_Calibration._--The calibration of the instrument is obtained in two different ways. The rate of subsidence of the plant-holder, by which the balance is obtained, is strictly proportional to the rate of rotation of the vertical spindle and the attached train of clock-wheels. A striker is attached to one of the wheels, and a bell is struck at each complete revolution. The clockwork is adjusted at a medium speed, the bell striking 35 times in a minute. A microscope micrometer is focussed on a mark made on the plant-holder, and the amount of subsidence of the mark determined after one minute; this was found to be 0·0525 mm. As this fall occurred after 35 strokes of the bell the subsidence per stroke was 0·0015 mm. _Determination of the absolute rate of growth._--If growth be found balanced at N strokes of bell per minute, the rate of subsidence per second = N × ·0015/60 mm. per second = N × ·000025 mm. per second = N × ·025 µ per second = N × 10^{-5} inch per second. _Example._--The growth of a specimen of _Zea Mays_ was found balanced when the number of strokes of the bell was 20 times in a minute. Absolute rate of growth = 20 × ·025 µ = 0·5 µ per second or = 20 × 10^{-5} inch " or = 1/50,000 " " If we take the wave length of sodium light [Greek: lambda] as our standard, the growth in length per second is equal to [Greek: lambda]. This will give us some idea of the sensitiveness of the Crescograph employed in recording the movement of growth. GROWTH-SCALE. The Balanced Crescograph enables us not merely to determine the absolute rate of growth, but the slightest fluctuation in that rate. _Indicator Scale._--All necessity of calculation is obviated by the scale provided with the apparatus. The speed of clockwork which brings about the balance of growth is determined by the position of the adjusting screw S, the gradual lowering of which produces a continuous diminution of speed. A particular position of the screw therefore indicates a definite rate of subsidence for balancing growth. By a simple mechanism the up or down movement of the screw causes rotation of an index pivoted at the centre of a circular scale. Each division of the scale is calibrated by counting the corresponding number of strokes of the bell per minute at different positions of the adjusting screw. The scale is calibrated in this manner to indicate different rates of growth from 0·2 µ to 1·2 µ per second. The determination of the rate of growth now becomes extremely simple. Few turns of the screw bring about the balance of growth and the resulting position of the index against the circular scale automatically indicates the absolute rate. The procedure is even simpler and more expeditious than the determination of the weight of a substance by means of a balance. SENSITIVENESS OF THE CRESCOGRAPHIC BALANCE.