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tenons, fig. 22, which are secured in correspond-ing mortises, fig. 21, by wedges, fig. 23.

The inside width of the frames is four feet.The floor is carried in separate pieces, I I, fig. 24.

A bridge for infantry may be readily formedacross a ditch not more than 26 feet wide, byone of these frames, fig. 20, which has beenproved to bear twenty-three men. One cart,fig. 25, drawn by two horses, carries two framesand their appertenances.

Two frames laid close to each other, form abridge sufficient for any nature of field artillery,over a ditch not above 26 feet wide.

A bridge for infantry may be made over acanal or river not more than 50 feet wide, and 11feet deep, by the following application of twoframes. Unload the carriage: place the backpart towards the river, and the shafts in theposition 13 C, fig. 1, plate 8. Shift the beam Ato such a position upwards on the shafts, as thedepth of the river may require. Set up, andcomplete the frames; lay the end of one of themon the beam A, and lash it to the first transomE, fig. 20, plate 7. Confine the shafts in thisposition by the rope C I), which fasten to thefurther end of the frame, and push the carriageinto the water, till the end of the frame is withinfour feet of the bank E, fig. 2; then let go the