The instrument we are about to describe is an improvement on the hatchet planimeter and is due to Prof. Goodman, of Leeds. One form of the instrument is intended for the measurement of areas of surfaces, and the other form for the measurement of the mean height of a figure such as an indicator diagram. London Engineering, to which we are indebted for the cuts and copy, describes the instruments as follows: The method of using the two instruments is practically the same, but for the present we shall confine our remarks to the instrument for measuring areas. In order to familiarize oneself with the peculiar action of the instrument, it will be well to get a large sheet of paper on a drawing board or a large blotting pad, and holding the instrument vertical to the paper, grasp the tracing leg very lightly indeed between the forefinger and thumb of the right hand, with the hatchet toward the left hand, as shown in Fig. 1. Then by moving the tracing point round and round an imaginary figure and allowing the hatchet to go where it pleases, it will be seen that the hatchet moves to and fro along zigzag lines, and travels sideways--the side travel being nearly proportional to the area of the figure described by the tracing point. If the tracing point be too tightly grasped, the hatchet will not move freely, and, will have a side slip. When this occurs the side travel of the hatchet ceases to be proportional to the area traced out. A loose weight is hung on the hatchet to prevent this side slip, but as soon as a little skill is attained in the use of the instrument, this weight may be dispensed with. [Illustration: GOODMAN'S HATCHET PLANIMETER.]