ELLIPTIC COMPASSES, the name given to any machine for describing an ellipse. A simple method of forming the curve is to fas ten a pin in the paper at each of the two foci, and to attach to the piris the opposite ends of a thread whose length is equal to the major axis of the ellipse. Then, if a pencil move in such a way as to keep the thread always stretched, it will describe an ellipse: The ordinary machine 6orisiats of two bars of metal at right angles to One another, in each of which is a groove : two pins in a ruler, "of which one extremity carries a pencil, are Made to travel in the grooves, When the mo tion of the niter causes the pencil to describe an ellipse. The distances of the Pencil from the two pins are made equal to the semi-axes of the curve.
ELM. The elm-tree frequently grows to a very large size ; and the timber thus yielded has a scantling sufficient to adapt it for use in the keels of ships. The wood of the elm is of a brownish colour, hard, and fine-grained. Besides the keel, it is used for blocks, dead eyes, and other parts of a ship's fittings. It it frequently used for the naves of wheels ; and in London for coffins. It is used for the brine pipes or tubes in salt works. Many spe
cimens of elm are so beautifully grained and knotted, that this wood is largely used in the form of polished veneers.
As fuel and as tharctial the elm is not quite equal to the beech. The ashes are rich iu alkali. The leaves and young shoots are em ployed in France as food for cattle, and they are boiled as food for pigs: In some parts of Russia the leaves are used as tea. The outer bark is sometimes prepared into an astringent medicine; the inner bark is made into nets and cordage ; and both are made to yield a substance which serves as glue. In Norway the bark is kiln-dried and ground with corn as a material for bread.
Most of the above details refer to the com mon or English elm. The mountain or Scotch elm is likewise useful to the ship and boat builder, the pump and block maker, the cart wright, the the cabinet-maker, and other manufacturers. Floor-timbers of ships ; naves; poles, and shafts of carriages ; swingle trees for gun. carriages ; dyers' and printers' rollers—all are frequently made of Scotch elm.