'It is wonderful,' he says, 'to see the rising of the sap in Trees. All will bleed more or less when they are tapped by boring a hole through the Bark, some very considerably, as Birch, which will afford as much liquor every day almost as the milke of a cow; in a Vine when a bough is cut off it will if not stopped bleed to death. Now by what mechanisme is water raised to such a height, as in Palmitos to 120 foot high? A skillfull Engineer cannot effect this without great force and a complicated engine, which Nature doth without sensible motion; it steals up as freely as the water descends: the reason of this is obscure as yett to naturalists.' After some discussion of various theories, he proceeds to show by the help of the little drawing, 'that the onely Vicissitudes of heat and cold in ye aire is sufficient to raise the sap to the height of the loftiest trees.' Then follows the proof of this by mechanics refuting the notion of 'a secret motion in nature contrary to that of the gravity, by which plants aspire upwards. 'But though I have shown how the sap may be mechanically raised from the Root to the top of the loftiest trees, yett how it comes to be varyed according to the particular nature of the Tree by a Fermentation in the Root; how the Raine water entering the Root acquires a spirit that keeps it from freezing, but also gives it such distinguishing tastes and qualities is beyond mechanical Philosophy to describe and may require a great collection of Phenomena with a large history of plants to shew how they expand the leaves and produce the Seed and Fruit from the same Raine water so wonderfully diversified and continued since the first Creation.' Another paper of the same date was written 'On the surface of the terrestrial Globe,' but this does not appear to have been preserved. Many of Sir Christopher's writing's and many also of his inventions were lost by Mr. Oldenburg, the Royal Society's secretary, of whom Wren frequently complained that he not only neglected to enter them on the Society's Register, but conveyed them to France and Germany, where they appeared, attributed as inventions to those who had stolen them. One cannot but admire the versatility of mind which enabled Wren, in the midst of great architectural works, and endless business details, to write papers such as these, and to digest and decide upon Flamsteed's long letters on the Earth's motion, his quarrels with Mr. Halley, and his measurement of the height of the Welsh hills. [_LONDON AS IT WAS._]