To the Editor of the SCIENTIFIC AMERICAN : I send a copy of a photograph of a novel bridge, which may interest your many readers. The bridge is one Douglas fir log, 4 feet in diameter and 54 feet between supports, and is used by prospectors to cross a stream on the western slope of the Cascade Mountains. The view shows the Washington State Road Commission crossing the structure. This photograph is one of a number of kodak views I took during the past summer while exploring a route for State wagon road across the Cascade Mountains. B. W. HUNTOON, Engineer State Road Commission. Fairhaven, Wash., October 22, 1895. Dalmatian Insect Flowers. According to De Boisse, the active principle of Pyrethrum cinerarifolium is a yellow resin soluble in ether, insoluble in water and very slightly soluble in alcohol, carbon bisulphide, or fatty bodies. It is readily decomposed by alkalies. To extract the active principle the author exhausts the flowering tops of the plant with ether. The principle thus extracted is described as being of the color and consistence of virgin wax, with an apple-like odor. From the fresh plants the active principle may also be extracted by macerating the finely-chopped flowering tops with half their weight of ether, vaselin oil, colza, or petroleum, according as the product is intended for medicinal or agricultural use. The mixture, after trituration, is allowed to macerate for seven or eight hours. It is then strongly pressed, the resulting liquid allowed to stand, and the supernatant yellowoily liquid separated from the watery portion, which is rejected. When prepared with vaselin oil, the oily solution is useful for human medicine, being a powerful insecticide. The solutions in colza or petroleum have a wide application in agriculture to destroy insect parasites, being applied direct to trees or shrubs. Emulsified with forty times their volume of soot water, they may be used for spraying the twigs and leaves.—Rev. de Scient. Natur.