at length. Neither the Federal Government nor any of the State Governments, however, concern themselves with the bridging of streams that are not navigable, unless it happen that suit against the builder or the proposed builder of the bridge be instituted in either a State or a Federal Court, when, of course, the law will be concerned.

The War Department nearly always confines its attention to a few salient features of any proposed crossing of a navigable stream, viz.; the span-lengths, the clear waterway for navigation, the angle of skew (if the crossing be not square), the position of the movable span or spans (if there be any), the clear headway above high water for both the movable and the fixed spans, the character and the dimensions of the draw protection, and the amount of obstruction to the flow of water caused by the piers—especially those parts thereof below low-water mark.

In spite of the fact that the War Department has certain rules for determining the span-lengths for crossing various navigable rivers, the said rules are more or less elastic; hence it will generally pay any consulting bridge engineer, or other engineer who intends to bridge navigable water, to con- sult first with. the local engineer of the Government who has charge of the district in which the proposed structure is located, and later, if necessary, with headquarters at Washington, in order to settle as to what the exact requirements of the Government will be. Often by stating one's case clearly and logically one can persuade the authorities to ease up on some regulation that appears to be unnecessarily strenuous or severe. For instance, the relation between the widths of clear openings required for swing spans and bascules or vertical-lift spans is a matter that has never been finally determined by the Department, each case as it arises being solved on its own merits.

Again, if the limiting length of span set by the Government does not exactly fit a crossing, one has to put in a shorter span at one end of the bridge, or to increase equally all the span-lengths, or else to obtain permission to decrease them equally. If the decrease be small, it is sometimes practicable to obtain the consent of the Department to the adoption of the shortened span-length.

In the case that the grade of a bridge is so low as to bring the clearance line too close to the elevation of high water to meet the Government requirements, it is sometimes possible to persuade the Department to permit an encroachment; but to do so would certainly be bad policy, for the limit set by the United States Engineers is adjusted about right to provide safety from passing drift.

In respect to the position of the movable span, the broad statement can be made that its mid-length should coincide with the deepest part of the channel, but there are occasional exceptions to the rule, notably when the channel is not permanent, or where it can advantageously be shifted by a little dyking. Permission to do such shifting and to locate the movable span accordingly would have to be obtained from the War Department.