Light. cies. Columna, an industrious naturalist, observes, that their light is not extinguished immediately upon the death of the animal.

P. 45.

Light from The first distinct account that we meet with of light putrid flesh. proceeding from putrescent animal flesh is that which De Visione, is given by Fabricius ab Aquapendente; who says, that when three Roman youths, residing at Padua, had bought a lamb, and had eaten part of it on Easter day 1562, several pieces of the remainder, which they kept till the day following, shone like so many candles when they were casually viewed in the dark. Part of this luminous flesh was immediately sent to Aquapendente, who was professor of anatomy in that city. He observed, that both the lean and the fat of this meat shone with a whitish kind of light; and also took notice, that some pieces of kid's flesh, which had happened to have lain in contact with it, were luminous, as well as the fingers and other parts of the bodies of those persons who touched it. Those parts, he observed, shone the most which were soft to the touch. and seemed to be transparent in candle light; but where the flesh was thick and solid, or where a bone was near the outside, it did not shine.

Works,

vol. iii.

p. 156.

After this appearance, we find no account of any other similar to it, before that which was observed by Bartholin, and of which he gives a very pompous description in his ingenious treatise already quoted. This happened at Montpelier in 1641, when a poor old woman had bought a piece of flesh in the market, intending to make use of it the day following. But happening not to be able to sleep well that night, and her bed and pantry being in the same room, she observa ed so much light come from the flesh, as to illuminate all the place where it hung. A part of this luminous flesh was carried as a curiosity to Henry Bourbon, duke of Condé, the governor of the place, who viewed it for several hours with the greatest astonishment.

This light was observed to be whitish; and not to cover the whole surface of the flesh, but certain parts only, as if gems of unequal splendour had been scattered This flesh was kept till it began to putrefy, when the light vanished; which, as some religious people fancied, it did in the form of a cross.

over it.

It is natural to expect, that the almost universal experimental philosopher Mr Boyle should try the effect of his air-pump upon these luminous substances. Ac cordingly, we find that he did not fail to do it; when he presently found that the light of rotten wood was extinguished in vacuo, and revived again on the admission of the air, even after a long continuance in vacuo; but the extinguishing of this light was not so complete immediately upon exhausting the receiver, assome little time afterwards. He could not perceive, however, that the light of rotten wood was increased in condensed air; but this, he imagined, might arise from his not being able to judge very well of the degree of light, through so thick and cloudy a glass Birch's hist. vessel as he then made use of; but we find that the light of a shining fish, which was put into a condensing engine before the Royal Society, in 1668, was rendered more vivid by that means. The principal of Mr Boyle's experiments were made in October 1667.

ii. 254.

This philosopher attended to a great variety of circumstances relating to this curious phenomenon. A.

mong other things he observed, that change of air was not necessary to the maintenance of this light; for it continued a long time when a piece of the wood was put into a very small glass hermetically sealed, and it made no difference when this tube which contained the wood was put into an exhausted receiver. This he also observed with respect to a luminous fish, which he put into water, and placed in the same circumstances. He also found, that the light of shining fishes had other properties in common with that of shining wood; but the latter, he says, was presently quenched with water, spirit of wine, a greater variety of saline mixtures, and other fluids. Water, however, did not quench all the light of some shining veal on which he tried it, though spirit of wine destroyed its virtue presently.

Light.

Mr Boyle's observation of light proceeding from flesh meat was quite casual. On the 15th of February 1662, one of his servants was greatly alarmed with the shining of some veal, which had been kept a few days, but had no bad smell, and was in a state very proper for use. The servant immediately made his master acquainted with this extraordinary appearance; and though he was then in bed, he ordered it to be immediately Birch, brought to him, and he examined it with the greatest 70. attention. Suspecting that the state of the atmosphere had some share in the production of this phenomenon, he takes notice, after describing the appearance, that the wind was south-west and blustering, the air hot for the season, the moon was past its last quarter, and the mercury in the barometer was at 29th inches.

In

Mr Boyle was often disappointed in his experiments Light from on shining fishes; finding that they did not always fishes. shine in the very same circumstances, as far as he could judge, with others which had shined before. At one time that they failed to shine, according to his expectations, he observed that the weather was variable, and not without some days of frost and snow. general he made use of whitings, finding them the fittest for his purpose. In a discourse, however, upon this subject at the Royal Society in 1681, it was asserted, that, of all fishy substances, the eggs of lobsters, after they had been boiled, shone the brightest. Olig, Jacobus observes, that, upon opening a sea- Act. Hafn polypus, it was so luminous as to startle several per- vol. v. sons who saw it; and he says, that the more putrid the p. 282. fish was, the more luminous it grew, The nails also, and the fingers of the persons who touched it, became luminous; and the black liquor which issued from the animal, and which is its bile, shone also, but with a very faint light.

Mr Boyle draws a minute comparison between the light of burning coals and that of shining wood or fish, showing in what particulars they agree, and in whatthey differ. Among other things he observes, that extreme cold extinguishes the light of shining wood, as appeared when a piece of it was put into a glass tube, and held in a frigorific mixture. He also found that rotten wood did not waste itself by shining, and that the application of a thermometer to it did not discover the least degree of heat.

Of the pho There is a remarkable shell-fish called PHOLAS, which las, a reforms for itself holes in various kinds of stone, &c. markably That this fish is luminous, was noticed by Pliny; who fish. observes,

luminous

Light observes, that it shines in the mouth of the person who eats it, and, if it touch his hands or clothes, makes them luminous. He also says that the light depends upon its moisture. The light of this fish has furnished matter for various observations and experiments to M. Reaumur, and the Bolognian academicians, especially Beccarius, who took so much pains with the subject of phosphoreal light.

Com. Bonon

M. Reaumur observes, that, whereas other fishes give light when they tend to putrescence, this is more luminous in proportion to its being fresh; that when they are dried, their light will revive if they be moistened either with fresh or salt water, but that brandy immediately extinguishes it. He endeavoured to make this light permanent, but none of his schemes suc

ceeded.

The attention of the Bolognian academicians was engaged to this subject by M. F. Marsilius, in 1724, who brought a number of these fishes, and the stones in which they were inclosed, to Bologna, on purpose for their examination.

Beccarius observed, that though this fish ceased to vol. ii. 232. shine when it became putrid; yet that in its most putrid state, it would shine, and make the water in which it was immersed luminous, when it was agitated. Galeatius and Montius found, that wine or vinegar extinguished this light; that in common oil it continued some days; but in rectified spirit of wine or urine, hardly a minute.

In order to observe in what manner this light was affected by different degrees of heat, they made use of a Reaumur's thermometer, and found that water rendered luminous by these fishes increased in light till the heat arrived to 45 degrees; but that it then became suddenly extinct, and could not be revived.

In the experiments of Beccarius, a solution of sea salt increased the light of the luminous water; a solu tion of nitre did not increase it quite so much. Salammoniac diminished it a little, oil of tartar per deliquium nearly extinguished it, and the acids entirely. This water poured upon fresh calcined gypsum, rock crystal, ceruse, or sugar, became more luminous. He also tried the effects of it when poured upon various other substances, but there was nothing very remarkable in them. Afterwards, using luminous milk, he found that oil of vitriol extinguished the light, but that oil of tartar increased it.

This gentlemen had the curiosity to try how dif ferently coloured substances were affected by this kind of light; and having, for this purpose, dipped several ribbons in it, the white came out the brightest, next to this was the yellow, and then the green; the other colours could hardly be perceived. It was not, however, any particular colour, but only light that was perceived in this case. He then dipped boards painted with the different colours, and also glass tubes, filled with substances of different colours, in water rendered luminous by the fishes. In both these cases the red was hardly visible, the yellow was the brightest, and the violet the dullest. But on the boards the blue was nearly equal to the yellow, and the green more languid; whereas in the glasses, the blue was inferior to the green.

Of all the liquors into which he put the pholades, milk was rendered the most luminous. A single pho

las made seven ounces of milk so luminous, that the faces of persons might be distinguished by it, and it looked as if it was transparent.

Air appeared to be necessary to this light; for when Beccarius put the luminous milk into glass tubes, no agitation would make it shine, unless bubbles of air were mixed with it. Also Montius and Galeatius found, that, in an exhausted receiver, the pholas lost its light, but the water was sometimes made more lu minous; which they ascribed to the rising of bubbles of air through it.

Beccarius, as well as Reaumur, had many schemes to render the light of these pholades permanent. For this purpose he kneaded the juice into a kind of paste, with flour, and found that it would give light when it was immersed in warm water; but it answered best to preserve the fish in honey. In any other method of preservation, the property of becoming luminous would not continue longer than six months, but in honey it had lasted above a year; and then it would, when plunged in warm water, give as much light as ever it had done.

Light.

Similar, in some respects, to those observations on Aa Cæsathe light of the pholas, was that which was observed riensia, vol. v. to proceed from wood which was moist, but not in a p. 485. putrid state, which was very conspicuous in the dark. That the sea is sometimes luminous, especially when Light from it is put in motion by the dashing of oars or the sea water. beating of it against a ship, has been observed with admiration by a great number of persons. Mr Boyle, after reciting all the circumstances of this appearance, as far as he could collect them from the accounts of navigators; as its being extended as far as the eye could reach, and at other times being visible only when the water was dashed against some other body; that, in some seas, this phenomenon is accompanied by some particular winds, but not in others; and that sometimes one part of the sea will be luminous, when another part, not far from it, will not be so; concludes with saying, that he could not help suspecting that these odd phenomena, belonging to great masses of water, were in some measure owing to some cosmical law or custom of the terrestrial globe, or at least of the planetary vortex.

meuts on

fishes.

Some curious observations on the shining of some Dr Beale's fishes, and the pickle in which they were immersed, experiwere made by Dr Beale, in May 1665; and had they been properly attended to and pursued, might have led to the discovery of the cause of this appearance. Having put some boiled mackerel into water, together Phil Trans with salt and sweet herbs; when the cook was, some vol. lix. time after, stirring it, in order to take out some of the P. 450. fishes, she observed, that, at the first motion, the water was very luminous; and that the fish shining through the water added much to the light which the water yielded. The water was of itself thick and blackish, rather than of any other colour; and yet it shined on being stirred, and at the same time the fishes appeared more luminous than the water. Wherever the drops of this water, after it had been stirred, fell to the ground, they shined; and the children in the family diverted themselves with taking the drops, which were as broad as a penny, and running with them about, the house. The cook observed, that, when she turned up that side of the fish that was lowest, no light came from B 2

it;

Light. it; and that, when the water had settled for some time, it did not shine at all. The day following, the water gave but little light, and only after a brisk agitation, though the fishes continued to shine as well from the inside as the outside, and especially about the throat, and such places as seemed to have been a little broken in the boiling.

Father

When in the light of the sun, he examined, with a microscope, a small piece of a fish which had shined very much the night before, he found nothing remarkable on its surface, except that he thought he perceived what he calls a steam, rather dark than luminous, arising like a very small dust from the fish, and here and there a very small and almost imperceptible sparkle. Of the sparkles he had no doubt; but he thought it possible that the steam might be a deception of the sight, or some dust in the air.

Finding the fish to be quite dry, he moistened it with his spittle; and then observed that it gave a little light, though but for a short time. The fish at that time was not fetid, nor yet insipid to the best discerning palate. Two of the fishes he kept two or three days longer for farther trial: but, the weather being very hot, they became fetid: and, contrary to his expectations, there was no more light produced either by the agitation of the water or in the fish.

Father Bourzes, in his voyage to the Indies in Bourzes's 1704, took particular notice of the luminous appearance of the sea. The light was sometimes so great, luminous that he could easily read the title of a book by it,

account of

sea water.

cause.

though he was nine or ten feet from the surface of the water. Sometimes he could easily distinguish, in the wake of a ship, the particles that were luminous from those that were not; and they appeared not to be all of the same figure. Some of them were like points of light, and others such as stars appear to the naked eye. Some of them were like globes, of a line or two in diameter; and others as big as one's head. Sometimes they formed themselves into squares of three or four inches long, and one or two broad. Sometimes all these different figures were visible at the same time; and sometimes they were what he calls vortices of light, which at one particular time appeared and disappeared immediately like flashes of lightning.

Nor did only the wake of the ship produce this light, but fishes also, in swimming, left so luminous a track behind them, that both their size and species might be distinguished by it. When he took some of the water out of the sea, and stirred it ever so little with his hand, in the dark, he always saw in it an infinite number of bright particles; and he had the same appearance whenever he dipped a piece of linen in the sea, and wrung it in a dark place, even though it was half dry; and he observed, that when the sparkles fell upon any thing that was solid, it would continue shining for some hours together.

His conjecAfter mentioning several circumstances which did tares con- not contribute to this appearance, this father observes, cerning the that it depends very much upon the quality of the water; and he was pretty sure that this light is the greatest when the water is fattest, and fullest of foam. For in the main sea, he says, the water is not everywhere equally pure; and that sometimes, if linen be dipped in the sea, it is clammy when it is drawn up again: and he often observed, that when the wake of the ship

was the brightest, the water was the most fat and glu. Light, tinous, and that linen moistened with it produced a great deal of light, if it were stirred or moved briskly. Besides, in some parts of the sea, he saw a substance like saw dust, sometimes red and sometimes yellow; and when he drew up the water in those places, it was always viscous and glutinous. The sailors told him that it was the spawn of whales; that there are great quantities of it in the north; and that sometimes, in the night, they appeared all over of a bright light, without being put in motion by any vessel or fish passing by them.

As a confirmation of this conjecture, that the more glutinous the sea water is, the more it is disposed to become luminous, he observes, that one day they took 2 fish which was called a bonite, the inside of the mouth of which was so luminous, that without any other light, he could read the same characters which he had before read by the light in the wake of the ship; and the mouth of this fish was full of a viscous matter, which, when it was rubbed upon a piece of wood, made it immediately all over luminous; though, when the moisture was dried up, the light was extinguished.

The abbé Nollet was much struck with the lumi- Abbé Nolnousness of the sea when he was at Venice in 1749; let's theory and, after taking a great deal of pains to ascertain the circumstances of it, concluded that it was occasioned by a shining insect; and having examined the water very often, he at length did find a small insect, which he particularly describes, and to which he attributes the light. The same hypothesis had also occurred to M. Vianelli, professor of medicine in Chioggia near Venice; and both he and M. Grizellini, a physician in Venice, have given drawings of the insects from which they imagined this light to proceed.

The abbé was the more confirmed in his hypothesis, by observing, some time after, the motion of some luminous particles in the sea. For, going into the water, and keeping his head just above the surface, he saw them dart from the bottom, which was covered with weeds, to the top, in a manner which he thought very much resembled the motions of insects; though, when he endeavoured to catch them, he only found some luminous spots upon his handkerchief, which were enlarged when he pressed them with his finger.

le Roi.

M. le Roi, making a voyage on the Mediterranean, Observapresently after the abbé Nollet made his observations tions of M. at Venice, took notice, that in the day time, the prow of the ship in motion threw up many small particles, which, falling upon the water, rolled upon the surface of the sea for a few seconds before they mixed with Memoires it; and in the night the same particles, as he con- Presentes, vol. iii. 144. cluded, had the appearance of fire. Taking a quantity of the water, the same small sparks appeared whenever it was agitated; but, as was observed with respect to Dr Beale's experiments, every successive agitation produced a less effect than the preceding, except after being suffered to rest a while; for then a fresh agitation would make it almost as luminous as the first. This water, he observed, would retain its property of shining by agitation a day or two; but it disappeared immediately on being set on the fire, though it was not made to boil.

This gentleman, after giving much attention to this phenomenon, concludes, that it is not occasioned by

any

any shining insects, as the abbé Nollet imagined; espe cially as, after carefully examining some of the luminous points, which he caught upon an handkerchief, he found them to be round like large pins heads, but with nothing of the appearance of any animal, though he viewed them with a microscope. He also found, that the mixture of a little spirit of wine with water just drawn from the sea, would give the appearance of a great number of little sparks, which would continue visible longer than those in the ocean. All the acids, and various other liquors, produced the same effect, though not quite so conspicuously; but no fresh agitation would make them luminous again. M. le Roi is far from asserting that there are no luminous insects in the sea. He even supposes that the abbé Nollet and M. Vianelli had found them. But he was satisfied that the sea is luminous chiefly on some other account, though he does not so much as advance a conjecture about what it is.

M. Ant. Martin made many experiments on the light of fishes, with a view to discover the cause of the light of the sea. He thought that he had reason to conclude, from a great variety of experiments, that all sea fishes have this property; but that it is not to be found in any that are produced in fresh water. Nothing depended upon the colour of the fishes, except that he thought that the white ones, and especially those that had white scales, were a little more luminous than others. This light, he found, was increased by a small quantity of salt; and also by a small degree of warmth, though a greater degree extinguished it. This agrees with another observation of his, that it depends entirely upon a kind of moisture which they had about them, and which a small degree of heat would expel, when an oiliness remained which did not give this light, but would burn in the fire. Light from the flesh of birds or beasts is not so bright, he says, as that which proceeds from fish. Human bodies, he says, have sometimes emitted light about the time that they began to putrefy, and the walls and roof of a place in which dead bodies had often been exposed, had a kind of dew or clamminess upon it, which was sometimes luminous; and he imagined that the lights which are said to be seen in burying-grounds may be owing to this cause.

From some experiments made by Mr Canton, he concludes, that the luminousness of sea water is owing to the slimy and other putrescent substances it contains. On the evening of the 14th of June 1768, he put a small fresh whiting into a gallon of sea water, in a pan which was about 14 inches in diameter, and took notice that neither the whiting nor the water, when agitated, gave any light. A Fahrenheit's thermometer, in the cellar where the pan was placed, stood at 54°. The 15th, at night, that part of the fish which was even with the surface of the water was luminous, but the water itself was dark. He drew the end of a stick through it, from one side of the pan to the other; and the water appeared luminous behind the stick all the way, but gave light only where it was disturbed. When all the water was stirred, the whole became luminons, and appeared like milk, giving a considerable degree of light to the sides of the pan; and it continued to do so for some time after it was at rest. The water was most luminous when the

fish had been in it about 28 hours; but would not give Light, any light by being stirred, after it had been in it three days.

He then put a gallon of fresh water into one pan, and an equal quantity of sea water into another; and into each pan he put a fresh herring of about three ounces. The next night the whole surface of the sea water was luminous without being stirred; but it was much more so when it was put in motion; and the upper part of the herring, which was considerably below the surface of the water, was also very bright; while at the same time the fresh water, and the fish that was in it, were quite dark. There were several very bright luminous spots on different parts of the surface of the sea water; and the whole, when viewed by the light of a candle, seemed covered with a greasy scum. The third night, the Hght of the sea water, while at rest, was very little, if at all less than before; but when stirred, its light was so great as to discover the time by a watch, and the fish in it appeared as a dark substance. After this, its light was evidently decreasing, but was not quite gone before the 7th night. The fresh water and the fish in it were perfectly dark during the whole time. The thermometer was generally above 60°.

The preceding experiments were made with sea water: but he now made use of other water, into which he put common or sea salt, till he found, by an hydrometer, that it was of the same specific gravity with the sea water; and, at the same time, in another gallon of water, he dissolved two pounds of salt; and into each of these waters he put a small fresh herring. The next evening the whole surface of the artificial sea water was luminous without being stirred; but gave much more light when it was disturbed. It appeared exactly like the real sea water in the preceding experiment its light lasted about the same time, and went off in the same manner while the other water, which was almost as salt as it could be made, never gave any light. The herring which was taken out of it the seventh night, and washed from its salt, was found firm and sweet; but the other herring was very soft and putrid, much more so than that which had been kept as long in fresh water. If a herring, in warm weather, be put into 10 gallons of artificial sea water, instead of one, the water, he says, will still become luminous, but its light will not be so strong.

It appeared by some of the first observations on this subject, that heat extinguishes the light of putrescent substances. Mr Canton also attended to this circumstance; and observes, that though the greatest summer heat is well known to promote putrefaction, yet 20 degrees more than that of the human blood seems to hinder it. For putting a small piece of a luminous fish into a thin glass ball, he found, that water of the heat of 118 degrees would extinguish its light in less than half a minute; but that, on taking it out of the water, it would begin to recover its light in about 10 seconds; but it was never afterwards so bright as before.

Mr Canton made the same observation that Mr Ant. Martin had done, viz. that several kinds of river fish could not be made to give light, in the same circumstances in which any sea fish became luminous. He says, however, that a piece of carp made the water very luminous,

huminous, though the outside, or scaly part of it, did not shine at all.

For the sake of those persons who may choose to repeat his experiments, he observes, that artificial sea water may be made without the use of an hydrometer, by the proportion of four ounces avoirdupois of salt to seven pints of water, wine measure.

A very elaborate paper on the subject by Dr Hulme appeared in the Philosophical Transactions for 1800, to which we refer our readers, and to CHEMISTRY, p. 451.

From undoubted observations, however, it appears, that in many places of the ocean it is covered with lu minous insects to a very considerable extent. M. Da gelet, a French astronomer who returned from the Terra Australis in the year 1774, brought with him several kinds of worms which shine in water when it is set in motion; and M. Rigaud, in a paper inserted (if we are not mistaken) in the Journal des Sçavans for the month of March 1770, affirms, that the luminous surface of the sea, from the port of Brest to the Antilles, contains an immense quantity of little, round, shining polypuses of about a quarter of a line in diameter. Other learned men, who acknowledge the existence of these luminous animals, cannot, however, be persuaded to consider them as the cause of all that light and scintillation that appear on the surface of the ocean they think that some substance of the phosphorus kind, arising from putrefaction, must be admitted as one of the causes of this phenomenon. M. Godehoue has published curious observations on a kind of fish called in French bonite, already mentioned; and though he has observed, and accurately described, several of the luminous insects that are found in sea-water, he is, nevertheless, of opinion, that the scintillation and flaming light of the sea proceed from the oily and greasy substances with which it is impregnated.

The abbé Nollet was long of opinion, that the light of the sea proceeded from electricity (A); though he afterwards seemed inclined to think, that this phenomenon was caused by small animals, either by their luminous aspect, or at least by some liquor or effluvia which they emitted. He did not, however, exclude other causes; among these, the spawn or fry of fish deserves to be noticed. M. Dagelet, sailing into the bay of Antongil, in the island of Madagascar, observed a prodigious quantity of fry which covered the surface of the sea above a mile in length, and which he at first took for banks of sand on account of their colour; they exhaled a disagreeable odour, and the sea had appeared with uncommon splendour some days before. The same accurate observer, perceiving the sea remarkably luminous in the road of the Cape of Good Hope during a perfect calm, remarked, that the oars of the canoes produced a whitish and pearly kind of lustre; when he took in his hand the water which contained this phosphorus, he discerned in it, for some minutes, globules of light as large as the heads of pins. When he pressed these globules, they appeared to his touch like a soft and thin pulp; and some days after the sea was covered

To putrefaction, also, some are willing to attribute that luminous appearance which goes by the name of ignis fatuus, to which the credulous vulgar ascribe very Ignis faextraordinary and expecially mischievous powers. Ittuus. is most frequently observed in boggy places and near rivers, though sometimes also in dry places. By its appearance benighted travellers are said to have been sometimes misled into marshy places, taking the light which they saw before them for a candle at a distance; from which seemingly mischievous property it has been thought by the vulgar to be a spirit of a malignant nature, and been named accordingly Will with a wisp, or Jack with a lanthorn; for the same reason also it probably had its Latin name ignis fatuus.

This kind of light is said to be frequent about burying places and dunghills. Some countries are also remarkable for it, as about Bologna in Italy, and some parts of Spain and Ethiopia. Its forms are so uncertain and variable that they can scarce be described, especially as few philosophical observers ever had the good fortune to meet with it. Dr Derham, however, happened one night to perceive one of them, and got so near that he could have a very advantageous view of it. This is by no means easy to be obtained; for among other singularities of the ignis fatuus, it is observed to avoid the approach of any person, and fly from place to place as if it was animated. That which Dr Derham observed was in some boggy ground betwixt two rocky hills; and the night was dark and calm; by which means, probably, he was enabled to advance within two or three yards of it. It appeared like a complete body of light without any division, so that he was sure it could not be occasioned by insects, as some have supposed; the separate lights of which he could not have failed to distinguish, had it been occasioned by them. The light kept dancing about a dead thistle, till a very slight motion of the air, occasioned, as he supposed, by his near approach to it, made it jump to another place; after which it kept flying before him as he advanced. M. Beccaria endeavoured to procure all the intelligence he could concern. ing his phenomenon, by inquiring of all his acquaintance who might have had an opportunity of observing it. Thus he obtained information that two of these lights appeared in the plains about Bologna, the one to the north, and the other to the south, of that city, and were to be seen almost every dark night, especially that to the eastward, giving a light equal to an ordinary faggot. The latter appeared to a gentleman of his acquaintance as he was travelling; moved constantly before him for about a mile; and gave a better light than a torch which was carried before him. Both these appearances gave a very strong light, and were constantly in motion, though this various and uncertain. Sometimes they would rise, sometimes sink; but commonly they would hover about six feet from the ground; they would also frequently disappear on a sudden,