with just the same head, but about five feet long; towards the head in this 60 joints scarcely made an inch, but at the tail about three equalled that space; and the joints here were about a quarter of an inch broad; and in the sides of the joints in this, I plainly perceived those orifices I at present call the mouths.

Letter from Mr. ANTHONY LEUWENHOEK, of Delft, concerning the Appearances of several Woods, and their Vessels. [1683.]

I SEND you here some observations on wood. BCD (fig. 1.) is a part of the circumference of an oak or ash tree, &c. being of 18 years' growth, and therefore having 18 rings, one for each year; that which

is made the last

year being al

ways the greatest, though not always proportionably great, but according as the year is more or less fruitful.

Fig.1.

B

The pieces described in the following figures are such as E in the 15th ring, and sometimes not so large; yet from such a part I doubt not but the constitution of the whole tree may sufficiently be understood.

When a tree is sawed across, and afterwards planed very smooth, we see lines, as it were, drawn from the centre A, and reaching to the circumference B; these are vessels which carry the sap to the bark; as by the adjoined figures will appear.

In fig. 2. ABCD shows a piece of oak, which observed in a microscope was thus drawn from a piece of wood as large as Fig.2.

H. FF are the separations of the growth of one year. For when the growth stops, the wood becomes firm and thick; and is supplied with many small vessels, such as are hardly to be distinguished, and therefore appear as brown rays or streaks. Between the said FF, FF, is comprehended that thickness of wood which has been added to the circumference of a tree by a year's growth. The wood has five sorts of vessels, viz. Three sorts going upwards, and two lying horizontally. EEE denote large ascending vessels made every year in the wood in the spring, when it begins to grow.

All these ascending vessels in the aforesaid piece of wood, which is about of a square inch, are I guess about 20,000. Hence in an oak-tree of four feet diameter are 3200 millions of ascending vessels, and in one of one foot there are 200 millions of vessels. If we suppose 10 of these great and small vessels in a day to carry up one drop of water, and that 100 of these drops make one cubic inch, there will be 200,000 cubic inches.

These forementioned uprising vessels empty constantly their sap into an incredible number of vessels, which lie horizontally in the body of the tree, to cause a continual growth in thickness. Fig. 2., G G G, are a sort of vessels which run horizontal, beginning from the pith of the tree, but afterwards in great numbers taking their rise from the ascending vessels.

Fig. 3. is a little piece of black Mauritius ebony wood, and this little piece of wood, wherein are shown about 1100 rising vessels, is no larger than an ordinary grain of sand..

Fig. 4. is a piece of palmwood; and though I examined a great deal of it, I could find

Fig. 3.

little difference in the several parts, and therefore I have

Fig. 4.

here contented myself with describing a smaller portion. It consists of two sorts of ascending vessels, viz. great vessels, and smaller ones lying among the larger.

ABCDEF (fig.5.) is a very small piece of straw cut across, in which the part of the circumference AF may be discerned how great it is. ABEF is the rind of the straw, which to outward appearance is smooth

and shining, though for the most part it is made of extremely small vessels, and of some greater; which I have represented

B

F

as near as possible. GG GG are the vessels of which the innermost parts of the straw are made; these vessels are four, five, and six sided, according as they come to fit themselves. HHH are other vessels which run in between the forementioned ones, and are beset round with small vessels. In these vessels I have seen the sap sink down suddenly at the time of the growing of the straw, when at the same time I saw the sap rise up in the vessels GG, which sap was made mostly of globules; and when the globules came to pass the valves, where the vessels were narrowest, these globules then changed into the form of cones, till they obtained a larger room, and then they retook their former globular shape.

A Conjecture on under Currents at the Straits' Mouth and other Places. By THOMAS SMITH, D.D. — [1684.]

AT the Straits, there is a vast draught of water poured continually out of the Atlantic into the Mediterranean; the mouth or entrance of which between Cape Spartel or Sprat, as the seamen call it, and Cape Trafalgar, may be near seven leagues wide, the current setting strong into it, and not losing its force till it runs as far as Malaga, which is about 20 leagues within the Straits. By the benefit of this current, though the wind be contrary, if it does not overblow, ships easily turn into the Gut, as they term the narrow passage, which is about 20 miles in length. At the end of which are two towns, Gibraltar on the coast of Spain, which gives denomination to the strait, and Ceuta on the Barbary coast; at which places Hercules is supposed to have set up his pillars. What becomes of this great quantity of water poured in this way, and of that which runs from the Euxine into the Bosphorus and Propontis, and carried at last through the Hellespont into the Egean or Archipelago, is a curious speculation, and

has exercised the ingenuity of philosophers and navigators. For there is no sensible rising of the water all along the Barbary coast, even down to Alexandria, the land beyond Tripoli, and that of Egypt lying very low, and easily to be overflowed. They observe, indeed, that the water rises three feet or three feet and a half in the Gulf of Venice, and as much, or very near as much, all along the river of Genoa, as far as the river Arno; but this rather adds to the wonder.

I here omit to speak at large of the several hypotheses which have been invented to solve this difficulty; such as subterraneous vents, cavities, and indraughts, exhalations by the sun-beams, the running out of the water on the African side, as if there were a kind of circular motion of the water. My conjecture is, that there is an under-current, by which as great a quantity of water is carried out as comes flowing in. To confirm which, besides what might be said about the difference of tides in the offing, and at the shore in the Downs, which necessarily supposes an under-current, I shall present you with an instance of the like nature in the Baltic sound, as I received it from an able seaman, who was at the making of the trial. He told me, that being there in one of the king's frigates, they went with their pinnace into the mid stream, and were carried violently by the current; that soon after they sunk a bucket with a large cannon ball, to a certain depth of water, which gave check to the boat's motion, and sinking it still lower and lower, the boat was driven ahead to windward against the upper current: the current aloft, as he added, not being four or five fathom deep, and that the lower the bucket was let fall, they found the under current the stronger.

Of the Pores in the Skin of the Hands and Feet. By NEH. GREW, M.D.-[1684.]

THE pores in the hands and feet are very remarkable ; both in respect of their position and their amplitude. For if any one will but take the pains, with an indifferent glass, to survey the palm of his hand very well washed with a ball, he may perceive innumerable little ridges, of equal size and distance, and every where running parallel to each other. And especially on the ends and first joints of the fingers and thumb, on the top of the ball, and near the root of the thumb a little above the wrist. In all which places, they are very regularly disposed into spherical triangles and ellipses. On these ridges stand the pores, all in even rows, and of such a

magnitude, as to be visible to a good eye, without a glass. But being viewed with one, every pore looks like a little fountain, and the sweat may be seen to stand therein, as clear as rock-water, and often as it is wiped off, to spring up within them again.

What nature intends in the position of these ridges, is, that they may the better suit with the use and motion of the hand those of the lower side of every triangle, to the bending in or clutching of the fingers; and those of the other two sides, and of the ellipses, to the pressure of the hand or fingers' ends against any body, requiring them to yield to the right and left. On these ridges the pores are very providently placed, and not in the furrows which lie between them; that so their structure might be the stronger, and less liable to be depraved by compression; whereby only the furrows are dilated or contracted, the ridges constantly maintaining themselves, and so the pores unaltered. For the same reason, the pores are also very large, that they may still be the better preserved, though the skin be ever so much compressed and condensed, by the constant use and labour of the hand. So likewise those of the feet, notwithstanding the compression of the skin by the weight of the whole body.

Letter from Mr. ANTHONY LEUWENHOEK, about Animals in the Scurf of the Teeth, the Substance called Worms in the Nose, and the Cuticula consisting of Scales.[1684.]

THOUGH my teeth are kept usually very clean, yet when I view them in a magnifying glass, I find growing between them a little white matter, as thick as wetted flour: in this substance, though I could not perceive any motion, I judged there might probably be living creatures. I therefore took some of this flour, and mixed it either with pure rain-water wherein were no animals, or else with some of my spittle, having no animals nor air-bubbles to cause a motion in it; and then to my great surprize perceived that the aforesaid matter contained very many small living animals, which moved themselves very strangely. The largest sort were not numerous, but their motion strong and nimble, darting themselves through the water or spittle, as a jack or pike does through the water. The second sort spun about like a top, and were more in number than the first. In the third sort I could not well distinguish the figure, for sometimes it seemed to be an oval, and other times a circle: these were exceedingly small, and so swift, that I can compare them to nothing better than