passages in a mine, which branch out from the main grove, a round thing hangs about as big as a football, covered with a thin skin. If this be broken, the damp immediately spreads, and suffocates all that are near. But sometimes they contrive to break it at a distance; after which they purify the place with fire. The forth is the fire-damp; a vapour, which if touched by the flame of a candle, takes fire, and goes off like gunpowder. And yet some who have had all their clothes burnt off by one of these, and their flesh torn off their bones, at the very time felt no heat at all, but as it were a cool air.

Sir James Lowther, having collected some of the air in bladders, brought it up to London. Being let out at the orifice through a tobacco-pipe, it would take fire at the flame of a candle. And even this is emitable by art. Most metals emit sulphureous vapours, while they are dissolving in their several menstruums. Iron, for instance, while it dissolves in oil of vitrol, emits much sulphureous vapour. If this be received into a bladder, and afterwards let out in a small stream, it takes fire just in the same manner as the natural vapour.

This experiment explains one cause of earthquakes and volcanos; since, it appears hence, that nothing more is necessary to form them, than iron mixing with vitriolic acid and water. Now iron is generally found accompanied with sulphur and sulphur consists of an inflammable oil, and an acid like oil of vitriol.

This acid in the bowels of the earth, being diluted with a little water, becomes a menstruum to iron, with a violent effervescence and an intense heat. The air coming from this mixture is extremely rarefied, and the more it is compressed by the incumbent earth, so much the more its impetus will be increased to an unlimited degree. Nor does there need fire to set these vapours to work. The air in the bladder, if it be much heated, will of itself take fire, as soon as it is brought into contact with the external air.

Other damps are sometimes as mortal as those in mines. In the year 1701, a mason being at work in the city of Rennes, near the brink of a well, let his hammer fall into it. A labourer who was sent down for it, was suffocated before he reached the water. A second sent to draw him up, met with the same fate. So did a third. At last a fourth, half drunk, was let down with a charge to call out immediately, if he felt any inconvenience. He did call, as soon as he came near the water, and was drawn up instantly. Yet he died in three days, crying out, he felt a heat, which scorched his entrails. Yet the three carcases being drawn up with hooks, and opened, there appeared no cause of their death.

The same historians relate, that a baker of Chartres, having carried seven or eight bushels of brands out of his oven, into a cellar thirty-six stairs deep, his son, a strong young fellow, going with more, his candle went out on the middle of the stairs. Having lighted it afresh, he no sooner got into the cellar, than he cried for help, and they heard no more of him. His brother, an able youth, ran down, cried, "I am dead," and was heard no more. He was followed by his wife, and she by a maid, and still it was the same. Yet a hardy fellow re-olved to go and help them: he cried to, and was seen no more. A sixth man desired a hook to draw some of them out. He drew up the maid, who fetched a sigh and died. Next day one undertook to draw up the rest, and was let down on a wooden horse with ropes, to be drawn up whenever he should call. He soon called, but the rope breaking, he fell back again, and was awhile after drawn up dead. Upon opening him, the membranes of the brain were extremely stretched, his lungs spotted with blood, his intestines swelled as big as one's arm, and red as blood, and all the muscles of his arms, thighs and legs, torn and separated from their bones.

Whence this strange difference should arise, that the vapours of some mines catch fire with a spark, and others only with a flame, is a question that we must content to leave in obscurity, till we know more of the nature both of mineral vapour and fire. This only we may observe, that gunpowder will fire with a spark, but not with the flame of a candle: on the other hand, spirits of wine will flame like a candle, but not with a spark. But even here the cause of this difference remains a secret.

A like instance of the fatal nature of foul air, happened at Boston, in New-England. Mr. Adams and his servant being employed to repair a pump, uncovered the well, and Mr. Adams went down by a rope; but he had not gone six feet before he dropt suddenly without speaking a word, to the upper part of the joint of the pump, where being supported about a minute, and breathing very short, he then fell to the bottom, without any signs of life. His servant hastily went down to help his master; but at the same distance from the top, was struck, and without discovering any signs of distress, fell to the bottom. The workmen prepared a third, with a tackle about the waist. On his decent, he was quickly speechless and sen eless. Though he made no sign, they drew him up. He was the very picture of death, but by the use of proper means recovered. He remembered nothing of what had passed. The other bodies when taken up, had all the marks of a violent death.

An account of the Phenomenon of Ignis Fatuus, vulgarly called, will-with-the-wisp, or the jack-a-lantern.

IGNIS FATUUS, vulgarly called will-with-the-wisp, is chiefly seen in dark nights, irregularly moving over meadows, marshes, and other moist places. It seems to be a viscous exhalation, which being kindled in the air, reflects a kind of thin flame in the dark, though without any sensible heat. It is often found to fly along rivers or hedges, probably because it there meets with a stream of air to direct it. In Italy there are luminous appearances, nearly resembling these, which on a close inspection have been found to be no other than swarms of shining flies.

In all the territories of Bologna, these fiery appearances are common. There are some places where one may be almost sure of them every dark night, as near the Bridge Della Salcarata, and in the fields of Bagnara; these are large : sometimes equal to the light of a faggot, rarely less than that of a link. That at Bagnara not long since kept a gentleman company for a mile, moving just before him, and casting a stronger light on the road than the link he had with him.

All of them resemble a flame, and are continually in motion, but the motion is various and uncertain. In winter, when the ground is covered with snow, they are most frequent of all. Nor does rain hinder them: nay, in wet weather they give the strongest light; wind also does not disturb them. As they are not hindered by wet, and set nothing on fire, though ever so combustible, may it not reasonably be supposed, that they have some resemblance to that kind of phosphorus, which shines indeed in the dark, yet does not burn like common fire?

The following experiments shew a little more of the nature of this strange substance.

Salt of phosphorus, kept in a vitrifying heat, at last runs into a perfect glass. What a wonderful subject is this? And how surprising it is, that so inflammable a body should become glass! Here then is a perfect transmutation of bodies: the phosphorus being transmuted into a transparent glass of a blueish green coming nearer the hardness of a diamond, than any other glass whatever. And the glass is in the very same quantity with the phosphorus, which produces it ounce for ounce.

Another odd circumstance relating to phosphorus, is, cut it small, or scrape it with a knife, and lay it on a glass dish in moist air. In a week it dissolves into a liquid, near eighty times its original weight. This liquid is the same in all respects, with that which comes from the sublimed flowers by deflagration. And this may be turned into the same glass with the original phosphorus.

One of the most singular kinds of lambent flames is that discovered at certain times on sea-water. Where the ship goes swiftly in the night, in many seas the whole breaking of the water will appear behind it, as if on fire, sparkling and shining all the way that it moves from the ship.

It is in this part as bright and glittering as if the moon shone upon it, and chiefly when there is neither moon nor stars, nor any light in the lanterns. But it is not always the same: sometimes it is scarce perceivable, sometimes very vivid and bright. Sometimes it is only just behind the ship, sometimes it spreads a great way on each side. It commonly reaches thirty or forty feet from the stern of the ship, but is fainter as it is farther off. At the stern it is often so bright, that a person on deck may see to read by it. The luminous water that follows the ship is sometimes distinct from the rest of the surface. Sometimes it is so blended with the adjacent water, that the appearance is confused. The luminous matter seems composed of small sparkles, which are sometimes in the figure of a star, sometimes it forms globules, without any radiations from them. These are, some of the size of a large pin's head; some larger, even to a foot in diameter. Sometimes the luminous matter is in ablong squares, of three or four inches. When the ship goes swiftly, these figures all combine and form a sort of luminous whirlpool. Nor does a ship only, but whatever moves swift through the sea, cause the same appearance. Large fish when they swim near the surface, leave a luminous road between them. So have a number of fish moving together. And sometimes the throwing out a rope, or any thing that breaks the surface of the water, will render it luminous. If sea-water be taken up, and placed in a vessel, as soon as it is stirred, it will sparkle: and if a linen rag be dipped in sea water, and hung up, when it is thoroughly dried, it will appear luminous on being rubbed in the dark; and when half dry, it need only be shook, to shew a great number of sparkles. When these sparkles are once formed, and fall on any solid body, they will last a considerable time. If they remain on the water, they will soon go out.

The waves beating against the rocks or shore, yea, or against one another, will occasion the same appearance, and often yield a long course of light the whole night. In the Brasils the shores often seem all on fire, by the waves dashing against them. In general, the thicker and fouler the seas are, the more of this light they afford. In many places the sea is covered with a yellowish matter like sawdust, which seems to be the excrement of some sea-animal. The water where this is found, gives more light, upon moving, than any other.

Some parts of the northern seas are covered with this, for several leagues together, and this is often luminous all over in the night, though not stirred by any thing moving through it.