Elliptic COMPASSES are used to draw ellipses or ovals. Compasses. They consist of a beam about a foot long, bearing three cursors, to one of which may be screwed points of any kind. To the bottom of the other two are rivetted two sliding dovetails, adjusted in grooves made in the cross branches of the beam. As the dovetails have a motion every way, by turning about the long branch, they go backwards and forwards along the cross; so that when the beam has gone half way about, one of these will have moved the whole length of one of the branches; and when the beam has got quite round, the same dovetail will have got back the whole length of the branch. The use of this compass is easy; by turning round the long branch, the ink, pencil, or other point, will draw the ellipse required.