An instrument for measuring and transferring the angle formed by two surfaces; it consists merely of two straight legs, turning upon a common centre, and is used by the two limbs coinciding with the surfaces where an angle is to be ascertained. The annexed engraving represents an instrument by which curved surfaces may be gauged, or the curve transferred to any kind of work, or to paper, a and b Fig. 1, are two rulers connected together by a en cular joint; c is an arch of brass fixed to b, and sliding through a mortise or slit in a, to which it is fastened at pleasure, at any required angle, by means of the screw in a pressing upon it. The rule a has six or more square mortises made through it, (shewn in section in the drawing,) in which are placed as many nuts moving on pivots; each of these nuts is tapped to receive a long screw (as at f,) working within them; and each of the long screws is fixed at one end to a flexible steel blade, e e, by means of a kind of swivel joint which admits of the screw turning round in it without advancing, and allows it to press either direct or aslant.

Consequently, when the opposite ends of the screws are turned by the thumb and forefinger, the steel blade is pressed out so as to adapt itself to any given curve; and being thereby fixed in the same position, the curved line can be transferred therefrom to any kind of work, or on to paper. Fig. 2 shews a contrivance for drawing the radii of wheels with great expedition; it is formed of a slip of thin brass, and the central hole must be in the line o o; if now a needle point passing through the hole be inserted in the centre of the circle representing the wheel, the radii may be drawn with great facility and exactness along either of the lines o o, to the different points or degrees previously marked upon the circumference.

Bevil 164

Fig. 2.

Bevil 165