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152 variation of growth. It will be seen that if we succeeded in enhancing magnification from twenty to ten thousand times, the necessary period for experiment would be reduced from four hours to thirty seconds. The importance of secur- ing a magnification of this order is sufficiently obvious.

The problem of high magnification was first solved by my Optical Lever. The tip of the growing organ was attached to the short arm of a lever, the axis of which carried a small mirror ; in this way it was possible to obtain a magnification of a thousand times. The magnified movement of growth was followed with a pen on a revolving drum. The record laboured under the disadvantage of not being automatic. This defect was overcome by the use of the photographic method which however entailed the inconvenience and discomfort of a dark room.

I have, for the past six years, been working with a different method, which has now been brought to a great state .of perfection. The problem to be solved was the devising of a direct method of high magnification and the automatic record of the magnified rate of growth.

The magnification in my Crescograph is obtained by a compound system of two levers. The growing plant is attached to the short arm of a lever, the long arm of which is attached to the short arm of the second lever. If the magnification by the first lever be m, and that by the second, w, the resulting magnification would be mn.

The practical difficulties met with in carrying out this idea are very numerous. It will be understood that just as the imperceptible movement is highly magnified by the