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times smaller than the eye of a large louse. These exceeded all the former in celerity. I have often observed them to stand still as it were on a point, and then turn themselves about with that swiftness, as we see a top turn round, the circumference they made being no larger than that of a small grain of sand, and then extending themselves straight forward, and by and by lying in a bending posture.

I perceived in pure water, after some days, more of those animals, as also some that were somewhat larger. And I imagine, that many thousands of these little creatures do not equal an ordinary grain of sand in bulk; and comparing them with a cheese-mite, which may be seen to move with the naked

eye, I make the proportion of one of these small water-creatures to a cheese-mite, to be like that of a bee to a horse ; for, the circumference of one of these little animals in water is not so large as the thickness of a hair in a cheese-mite.

In another quantity of rain-water exposed for some days to the air, I observed some thousands of them in one drop of water, which were of the smallest sort that I had seen hitherto. And in some time after I observed, besides the animals already noted, a sort of creatures that were eight times as large, of almost a round figure; and as those very small animalcula swam gently among each other, moving as gnats do in the air, so did these larger ones move far more swiftly, tumbling round as it were, and then making a sudden downfall.

In the water of the river of Maese I saw very small creatures of different kinds and colours, and so small, that I could very hardly discern their figures; but the number of them was far less than of those found in rain-water. In the water of a very cold well in the autumn, I discovered a great number of living animals very small, that were exceedingly clear, and a little larger than the smallest I ever saw. In sea-water I observed, at first, a little blackish animal, looking as if it had been made

up of two globules. This creature had a peculiar motion, resembling the skipping of a flea on white paper, so that it might very well be called a water-flea; but it was far less than the eye of the water-filea.

Having put about one third of an ounce of whole pepper in water, and it having lain about three weeks in the water, to which I had twice added some snow-water, the other water being in great part exhaled, I discerned in it with great surprise an incredible number of little animals, of divers kinds, and among the rest, some that were three or four times as

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long as broad; but their whole thickness did not much exceed that of the hair of a louse. They had a very pretty motion, often tumbling about and sideways: and when the water was let to run off from them, they turned round like a top; at first their body changed into an oval, and afterwards, when the circular motion ceased, they returned to their former length. The second sort of creatures discovered in this water were of a perfect oval figure, and they had no less pleasing or nimble a motion than the former; and these were in far greater numbers. There was a third sort, which exceeded the two former in number, and these had tails like those I had formerly observed in rain-water. The fourth sort, which moved through the three former sorts, were incredibly small, so that I judged, that if 100 of them lay one by another, they would not equal the length of a grain of coarse sand; and according to this estimate, 1,000,000 of them could not equal the dimensions of a grain of such coarse sand. There was discovered a fifth sort, which had near the thickness of the former, but almost twice the length.

I thus order my division of the water, and the enumeration of the animalcula: I suppose that a drop of water equals a pea in bulk ; and I take a little quantity of water of a round figure, as large as a millet-grain; this I reckon to be the oto part of a pea: for when the axis of a millet-seed makes 1, that of a pea makes 41 : whence it follows, that the grain of a millet is at least the di part of a pea, according to the received rules of mathematicians. This small quantity of water I gather up into a very slender glass-pipe, dividing by this means that little water into 25 or 30 parts, of which I observe one part after another, and show the same to others.

Other spectators, as well as myself, judged that in z'o part of the water, equalling the bulk of a millet-seed, he saw more than 1000 living animals : but they wondered much more, when I said I saw it in two or three kinds of much smaller animals besides, which did not appear to them, because I saw them by another microscope, which I still reserve to myself alone. Hence it is manifest, that if in the so part of one millet-seed there are seen 1000, there may be seen 30,000 in one such whole seed, and consequently in a drop of water, which is 91 times larger than such a seed, there may

be 2,730,000. For, 41 x 41 x 4 = 91; and 91 × 30,000 : 2,730,000.

Otherwise, I compare the quantity of the water to the bulk of a grain of sand ; in which quantity of water I doubt not

seen

at all that I see more than 1000 animalcula. Now if the axis of a grain of sand be 1, the axis of a drop of water is at least 10, and consequently a drop is 1000 times larger than that sand, and therefore 1,000,000 living creatures in one drop of water. In which computation I rather lessen than heighten the number.

Last winter, when the severe cold had killed the little creatures, observing the water thawed by the warmth of the room in which it had stood for a whole day with a fire in it, I found after 24 hours were elapsed, and another time after 17 hours were passed, that some living animals appeared again in that water.

On the trembling of Consonant Strings. By Dr. WALLIS.

[1677.] SIR, — I have thought fit to notice a discovery that has been made here. Whereas it has been long since observed, that if a viol or lute string be touched with the bow or hand, another string on the same or another instrument not far from it, if an unison to it or an octave, or the like, will at the same time tremble of its own accord. The cause of it having been formerly discussed by many, I do not now enquire into. But add this to the former observation, that not the whole of that other string trembles, but the several parts severally, according as they are unisons to the whole, or the parts of that string which is so struck. For instance, supposing A C to be an upper octave to ay, and therefore an unison to each half of it, stopped at ß; now if, while ay

is
open,

AC be struck, the two halves of this other, that is, and By, will both tremble, but not the middle point at ß. Which will easily be observed, if a little bit of

A paper be lightly wrapped about

B the string ay, and removed successively from one end of the string to the other. In like manner, if A D be an upper twelfth to ad, and consequently an unison to its three parts equally divided in B, ya Now

A if, ad being open, A D be

A struck, its three parts, , By yê, will severally tremble, but not the points B, v;

which

A may

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as the former. In the same way, if A E be a double octave to the four quarters of this will tremble, when that is struck, but not the points B, 8. So if A G be a fifth to an, and consequently each half of that stopped in D, an unison to each third part of this stopped in ye, while that is struck, each part of this will tremble severally, but not the points y, e; and while this is struck, each of that will tremble, but not the point D. The like will hold in less concords, but the less remarkably as the number of divisions increases.

Of an unusual Meteor. By Dr. WALLIS. -- [1677.] An unusual meteor was seen Sept. 20th, 1676, about seven o'clock; which, though it seemed very low, was seen in most parts of England much at the same time, and much in the same manner. I hear of it from divers persons who saw it in Oxford, Northamptonshire, Gloucestershire, Worcestershire, Somersetshire, Hampshire, Kent, Essex, London, &c.

In the dusk of that evening, there appeared a sudden light, equal to that of noonday ; so that the smallest pin or straw might be seen lying on the ground. And above in the air was seen, at no great distance as was supposed, a long appearance as of fire ; like a long arm, with a great nob at the end of it, shooting along very swiftly; and at its disappearing seemed to break into small sparks or parcels of fire, like as rockets and such artificial fire-works in the air usually do. It was so surprising and of so short continuance, that it was scarcely seen by any who did not then happen to be abroad : its duration, by report, less than half a minute. It seems surprising that it was seen in most parts of England, and at or near the same time ; which argues, that either it was higher than the observers imagined, or else that it had a very swift motion.

On the Motion of Light. By M. ROMER. -- [1677.] Philosophers have been endeavouring for many years to decide, by some experiment, whether the action of light be conveyed in an instant to distant places, or whether it requires time. M. Romer of the Royal Academy of Sciences has devised a way for this purpose, taken from the observations of the first satellite of Jupiter, by which he demonstrates, that for the distance of about 3000 leagues, which is nearly equal to the diameter of the earth, light needs not one second of time.

The necessity of this new equation of the retardment of light is established by all the observations that have been made in the Royal Academy, and in the Observatory for the space of eight years; and it has been lately confirmed by the emersion of the first satellite observed at Paris, the 9th of November last, at 5 o'clock, 35m 458 at night, 10 minutes later than it was to be expected, by deducing it from those that had been observed in the month of August, when the earth was much nearer to Jupiter : which M. Romer had predicted to the said Academy from the beginning of September.

Mr. LEUWENHOEK concerning the Carneous Fibres of a

Muscle, and the Cortical and Medullary Part of the Brain. - [1667.]

I took the flesh of a cow; which I cut asunder with a sharp knife, and using a microscope I severed before my eyes the membrane from it; by which I plainly saw that fine membrane or film, in which these carneous fibres lie interwoven. Observing these membranes more narrowly, I saw that they wholly and only consist of small threads running through each other ; of which some appeared to be 10, 20, and even 50 times thinner than a hair. Having taken off these membranes from the carneous filaments, I saw very clearly these carneous threads, which in this piece of flesh were as thick as a hair on the hand. Where they lay rather thick on each other, they appeared red; but the thinner they were spread the clearer they showed.

I have used several methods of viewing the particles of these carneous filaments, and have always found that they are composed of globular parts. I have also divided before my eye, into many small parts, very small pieces of these carneous filaments, which pieces were several times smaller than a grain of sand ; and I have observed, besides, that, when the flesh is fresh and moist, and its globules are pressed or rubbed, they dissolve and run together, in appearance like an oily or thick waterish matter; which globules appeared so small, that 1,000,000 of them would not make one grain of gravel sand. The general figure of these globules were roundish, but a little compressed, like a multitude of very small blown bladders, lying on a heap.

I have examined, also, that membrane of the brain, which is called pia mater, and found that it is permeated by very many small veins, besides those which with the naked eye we see on the brain, especially having first separated the thin mem

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