This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1904 edition. Excerpt: ...of Caissons and Gates, considered as two distinct, though comprehensive, classes based on the foregoing definitions, may be broadly gauged as follows: --1. Gates with vertical axes need side recesses into which they may be swung when the entrance is to be opened for the passage of vessels. This necessitates a considerable and expensive addition to the length of the side walls, especially when the lock or entrance is of great width, as often obtains at the present day. Caissons do not occasion any increase in the length of the side walls, but, on the other hand, there must be reckoned the cost of a special chamber for sliding and rolling caissons. Ship caissons do not need a chamber, but, when out of use, they have to be berthed somewhere, and this leads to a certain amount of inconvenience in the appropriation of usef ul space. 2. Caissons are generally of stronger build and broader beam than gates, and they afford accommodation for the transmission of rail and road traffic across a waterway, thus discharging the functions of a bridge in addition to those peculiarly their own. 3. Thn first cost of a caisson is undoubtedly, in most cases, greater than that of a pair of gates, but if the cost of a swing bridge for vehicular traffic, which is a necessary adjunct in the case of gates, be also taken into consideration, the advantage will be found to lie with the caisson. This advantage is still further emphasised where a lock or passage is fitted with double gates to alternately impound or exclude water. A caisson can be constructed to act equally in both directions. 4. Caissons obviate the necessity for pointed sills and gate platforms of large area, but those of the ship type, fitting into grooves so as to be capable of acting in two..