coach passing moderately over frozen ground. Some, who were in their houses, at first thought their chimneys were on fire. The sky was clear. The weather was uncommonly mild and pleasant, with scarcely a breath of air.

Other slight shocks of earthquakes have occurred at different times in various parts of the New England States.

THE DARK DAY.

The 19th day of May, 1780, is denominated "The Dark Day." Soon after that period, various persons endeavoured to account for the extraordinary phenomenon. Perhaps no one gave a more satisfactory solution than that contained in a letter written in 1785, by Dr. Samuel Tenney, then of Exeter, N. H., communicated to the Historical Society, and published by them, Vol. I. p. 95. A copy of which follows, viz.

Although the uncommon darkness which attracted the attention of all ranks of people in this part of the country, on the 19th May, 1780, was a phenomenon which several gentlemen of considerable literary abilities have endeavoured to solve, yet I believe you will agree with me, that no satisfactory solution has yet appeared. But it does not thence follow, that none can be given. That it was supernatural was never supposed but by the ignorant and superstitious; it must then admit of a rational and philosophical explanation The following, therefore, is submitted to that candor with which a true philosopher will examine every modest attempt to extend our knowledge of nature, and to explain her operations. Should it not prove satisfactory, it may at least excite you to an attempt that shall be more successful.

"You will readily recollect, that previously to the commencement of the darkness, the sky was overcast with the

common kind of clouds, from which there was, in some places, a light sprinkling of rain. Between these and the earth, there intervened another stratum, to appearance of very great thickness. As this stratum advanced, the darkness commenced, and increased with its progress till it came to its height; which did not take place till the hemisphere was a second time overspread. The uncommon thickness of this second stratum was probably occasioned by two strong currents of wind from the southward and westward, condensing the vapors, and drawing them in a northeasterly direction. I remember this observation was made by an anonymous writer in one of the public papers soon after the event.

"As I set out the next day, from my father's, in Rowley, to join my regiment in New Jersey, I had an opportunity to inform myself what were the appearances in different parts of the country, between here and Pennsylvania. The result of my inquiries on that journey, and after my return, was, that the darkness was most gross in the county of Essex, the lower part of the State of New Hampshire, and the old Province of Maine. In Rhode Island and Connecticut it was not so great, and still less so in New York. In New Jersey, the second stratum of clouds was observed, but not of any great thickness; nor was the darkness very uncommon. In the lower parts of Pennsylvania, if my recollection does not fail me, no extraordinary appearance was noticed. Through this whole extent, the lower stratum had an uncommon brassy hue, while the earth and trees were adorned with so enchanting a verdure as could not escape notice, even amidst the unusual gloom that surrounded the spectator. This gradual increase of the darkness from southwest to northeast, which was nearly the course of the clouds, affords a pretty good argument in favor of the supposition, that they were condensed by two strong currents of wind, blowing in different directions. To these two strata of clouds we may, without hesitation, impute the extraordi

nary darkness of the day. Let us now examine how they effected it.

"We have, unhappily, no method of exactly comparing different degrees of light, that will apply in all cases. We cannot, therefore, determine the proportion which the light of a common rainy day bears to that of the clear sun. It is probably not so considerable as may be supposed. We may make a kind of estimate of it, sufficient for our purpose, in the following way.

"Upon a superficial consideration we should not, perhaps, suppose that the light of the full moon was in a much less proportion to that of the sun, than as that of one to one thousand. But this conjecture would be exceedingly erroneous, as will appear from the following rough calculation. The light proceeding from a luminous body is, at different distances, always in an inverse ratio of the squares of those distances. The moon is nearly 217 of her semi-diameters distant from the earth, the square of which number is a little above 47,000. Now supposing the earth and moon were, at the full of the latter, equidistant from the sun, and received equal proportions of light from him; supposing also, that the surface of the moon was in every way a perfect reflector, the above number would give the exact proportion between the light of the sun and full moon. In other words, the light of the sun would be to that of the full moon as 47,000 to 1. But the moon at the full is considerably further distant from their common source of light than the earth is, and must receive less light in proportion. Further, the moon, instead of being a perfect reflector in every part, reflects at best very imperfectly, and from a considerable portion of her surface, scarce any at all. These things considered, we cannot suppose that the light of the full moon bears a greater proportion to that of the sun than as 1 to 100,000.

We have here compared two degrees of light, which are familiar to us. With these we can compare the light we

enjoy in a common rainy day, which is equally so. This, however, can be only by conjecture, and it is not necessary for our purpose that it should be a very happy one. We will suppose the light of a common cloudy day, just before it rains, to be 10,000 times as great as the full moon, or 10 times less than that of the sun in a clear atmosphere. To put it beyond a doubt, however, that this is a modest postulatum, we will take another method to ascertain it, which, perhaps, (had it struck my mind sooner,) might have precluded the necessity of the preceding calculation. Supposing a tight room to face the sun when at a small height above the horizon, the degree of light in it will bear the same proportion to the light without doors, as the glass in that front (all other windows and doors being closed,) bears to a section of the room perpendicular to the sun's rays. For instance, if the glass is to the perpendicular section as 1 to 8, the light in the room would bear that proportion to the light without. This, however, is upon the supposition that the glass should transmit all the incident rays, which is not the fact; for a very considerable part of them is reflected; probably such a proportion as to reduce the light in the room to a twelfth part of that without doors. A very great disproportion this; but I believe you will allow, that it is not much greater than that which we have been endeavouring to ascertain. We will, therefore, consider the postulatum as established. It will then follow, that nine parts in ten of the sun's rays are reflected from the upper surface of a common stratum of clouds, or lost in their passage through it. That the reflected rays are very copious, will appear by the resplendent whiteness of small detached clouds, when strongly illuminated by the sun. We can also easily conceive, that a large part of the rays, which enter the clouds, will be absorbed and lost in them, when we consider the infinite number of reflections and refractions they must suffer in their passage. The rays which make their way

through, probably suffer nearly as many reflections and refractions as those which are stopped. It is, therefore, natural to conclude, that their velocity is greatly diminished at the time of their exit from the lower surface of the clouds; for the causes that were able to stop nine-tenths of the rays must necessarily have greatly retarded the rest.

"Now let us suppose a second stratum of clouds, thick and compact, to intervene between the first and the earth, as happened on the memorable 19th of May. The rays that fortunately effected their passage through the first, were not only deprived of a great part of their velocity, but turned out of their direct course, so that they must have struck upon the second very obliquely. By this means a much larger proportion of them than common was reflected from the upper surface of the clouds that composed it. The rest having to penetrate a very thick and compact body of vapors, with a velocity exceedingly diminished, had not a sufficiency of momentum to overcome the resistance they had to encounter from the numerous reflections and refractions they met with, and were consequently lost in their passage. Nor will it appear strange, that, when nine-tenths of the incident rays, while proceeding with their inconceivable native velocity, were lost in passing a common stratum of clouds, the remainder should be so generally lost in such a body of vapor as then opposed their progress, after they had been so fatigued and tamed (if I may borrow the expression) in their struggles to force a passage through the first obstacle. The wonder is much greater, that any of them were able to penetrate. 'T is certain, however, that a small proportion were so fortunate. These were sufficient to render terrestrial objects visible, while their yellow hue thrown upon the foliage and herbage diminished the intensity of their natural green, which is a compound colour, and gave them the resplendent and beautiful tint they exhibited.

"The darkness of the following evening was probably as