by and by the spider leaped into the air, and the thread mounted her up swiftly.

After this first discovery, I made the like observation in almost all the sorts of spiders I had before distinguished; and I found the air filled with young and old, sailing on their threads, and undoubtedly seizing gnats and other insects in their passage; there being often as manifest signs of slaughter, as legs, wings of flies, &c. on these threads as in their webs below. Many of these threads that came down out of the air were not single, but snarled and had complicated woolly locks, now more now less; on these I did not always find spiders, though many times I had found two or three upon one of them; whereas when they first flew up, the thread was always single, or but little tangled, or thicker in one place than another. I observed them get to the top of a stalk or bough, or some such thing, where they exercise this darting of threads into the air, and if they had not a mind to sail, they either swiftly drew it up again, winding it up with their fore feet over their head into a lock, or break it off short, and let the air carry it away. This they will do many times together, and you may see those that have chains of these locks or snarled thread before them, and not yet taken flight.

Again, I found, that after the first flight, all the time of their sailing they made locks, still darting forth fresh supplies of thread to sport and sail by. It is further to be noted, that these complicated threads are much more tender than our house-webs.

In winter, about Christmas, I have observed them busied in darting; but few of them sail then, and therefore but single threads only are to be seen; and besides, the young ones only of last autumn's hatch are then employed, and it is more than probable that the great ropes of autumn are made only by the large ones, and upon long passages and summer weather, when great numbers of prey may invite them to stay longer up in the air.

Concerning the Eruptions of Mount Etna.[1669.]

THE eruption took place on the 11th of March, 1669, about two hours before night, on the south-east side or skirt of the mountain, about 20 miles beneath the Old Mouth; and 10 miles from Catania. At first it was reported to advance three miles in 24 hours; but April 5. it scarce moved after the rate of a furlong a day; and at this degree of

progress it continued for 15 or 20 days after, passing under the walls of Catania a good way into the sea; but about the latter end of this month (April) and the beginning of May, it bent all its force against that city; and passed in divers places over the walls; but its chief fury fell on the convent of the Benedictines, having large gardens and other ground between them and the wall: which when it had filled up, fell with all its force on the convent.

it

The matter which thus ran was nothing else but divers kinds of metals and minerals, rendered liquid by the fierceness of the fire in the bowels of the earth, boiling up and gushing forth like the water at the head of some great river; and having run in a full body for a good stone's cast or more, the extremities thereof began to crust and curdle, forming when cold those hard porous stones which the people call sciarri, having the nearest resemblance to huge cakes of sea-coal, full of fire. These came rolling and tumbling over one another, and where they met with a bank, would fill up and swell over, by their weight bearing down any common building, and burning whatever was combustible. The chief motion of this matter was forward, but it also dilated itself, as a flood of water would do on even ground.

About two or three o'clock at night we mounted a high tower in Catania, whence we had a full view of the mouth; which was a terrible sight. Next morning we would have gone up to the mouth itself, but durst not come nearer than a furlong off, for fear of being overwhelmed by a sudden turn of the wind, which carried up into the air some of that vast pillar of ashes, which to our apprehension exceeded twice the size of St. Paul's steeple in London, and went up in a straight body to a far greater height than it; the whole air being thereabout all covered with the lightest of those ashes blown off from the top of this pillar: and from the first breaking out of the fire till its fury ceased, being 54 days, neither sun nor star were seen in all that part.

About the middle of May we again went up to the mouth, where now without any danger of fire or ashes we could take a free view both of the old and new channel of the fire, and of that great mountain of ashes cast up. That which we guessed to be the old bed or channel was a three-cornered plot of about two acres, with a crust of sciarri at the bottom,

and upon that a small crust or surface of brimstone. It was

edged in on each side with a great bank or hill of ashes, and behind and at the upper end rose up that huge mountain of the same matter. Between those two banks the fire seems

to have had its passage. At the upper end in the nook upon a little hillock of crusted sciarri was a hole about 10 feet wide, whence probably the fire issued; and it might have had several other such holes, since either crusted over or covered with ashes. At the bottom of this hole the fire was seen to flow along, and below it was a channel of fire, beneath that surface of sciarri, which being cleft a-top for some space, we had an easy and deliberate view of the metal flowing along, whose superficies might be a yard broad, though possibly it carried a greater breadth underneath, the gutter sloping. What depth it had we could not guess: it was impenetrable by iron hooks and other instruments.

Some Inquiries concerning the Salt Springs and the Way of Salt-making at Nantwich in Cheshire, answered by WILLIAM JACKSON, M. D.-[1669.]

1. WHAT is the depth of the salt springs? - The depths are various, in some places not above three or four yards; at Nantwich, the pit is full seven yards from the footing about the pit; which is guessed to be the natural height of the ground, though the bank be six feet higher, accidentally raised by accumulated rubbish or walling as they call it. In other places the springs lie much shallower; for in two places within our township the springs break up so in the meadows, as to fret away not only the grass, but part of the earth which lies like a breach at least half a foot or more lower than the turf of the meadow, and has a salt liquor oosing as it were out of the mud, but very gently.

2. What kind of country it is where the springs are, whether hilly, &c.?-Generally a low ground, yet very full of eminences, and various risings, to distinguish it from being all meadow. We have also a peculiar sort of ground in this county and some adjacent parts, which we call mosses, they are a kind of moorish boggy ground, very stringy and fat: which serves us very well for turfs, cut out like great bricks and dried in the sun.

3. How strong the water is of salt? Springs are rich or poor in a double sense; for a spring may be rich in salt, but poor in the quantity of brine it affords. Thus they have a rich brine in their chief pit at Middlewich, which yields a full fourth part of salt; yet this is so thrifty of its brine, that the inhabitants are limited to their proportions out of it, and their quantity is supplied out of pits that afford a weaker

brine. Our pit at Nantwich yields but a sixth part; but then it is plentiful.

4. What is the manner of their work?—Their manner of working is this: They have formerly boiled their brine in six leaden pans with wood-fire; upon which account they all claim their interest in the pit by the name of so many six leads walling; by which they each know their proportion; but in the memory of many they changed their six leads into four iron pans, something better than a yard square, and about six inches deep, still fitting the content of these to that of the six leads: and of late many have changed the four iron pans into two greater; and some wall but in one: but still the rulers gauge it to their old proportions.

An Account of a Halo seen at Paris: also on the Cause of these Meteors, and of Parhelias or Mock Suns. By M. HUYGENS.

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[1670.]

This halo, or circle about the sun, was observed at Paris, March 12. 1667, about nine o'clock in the morning. The diameter was 44 degrees, and the breadth of its limb about half a degree. The upper and lower part were of a vivid red and yellow, with a little purple colour, but especially the upper; the red was within the circle. The other parts appeared but whitish and of little clearness. The space within the halo was a little darker than that about it, especially towards the parts that were coloured. Besides there was seen the portion of another great circle, which touched the halo above, and whose extremities were bent downward. This portion of a circle had also its colours like those of the halo, but fainter. The height of the sun, at the beginning of the observation, was about 46 degrees. There were in the air little clouds, which somewhat tarnished the blue colour of the sky, and lessened the brightness of the sun, which seemed as in an eclipse. The weather was cold, considering the season of the year, and it was affirmed for certain, that it had frozen the night before. This halo appeared in the same beauty and splendour of colours unchanged, from nine in the morning till about half an hour past ten; after which time it became fainter and fainter, till two o'clock in the afternoon, when it ended, after it had resumed a little more force some time before it disappeared.

Halos are formed by small round grains, made up of two parts, one transparent, the other opaque, the latter being inclosed in the former, as a cherry-stone is in a cherry; many have

seen hail formed after this manner, and some of these little grains, which swim up and down in the air between us and the sun, being less distant from the axis, which extends itself from the sun to our eye, than of a certain angle, do necessarily hinder the rays, which fall on them, from coming to our eyes; since the opaque kernel is the cause that there is behind every such grain a space of a conical figure, in which the eye of the spectator being situated, cannot see the sun through that grain, though it may see it when posited elsewhere.

These arches usually touch a parhelion, because the same horizontal cylinders, which produce the arch, produce also that parhelion by means of their two round and transparent ends.

To make all these different effects of the cylinders manifest to the eye, M. Huygens produced one of glass, a foot long; and for the opaque kernel in the middle, a cylinder of wood, and the ambient space filled with water, instead of transparent ice: which cylinder being exposed to the sun, and the eye put in proper places, there were successively seen all those reflections and refractions above mentioned. Whence it might be concluded, that a great number of the like cylinders, although very small in comparison to that, being found in the air, and having the several postures that have been supposed, all the appearances of the parhelia and their circles must exactly follow.

Experiments about Respiration, by the Honourable ROBERT BOYLE.-[1670.]

NATURE having, as zoologists teach us, furnished ducks and other water-fowl with a peculiar structure of some vessels about the heart, to enable them, when they have occasion to dive, to forbear for a while respiring under water without prejudice, I thought it worth the trial, whether such birds would much better than other animals endure the absence of the air in our exhausted receiver.

We put a full grown duck into a receiver, of which she filled a third part or somewhat more, but was not able to stand in an easy posture in it; then pumping out the air, though she seemed at first to continue well somewhat longer than a hen in her condition would have done; yet within the space of one minute she appeared much discomposed, and between that and the second minute, her struggling and convulsive motions increased so much, that her head also hanging carelessly down, she seemed to be just at the point of death; from which we presently rescued her by letting in the air upon her.