Dry firing refers to releasing the bowstring without a nocked arrow. The bowstring truss bridge was patented in 1841 by Squire Whipple. Crossbows incorporate a type of latch to hold the drawn bowstring prior to firing. The bowstring and arrow are held with three fingers, or with a mechanical arrow release. The knot can be adjusted to lengthen or shorten the bowstring. The bow is made of bamboo or wood, while the bowstring is made of rattan. Longus also acts like a bowstring that braces the transverse arch of the foot. Compound bows have a mechanical system of pulley cams over which the bowstring is wound. The barges hit Pier 17 bringing down two bowstring girders. The 160-foot bowstring arch design spanned the Neosho River east of what is now Chanute. Returning the bowstring to its ready-to-use position is called "stringing" the bow. The bowstring was called jya, and was strung only when needed. This keeps the forearm out of the way of the bowstring. The needle is placed vertically on the bowstring. The bridge is of steel bowstring construction, with a span.