This Needle or Tracer is of finely polished steel, brought to a very fine point at its lower end, and so arranged as to permit of very accurate and delicate adjustment sideways by means of two screws HH shown on the drawing.

Attached to the Needle is the Tracer Rest E which is adjustable in height and which forms the point of support instead of the needle itself. By proper adjustment as to height it allows of the point of the Tracer being brought very near to the surface of the drawing paper, hovering over it but not touching it. The Rest also acts as a handle and guide by means of which the Tracer can be accurately guided along any desired path or along the outline of any figure, and greatly facilitates the accurate tracing of any bounding line. In the most improved forms of Planimeters the form of Rest is modified from that just described, and is shown its improved form in Fig. 2 of Plate IX. One important improvement consists in enclosing the Tracer Needle in a spiral spring in such a manner that while during the ordinary operations of tracing the needle does not touch the paper, by pressing the top of the needle with the finger the needle is forced down so that its point enters the paper and makes a fine buy very distinct hole which remains as a permanent mark at the starting point or at any other point it may be desirable to preserve. On removing the pressure of the finger the needle at once resumes its adjusted position.

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