This section is from the book "The Home Cyclopedia Of General Information", by Charles Morris. Also available from Amazon: Home Cyclopedia of Necessary Knowledge.
[Fr.] An apparatus used in laying the foundation of bridges under water. One form is an inverted water-tight hollow box with iron-bound edges, in the bottom of which some masonry has been constructed. The weight of the masonry forces the caisson into the sand and mud at the bottom, and air, under pressure, is then forced in, driving out the water and allowing the workmen to enter through the air tight locks.
 
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