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By Samuel Williams, A. M.
Hollis Professor of Mathematics and Philosophy
in the University at Cambridge
The best method to promote the knowledge and science of nature, is to proceed by way of observation and experiment. The general course, productions, and laws of nature, should be carefully and steadily attended to: and when any new phenomena appear, all the circumstances and effects, relating to them, should be particularly noted and collected. In this way we shall be most likely to arrive at the knowledge of their causes: or, at least, we shall prepare those materials which may enable posterity to determine, with certainty and precision, on what at present may be but imperfectly understood.
With this view, I shall endeavour to lay before the Society, as particular an account as I can collect, of the uncommon darkness which took place in the states of New-England.
The time of this extraordinary darkness, was May 19, 1780. It came on between the hours of ten and eleven, A.M. and continued until the middle of the next night; but with different appearances at different places. As to the manner of its approach it seemed to appear first of all in the S. W. The wind came from that quarter, and the darkness appeared to come on with the clouds that came in that direction. The degree to which the darkness arose, was different in different places. In most parts of the country it was so great, that people were unable to read common print — determine the time of day by their clocks p235 or watches — dine — or manage their domestic business, without the light of candles. In some places, the darkness was so great, that persons could not see to read common print in the open air, for several hours together: but I believe this was not generally the case. The extent of this darkness was very remarkable. Our intelligence, in this respect, is not so particular as I could wish: but from the accounts that have been received, it seems to have extended all over the New-England states. It was observed as far east as Falmouth. — To the westward, we hear of its reaching to the furthest parts of Connecticut, and Albany. — To the southward, it was observed all along the sea-coasts: — and to the north, as far as our settlements extend. It is probable it extended much beyond these limits, in some directions: but the exact boundaries cannot be ascertained by any observations that I have been able to collect. With regard to its duration, it continued in this place at least fourteen hours: but it is probable this was not exactly the same in different parts of the country. The appearance and effects were such as tended to make the prospect extremely dull and gloomy. Candles were lighted up in the houses; — the birds having sung their evening songs, disappeared, and became silent; — the fowls retired to roost; — the cocks were crowing all around, as at break of day; — objects could not be distinguished but at a very little distance; and every thing bore the appearance and gloom of night.
Such were the general appearances or phenomena of this extraordinary darkness. I shall now mention such particular observations as I have been able to collect, which were either made on this phenomenon, or seem to relate to it.
p236 With regard to the state of the atmosphere preceding this uncommon darkness, it was universally observed for several days before, that the air appeared to be full of smoke and vapour. The sun and the moon appeared remarkably red in their colour, and divested of their brightness and lucid appearance: and this obscuration increased as they approached nearer to the horizon. This was observed to be the case in almost all parts of the New‑England states, for four or five days preceding the 19th of May. The winds had been variable; but chiefly from the S. W. and N. E. The thermometer from 40° to 55°. The barometer rather high for this part of America, — from 29 inches 80, to 30 inches 50. The weather had been fair and cool for the season.
As to the state of the atmosphere when the darkness came on, it was observable, that the weight or gravity of it was gradually decreasing the bigger part of the day. This may be inferred from the observations that were made in this place by the Rev. Professor Wigglesworth, and Mr. Gannett. At 12h. they found the mercury in the barometer stood at 29 inches 70. At 12h.30′, the mercury had fallen the 1⁄ part of an inch. At 1h. it was at 29 inches 67. At 3h. it was at 29 inches 65. At 8h.8′ it was at 29 inches 64. I made a course of barometrical observations similar to these, at the same time, in a different part of the state. I was then at Bradford, •about thirty miles north of this place, nearly under the same meridian, or rather a little to the east. At 6h. A.M. I found the mercury in the barometer 28 inches 82. As soon as the darkness began to appear uncommon, I observed the barometer again, and found the mercury at 29 inches 68: this was at 10h.20′. At 10h.45′, the darkness arose to its greatest degree in that part of the country; and the mercury was then at 29 inches 67. The darkness p237 continued in the same degree for an hour and a half. At 12h.15′ the mercury had fallen to 29 inches 65; and in a few minutes after this, the darkness began to abate. The mercury remained in this state until evening, without any sensible alteration. At 8h.30′, it seemed to have fallen a little; but so small was the alteration, that it was attended with some uncertainty; nor could I preceiveº that it stood any lower at 11h.30′.
Both these barometers appear to be very good instruments. That used in this place was made by Champney: that which I used was made by Nairne: and they may both be depended on as to the accuracy of their construction. It may, however, be proper to observe, that the house where I made my observations, stood at least •forty or fifty feet higher than that in which the observations were made here.
And from these observations it is certain, that on the day when the darkness took place, the weight or gravity of the atmosphere was gradually decreasing through the whole day.1
The colour of objects that day, was also worthy of remark. It is mentioned, in the observations made by the gentleman here, that "the complexion of the clouds was compounded of a faint red, yellow, and brown; and that, during the darkness, objects, which commonly appear green, were of the deepest green, verging to blue; and that those which appear white, were highly tinged with yellow." Much the same observation was pretty generally made. Almost every object appeared to me to be tinged with yellow rather than with any other p238 other colour. This I found to be the case with every thing I held up to view, whether near, or remote from the eye.
Another thing that deserves our attention is, the nature and appearance of the vapours that were then in the atmosphere. Early in the morning, the weather was cloudy: the sun was but just visible through the clouds, and appeared of a deep red, as it had for several days before. In most places thunder was heard several times in the morning. The clouds soon began to rise from the S. W. with a gentle breeze; and there were several small showers before eight o'clock: and in some places there were showers at other times, throughout the day. The water that fell was found to have an uncommon appearance, being thick, dark and sooty. A gentleman, who was then at Ipswich, observes, that "he found the people much surprized with the strange appearance and smell of the rain-water which they had saved in tubs. Upon examining the water, I found (says he) a light scum over it, which rubbing between my thumb and finger, I found to be nothing but the black ashes of burnt leaves: the water gave the same strong sooty smell which we had observed in the air." The same appearance was observed in many other places: and it was very remarkable on Merrimack-River. Large quantities of scum, or black ash, were found floating upon the surface of the water, that day. In the night, the wind veered round to the N. E. and drove it towards the south shore. When the tide fell, it lay along the shore at the width of •four or five inches. This I found to be the case for •five or six miles; — and probably it was the case for many more. I examined a considerable quantity of this matter; and in taste, colour and smell, it very plainly appeared to be nothing more than what the gentleman observed at Ipswich, p239 — the black ashes of burnt leaves, without any sulphureous, or other mixtures.2
Being apprehensive whether there was not some uncommon matter in the air that day, I put out several sheets of clean paper in the air and rain. When they had been out for four or five hours, I dried them by the fire. They were much sullied, and became dark in their colour; and felt as if they had been rubbed with oil or grease. But upon burning them, there was not any appearance of sulphureous or nitrous particles.
The motion and situation of the vapours in the atmosphere, was also worthy of notice. In most places it was very evident that the vapours were descending from the higher parts of the atmosphere towards the surface of the earth. A gentleman, who was then at Pepperrell,3 mentions a very curious observation, as to their ascent and situation. "About nine o'clock (says he) in the morning, after a shower, the vapours rose from the springs in the low lands, in great abundance. I took notice of one large column that ascended with great rapidity, to a considerable height above the highest hills, and soon spread into a large cloud; then moved off a little to the westward. A second cloud was formed in the same manner, from the same springs, but did not ascend so high as the first: and a third was formed from the same places, in less than a quarter of an hour after the second. About three quarters of an hour after nine o'clock, these clouds exhibited a very romantic appearance. The upper cloud appeared of a redishº colour: the second appeared, p240 in some places, green; in others, blue; and in others, of an indigo colour: the third cloud appeared almost white." One of the gentlemen who observed here, mentions a circumstance of somewhat a singular nature. — "While the darkness continued (says he) the clouds were in quick motion, interrupted, skirted one over another; so as apparently, and I suppose really, to form a considerable number of strata: the lower stratum of an uniform height as far as visible; — that height conceived to be very small from the finall extent of the visible horizon, and from this circumstance observed in the evening: — Being in the street, I saw a person with a lighted torch, which occasioned a reflection of a faint red light, similar to a faint Aurora Borealis, at a small height above my head. The height at which the reflection appeared to be made, was not more than •from twenty to thirty feet." — And it was generally remarked, that the hills might be seen at a distance in some directions, while the intermediate spaces were greatly obscured and darkened.
From these observations, it seems as if the vapours, in some places, were ascending; in most, descending; and in all, very near to the surface of the earth. To this we may add, that during the darkness, objects appeared to cast a shade in every direction: and that, in many places, there were several appearances or corruscationsº in the atmosphere, not unlike the Aurora Borealis: but I do not find that there were any uncommon appearances of the electric fire any where observed that day.4
p241 Having mentioned the phenomena, with such observations upon them, as I have been able to collect, I shall now endeavour to account for the cause of this unusual appearance.
From the observations that have been mentioned, we may conclude with much certainty, that the atmosphere, on the 19th of May, was charged with an uncommon quantity of vapour. That this was the case, is evident from the large quantity of smoke and vapour that appeared in the atmosphere for several days before; which was so great, as to darken the sun and moon, and render all objects, at a distance, of a dull and very hazy appearance. It was also evident, from the descent of those large quantities of soot, or black ashes, which, through a long extent of country, were found mingled with the rain that fell, and floating on the surface of the waters. And the cause from whence the uncommon quantity of these vapours was derived, is easily ascertained. It is well known, that in this part of America, it is customary to make large fires in the woods, for the purpose of clearing the lands in the new settlements. This was the case this spring, in a much greater degree than is common. In the county of York, in the western parts of the state of New-Hampshire, in the western parts of this state, and in Vermont, uncommonly large and extensive fires had been kept up. The people in the new towns had been employed in clearing up their lands in this way, for two or three weeks before: and some large and extensive fires had raged in the woods for several days before they could be extinguished. In addition, therefore, to what arises from evaporation, and those exhalations which are constant and natural, a much larger quantity of vapour arose from those large and numerous fires, which extended all around our frontiers. As the weather had been clear, the p242 air heavy, and the winds small and variable for several days; the vapours, instead of dispersing, must have been rising and constantly collecting in the air, until the atmosphere became highly charged with an uncommon quantity of them.
A large quantity of the vapours, thus collected in the atmosphere, on the 19th of May, were floating near the surface of the earth. Wheresoever the specific gravity of any vapour is less than the specific gravity of the air, by the laws of fluids, such a vapour will ascend in the air. Where the specific gravity of a vapour, in the atmosphere, is greater than that of the air, such a vapour will descend: and where the specific gravity of the vapour and air are the same, the vapour will then be at rest, — floating or swimming in the atmosphere, without ascending or descending. From the barometrical observations it appears, that the weight or gravity of the atmosphere was gradually growing less, from the morning of the 19th of May, until the evening. And hence the vapours, in most places, were descending from the higher parts of the atmosphere, towards the surface of the earth. From the observation made at Pepperrell, it appears, that in some places the vapours were ascending, until they arose to an height in which the air was of the same specific gravity; where they instantly spread, and floated in the atmosphere: — and this height was not much above the adjacent hills. From these observations, we are leadº to conclude, that the place where the vapours were balanced, or became of the same specific gravity as the air, must have been very near the surface of the earth. And hence we may observe,
That such a large quantity of vapour, floating in the atmosphere, near the surface of the earth, might be sufficient to produce p243 all the phenomena that were observed May 19, 1780. — Thus the direction in which the darkness came on, would be determined by the direction of the winds; which accordingly was observed to be from the S. W. The degree of the darkness would depend on the density, colour, and situation of the clouds and vapour; and the manner in which they would transmit, reflect, refract, or absorb the rays of light. The extent of the darkness would be as great as the extent of the vapour: and the duration of it would continue until the gravity of the air became so altered, that the vapours would change their situation, by an ascent or descent. All which particulars will, I think, be found to agree very exactly with the observations that have been mentioned. Nor does the effect of the vapours, in darkening terrestrial objects, when they lay near the surface of the earth, appear to have been greater than it was in darkening the sun and moon, when their situation was higher in the atmosphere.
Upon the whole, it is evident, that the atmosphere was charged, in a high degree, with vapours; and that these vapours were of different densities, and occupied different heights. By this means the rays of light falling upon them, must have suffered a variety of refractions and reflections; and thereby become weakened, absorbed, or so far reflected, as not to fall upon objects on the earth in the usual manner. And as the different vapours were adapted by their nature, situation, or density, to absorb, or transmit, the different kind of rays, so the colours of objects would appear to be affected by the mixture and prevalency of those rays that were transmitted through so uncommon a medium.
p244 In what has been said, I have endeavoured to explain what I take to be the cause of the late unusual darkness. I would not, however, be understood to assert, that there could not be any other causes or circumstances which might join to produce this unusual appearance. Possibly there might be causes and circumstances of this nature, of which we have no suspicion. But as the uncommon quantity and situation of the vapours in the atmosphere might be sufficient to account for the phenomena, it appears to me to be unnecessary to look out for other causes, or to go into a particular examination of the various conjectures that have been advanced upon this subject.
It may not be amiss to observe, that such appearances, and from the same cause, have been observed before, in this part of America. In the Philosophical Transactions, No. 423, there is an account of a remarkable darkness, which took place October 21, 1716, O. S. It is said, "The day was so dark, that people were forced to light candles to eat their dinners by. Which could not be from any eclipse, the solar eclipse being the 4th of that month." This observation was made by Mr. Robie, a man of great ingenuity, and formerly a Tutor in the University: but there is nothing said as to the cause, or any other particulars. Several persons have informed me, that they remember an uncommon darkness in the year 1732, August 9, O. S. and which was afterward found to be occasioned by an uncommon fire in Canada. It is to be wished, that we could find something more particular upon this subject.
There was also a remarkable darkness at Detroit, October 19, 1762, much like that of May 19; of which we have this account, by the Rev. James Stirling, Phil. Trans. for 1763, vol. LIII p63.
"Tuesday last, being the 19th inst. (i.e. of p245 October) we had almost total darkness for the most of the day. I got up at day break. About than minutes later, I observed it got no lighter than before. The same darkness continued until nine o'clock, when it cleared up a little. We then, for the space of about a quarter of an hour, saw the body of the sun, which appeared as red as blood, and more than three times as large as usual. The air, all this time, which was very dense, was of a dirty yellowish colour. I was obliged to light candles to see to dine, at one o'clock, notwithstanding the table was placed close by two large windows. About three, the darkness became more horrible; which augmented until half past three, when the wind breezed up from the S. W. and brought on some drops of rain, or rather sulphur, and dirt; for it appeared more like the latter than the former, both in smell and quality. I took a leaf of clean paper, and held it out in the rain, which rendered it black whenever the drops fell upon it; but, when held near the fire, turned to a yellow colour; and when burned, it fizzed on the paper like wet powder. During this shower, the air was almost suffocating with a strong sulphureous smell. — It cleared up a little after the rain.
"There were various conjectures about the cause of this natural incident. The Indians, and the vulgar among the French, said, that the English, which lately arrived from Niagara in the vessel, had brought the plague with them. Others imagined, it might have been occasioned by the burning of the woods: but I think it most probable, that it might have been occasioned by the eruption of some volcano, or subterraneous fire, whereby the sulphureous matter may have been emitted in the air, and contained therein, until, meeting with p246 some watery clouds, it has fallen down together with the rain."
We have another account of this phenomena,º in a letter from an officer, who was then at Detroit, to a friend at Wilmington, in Pennsylvania.
The 19th of this month, (October, 1762) was the most extraordinary dark day, perhaps, ever seen in the world. At nine in the morning, it was scarce lighter than at break of day, and so continued till about twelve o'clock, — the air being very full of smoke, accompanied with a strong smell, as of wood, straw, and other combustibles, when burning. At half an hour after one, it was so dark that we were obliged to light candles to dine by. At this time it rained a little; with which fell a quantity of black particles, like ashes, as turned every thing it fell upon black. Even the river (which is twice as wide as Christiana in Pennsylvania) was covered with black froth; which, when scummed off the surface, resembled the lather of soap, with this difference, that it was (and as black as ink) more greasy. At seven in the evening, the air was more clear, and the disagreeable smell was now almost gone. We have since been informed, by people who were •twenty miles from hence that day, that the darkness, rain, and smell, was the same with them."
There does not appear to have been any thing to support the conjecture of a volcano, subterraneous fires, and sulphureous matter. In all other particulars, the phenomena agree to those that were observed among us, and seem to be derived from the same cause.
Felix, qui potuit rerum cognoscere causas,
Atque metus omnes et inexorabile fatum
Subjecit pedibus. –––––––––a
2 The same was observed at Concord and Dover in New-Hampshire: at Berwick, and many other places in this state.
3 Mr. Eames, a Tutor in the University.
4 In several accounts it was also mentioned, that a number of small birds were found suffocated by the vapour. "A number were found dead in several of the new towns, round the houses; and some flew into the houses, as I have been told by eye-witnesses." Extract of a letter from Dover, in New-Hampshire.
a Vergil, Georgics, II.490‑492 (or English translation). One of the best-known tags in all of Latin literature, it was nonetheless a very apt one to close with: many people at the time were scared and entertained the most unreasonable opinions as to the "Day of Darkness". Rather than the Day of Judgment descending on the newly independent American States, however, it seems to have been big woods fires to the west, as all but outright affirmed by our author: fortunate are we indeed when we know the causes of things and can then trample underfoot every fear, as well as unavoidable destiny.
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