The second or the recording lever has a normal excursion through 8 cm. on the recording surface, which is a very thin sheet of glass 8×8 cm. coated with a layer of smoke. As the recording lever is about 40 cm. in length, the curvature in the record is slight, and practically negligible in the middle portion of 4 cm. The dimensions given allow a magnification of ten thousand times. A far more compact apparatus is made with 15 cm. length of levers. This gives a magnification of a thousand times. AUTOMATIC RECORD OF THE RATE OF GROWTH. Another great difficulty in obtaining an accurate record of the curve of growth arises from the friction of contact of the bent tip of the writing lever against the recording surface. This I was able to overcome by an oscillating device by which the contact, instead of being continuous, was made intermittent. The smoked glass plate, G, is made to oscillate, to and fro, at regular intervals of time, say one second. The bent tip of the recording lever comes periodically in contact with the glass plate during its extreme forward oscillation. The record would thus consist of a series of dots, the distance between successive dots representing magnified growth during a second. The drawback in connection with the obtaining of record on the oscillating plate lies in the fact that if the plate approaches the recording point with anything like suddenness, then the stroke on the flexible lever causes an after-oscillation; the multiple dots, thus produced, spoil the record. In order to overcome this, a special contrivance is necessary, by which the speed of approach of the plate should be gradually reduced to zero at contact with the recording point. The rate of recession should, on the other hand, continuously increase from zero to maximum. The recording point will in this manner be gently pressed against the glass plate, marking the dot, and then gradually set free. It was only after strict observance of these conditions that the disturbing effect of after-vibration of the lever could be obviated. [Illustration: FIG. 57.--Eccentric for oscillation of plate K, crank; S, slide; P, holder for glass plate G. A, adjusting screws; L, recording lever. Clock releases string C for lateral movement of the plate. (From a photograph.)] This particular contrivance consists of an eccentric rod actuated by a rotating wheel. A cylindrical rod is supported eccentrically, so that semi-rotation of the eccentric causing a pull on the crank K (Fig. 57) pushes the plate carrier gradually forward. On the return movement of the eccentric, a light antagonistic spring makes the plate recede. The rate of the movement of the crank itself is further regulated by the device of the revolving wheel. This is released periodically by clockwork at intervals of one, two, five, ten, or fifteen seconds respectively, according to the requirements of the experiment. The complete apparatus is shown in figure 58.