Hollow Steel Spars

Mechanical skill of no ordinary character is reqvrired to produce the hollow steel boom, the spar which has uow become so noted in marine architecture, advautage being gained, in exigencies, by begirming in the center and rivetiug the plates toward both ends. In the most recent instanceof this construction there were four lines of angle irou bracea at equal distances from each other and running the whole length. of the boom, giving it a good bracing, the face to the angles being slightly curved to take the concave shape of the interior of the boom, these angles consisting of sections measuring on au average some 15 feet, with a lap made at each joint 1 inches in length and bolted with steel. Theee laps are irregular, in order that two joints or more may not be opposite each other and thus cause weakness.