502

HISTORY OF ENGINEERING.

Book I.

As the lozenges diminish in size, the iron-work of which they are formed is also relativelylessened in dimension; the lower points of the lozenges rest upon the centre,.the upper

Fig. 500.

support the bridge road. The vertical sides which compose the ribs are united with screwbolts, passing through the rims raised on the outside, which are occasionally increased in

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Fig. 501.

PLAN SHOWING STAIRS.