Show hollow steel sled spars mechanical skill of no ordinary character is required to produce the hollow bollow steel boom the spar bich has bas now become so noted in marine majino architecture advantage being gained in exigencies by beginning in the center and riveting the plates toward both ends in the most recent instance of this construction there were four lines of angle iron braces 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 thew these angles consisting of sections measuring on an average some 15 feet with a lap nade made at each joint 1 2 1 inches in length and bolted with steel these laps are am irregular iu in order that two joints or more may not bo be opposite each other and thus causo cause weakness |