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and the piles are strong and driven with heavyrams till they will sink no further, intervals ofat least 30 feet may be used; and any defi-ciency in the length and strength of the mate-rials* forthcoming for beams, may be madegood by the different methods of scarfing andtrussing treated of in the following article.

On Wooden Bridges formed of Trusses, and otherprinciples of Carpentry.

The construction of wooden bridges to spanimpediments too wide for the simple applica-tion of the timber at command, is an importantbranch of our subject.

Beams of considerable length may be madeto support great weights by means of a certainapplication of frame work called, in carpentry,a truss.

This subject is closely connected with theconstruction of the roofs of large buildings, andthe centres used in building stone arches: itconsists of frames of timber, in which the beams

* The reader, or practitioner, who desires the fullest andbest information on this subject, is referred to Mr. Barlow’sexcellent Treatise on the Strength of Materials . The Indianpractitioner will find, at pages 14 and 15, Appendix , tablescontaining the experimental strength of woods, the growth ofIndia , reduced, for practical purposes, to the terms necessaryto find the value a, or strength, to be applied in practice, fromthe formula 1 given at page 11.