any type of deck that can be used on a fixed span, which is not the case for a bascule. That type of movable span necessitates a timber deck with its consequent fire-risk.

Second. Great wind pressure during operation has no appreciable effect on a vertical lift, while it may cause serious delay to a bascule, or even, under extreme conditions, prevent its operation altogether.

Third. The vertical lift does not have to rise so high for low-masted passing craft as does the bascule; and thus it saves a considerable amount of time and power.

Fourth. In railroad bridges when the moving span is down, it acts just like any fixed span, as far as operation under traffic is concerned, which cannot be said for either the swing or the double-leaf bascule; or; in other words, for railroad traffic the vertical lift is the most rigid of the three types, excepting only in the case of the single-leaf bascule, which is usually quite rigid.

Fifth. In case of a shifting channel, it is feasible to make a number of the spans alike and to arrange, for any time in the future and at comparatively moderate expense, to have the towers and machinery taken down, transferred, and re-erected, so as to lift any one of the said like spans. This could not by any possibility be done in the ease of any other type of movable structure.

Sixth. The vertical lift, when its towers do not rest on flanking spans, lends itself readily to a future raising or lowering of the grade line in a way that no other type of movable span can possibly do; for all that is necessary is to change the elevation of the bearings of the lift span. If a change of grade be anticipated when the plans are being prepared, provision should be made therefor by increasing adequately the heights of the towers; but if at any time the grade on a vertical-lift bridge of the type mentioned, for which no such preparation has been made, has to be raised to such an extent that there will be interference because of the counterweights, reaching the new decks of the approaches in the towers, the result desired could be accomplished by arranging for a small portion of the said approaches to move either laterally or vertically out of the way of the counterweights, whenever a very-tall-masted vessel has to pass. For any other vessel, however, these moving approaches would not have to be utilized; consequently, they would seldom need to be operated.

Seventh. The vertical lift accommodates itself to a skew crossing far better than does the bascule, as in the latter the tail has to be squared, while in the former both the span and the towers may be skewed, thus reducing the clear waterway (and consequently the length of moving span) to a minimum.

Eighth. By spanning the opening between tops of towers in a vertical-lift bridge, electric-wires, water-pipes, and gas-pipes can be carried across; but the  accomplishment  of  this  in  the  case of a bascule or a swing would