of shell in question, isobviously not produced with any other ar-rangement of previous explanation. Also, itis certain that, with the tubular form of shelland fire box, an increase of strength is directly

tion of the objections presented with thesame will be of value. The principal objec-tion, as previously stated, is the waste of thespaces between the shells, for marine boilers,which of course is more condemnable with anumber of boilers than when one or two areused; because without an intermediate space,available for coal bunkers, the waste of cubicalcapacity is increased, but on the contrarywhen the shells are arranged in continuouscontact with each other. Now, to furtherexemplify, presume a boiler is required of 100

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