Page:Life Movements in Plants.djvu/184

154 be greatly reduced ; or a constant tension may be exerted by means of a weight T (Fig. 56). In my later type

Fig. 56. — Compound lever. P, plant attached to short arm of lever L ; T, weight exerting tension; C, connecting link; L,' second lever with bent tip for record ; B, B, balancing counterpoise. Fork F, carries at its side two conical agate cups, on which lever rests by two pin-points. (From a photograph.)

of the apparatus the plant connection is made to the right, instead of the left side of the first fulcrum. This gives certain practical advantages. The second lever is then made practically to balance the first, only a very slight weight being necessary for exact counterpoise. The reduction of total weight thus secured reduces materially the friction at the fulcrum with great enhancement of efficiency of the apparatus.

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 8x8 cm, coated with a layer of smoke. As the recording lever is about 40 cm. in length,