FREEZING
, or Congelation, the fixing of a fluid body into a firm or solid mass by the action of cold: in which sense the term is applied to water when it freezes into ice; to metals when they resume their solid form after being melted by heat; or to glass, wax, pitch, tallow, &c, when they harden again after having been rendered fluid by heat. But it differs from crystallization, which is rather a separation of the particles of a solid from a fluid in which it had been dissolved more by the moisture than the action of heat.
The process of congelation is always attended with the emission of heat, as is found by experiments on the freezing of water, wax, spermaceti, &c; for in such cases it is always found that a thermometer dipt into the fluid mass, keeps continually descending as this cools, till it arrive at a certain point, being the point of freezing, which is peculiar to each fluid, where it is rather stationary, and then rises for a little, while the congelation goes on. But by what means it is that fluid bodies should thus be rendered solid by cold, or fluid by heat, or what is introduced into the bodies by either of those principles, are matters the learned have never yet been able to discover, or to satisfy them- selves upon. The following phenomena however are usually observed.
Water, and some other fluids, suddenly dilate and expand in the act of Freezing, so as to occupy a greater space in the form of ice than before, in consequence of which it is that ice is specifically lighter than the same fluid, and floats in it. And the degree of expansion of water, in the state of ice, is by some authors computed at about 1/10 of its volume. Oil however is an exception to this property, and quicksilver too, which shrinks and contracts still more after Freezing. Mr. Boyle relates several experiments of vessels made of metal, very thick and strong; in which, when filled with water, close stopped, and exposed to the cold, the water being expanded in Freezing, and not sinding either room or vent, burst the vessels. A strong barrel of a gun, with water in it close stopped and frozen, was rent the whole length. Huygens, to try the force with which it expands, filled a cannon with it, whose sides were an inch thick, and then closed up the mouth and vent, so that none could escape; the whole being exposed to a strong Freezing air, the water froze in about 12 hours, and burst the piece in two places. Mathematicians have computed the force of the ice upon this occasion; and they say, that such a force would raise a weight of 27720 pounds. Lastly, Major Edward Williams, of the Royal Artillery, made many experiments on the force of it, at Quebec, in the years 1784 and 1785. He filled all sizes of iron bomb-shells with water, then plugged the fuze hole close up, and exposed them to the strong Freezing air of the winter in that climate; sometimes driving in the iron plugs as hard as possible with a sledge hammer; and yet they were always thrown out by the sudden expansion of the water in the act of Freezing, like a ball shot by gunpowder, sometimes to the distance of between 400 and 500 feet, though they weighed near 3 pounds; and when the plugs were screwed in, or furnished with hooks or barbs, to lay hold of the inside of the shell by, so that they could not possibly be forced out, in this case the shell was always split in two, though the thickness of the metal of the shell was about an inch and three quarters. It is farther remarkable, that through the circular crack, round about the shells, where they burst, there stood out a thin film or sheet of ice, like a fin; and in the cases when the plugs were projected by Freezing water, there suddenly issued out from the fuze-hole, a bolt of ice, of the same diameter, and stood over it to the height sometimes of 8 inches and a half. And hence we need not be surprised at the effects of ice in destroying the substance of vegetables and trees, and even splitting rocks, when the frost is carried to excess.
It is also observed that water loses of its weight by Freezing, being found lighter after thawing again, than before it was frozen. And indeed it evaporates almost as fast when frozen, as when it is fluid.
It is said too that water does not freeze in vacuo; requiring for that purpose the presence and contiguity of the air. But this circumstance is liable to some doubt, and it may be suspected that the degree of cold has not been carried far enough in these instances; as it is found that mercury in thermometers has even been| frozen, though it requires a vastly greater degree of cold to freeze mercury, than water.
That water which has been boiled freezes more readily than that which has not been boiled; and that a slight disturbance of the fluid disposes it to freeze more speedily; having sometimes been cooled several degrees below the Freezing point, without congealing when kept quite still, but suddenly freezing into ice on the least motion or disturbance.
That the water, being covered over with a surface of oil of olives, does not freeze so readily as without it; and that nut oil absolutely preserves it under a strong frost, when olive oil would not.
That rectified spirit of wine, nut oil, and oil of turpentine, seldom freeze.
That the surface of the water, in Freezing, appears all wrinkled; the wrinkles being sometimes in parallel lines, and sometimes like rays, proceeding from a centre to the circumference.
Freezing Mixture, a preparation for the artificial congelation of water, and other fluids.
According to Mr. Boyle, all kinds of salts, whether alkaline or acid; and even all spirits, as spirit of wine, &c; as also sugar, and saccharum saturni, mixed with snow, are capable of Freezing most fluids; and the same effect is produced, in a very high degree, by a mixture of oil of vitriol, or spirit of nitre, with snow.
M. Homberg remarks the same of equal quantities of corrosive sublimate, and sal ammoniac, with four times the quantity of distilled vinegar.
Boerhaave gives a method of producing artisicial frost without either snow or ice: we must have for this purpose, at any season of the year, the coldest water that can be procured; this is to be mixed with a proper quantity of any salt (sal ammoniac will answer the intention best), at the rate of about 3 ounces to a quart of water. Another quart of water must be prepared in the same manner with the first; the salt, by being dissolved in each, will make the water much colder than it was before. The two quarts are then to be mixed together, and this will make them colder still. Two quarts more of water prepared and mixed in the same manner are to be mixed with these, which will increase the cold to a much higher degree in all. The whole of this operation is to be carried on in a cold cellar; and a glass of common water is then to be placed in the vessel of the fluid thus artificially cooled, and it will be turned into ice in the space of 12 hours.
There is also a method of making artisicial ice by means of snow, without any kind of salt. For this purpose fill a small pewter dish with water, and upon that set a common pewter plate filled, but not heaped, with snow. Bring this simple apparatus near the fire, and stir the snow in the plate: the snow will dissolve, and the ice will be formed on the back of the plate, which was set in the dish of water.
Mr. Reaumur tried the effect of several salts, and examined the various degrees of cold by an ice thermometer, which being placed in the fluid to be frozen, shewed very exactly the degree of cold by the descent of the spirit.
Nitre, or saltpetre, usually passes for a salt that may be very serviceable in these artisicial congelations; but the experiments of this gentleman prove that this opi- nion is erroneous. The most perfectly resined saltpetre employed in the operation sunk the spirit in the thermometer only 3 degrees and a half below the fixed point. Less refined nitre sunk the thermometer lower, and gave a greater degree of cold; owing to the common or sea-salt that it contains when less pure, which has a greater effect than the pure saltpetre itself.
Two parts of common salt being mixed with three parts of powdered ice in very hot weather, the spirit in the thermometer immediately descended 15 degrees, which is half a degree lower than it would have descended in the severest cold of our winters. Mr. Reaumur then tried the salts all round, determining with great regularity and exactness, what was the degree of cold occasioned by each in a given dose. Among the neutral salts, none produced a greater degree of cold than the common sea salt. Among the alkalies, sal ammoniac sunk the thermometer only to 13 degrees. Pot-ashes sunk it just as low as well refined saltpetre.
For the common uses of the table, the ice is not required to be very hard, or such as is produced by long continuance of violent cold: it is rather desired to be like snow. Saltpetre, which is no very powerful freezer, is therefore more fit for the purpose than a more potent salt. It is not necessary that the congelation should be very suddenly made; but that it may retain its sorm as long as may be, when made, is of great importance.
If it be desired to have ices very hard and sirm, and very suddenly prepared, then sea salt is of all others most to be chosen for the operation. The ices thus made will be very hard, but they will soon run. Pot-ashes afford an ice of about the hardness that is usually required. This forms indeed very slowly, but then it will preserve a long time. And common wood ashes will perform the business very nearly in the same manner as the pot-ashes; but for this purpose, the wood which is burnt, ought to be fresh.
The strong acid spirits of the neutral salts act much more powerfully in these congelations than the salts themselves, or indeed than any simple salt can do. Thus, spirit of nitre mixed with twice its quantity of powdered ice, immediately sinks the spirit in the thermometer to 19 degrees, or 4 degrees more than that obtained by means of sea salt, the most powerful of all the salts in making artisicial cold. A much greater degree of cold may be given to this mixture, by piling it round with more ice mixed with sea salt. This gives a redoubled cold, and sinks the thermometer to 24 degrees. If this whole matter be covered with a fresh mixture of spirit of nitre and ice, a still greater degree of cold is produced, and so on; the cold being by this method of fresh additions to be increased almost without bounds: but it is to be observed, that every addition gives a smaller increase than the former.
It is very remarkable in the acid spirits, that though sea salt is so much more powerful than nitre in substance in producing cold, yet the spirit of nitre is much stronger than that of sea salt; and another not less wonderful phenomenon is, that spirit of wine, which is little else than liquid fire, has as powerful an effect in congelations, or very nearly so, as the spirit of nitre itself.| The several liquid substances which produce cold, in the same manner as the dry salts on being mixed with ice, are much more speedy in their action than the salts: because they immediately and much more intimately come into contact with the particles of the ice, than the salts can. Of this nature are spirit of nitre, spirit of wine, &c. To produce the expected degree of cold, it is always necessary that the ice and the added matter, whatever it be, should both run together, and, intimately uniting, form one clear fluid. It is hence that no new cold is produced with oil, which, though it melts the ice, yet cannot mix itself into a homogeneous liquid with it, but must always remain floating on the surface of the water that is produced by the melting of the ice. Mem. Acad. Scienc. Par. 1734.
It has been discovered, that sluids standing in a current of air, grow by this means much colder than before. Fahrenheit had long since observed, that a pond, which stands quite calm, often acquires a degree of cold much beyond what is sufficient for Freezing, and yet no congelation ensued: but if a slight breath of air happens in such a case to brush over the surface of the water, it stiffens the whole in an instant. It has also been discovered, that all substances grow colder by the evaporation of the fluids which they contain, or with which they are mixed. If both these methods therefore be practised upon the same body at the same time, they will increase the cold to almost any degree of intenseness we please.
But the most extraordinary instances of artificial Freezing, have since been made in Russia, at Hudson's bay, and other parts, by which quicksilver was frozen into a solid mass of metal. And the same thing had before happened from the natural cold of the atmosphere alone, in Siberia. In the winter of 1733, Professor Gmelin, with two other gentleman of the Russian Academy, were sent by Anne Ivanouna, the new empress, to explore and describe the different parts of her Asiatic dominions, with the communication of Asia and America. In the winter of 1734-5, Mr. Gmelin being at Yeneseisk in 58° 30′ north lat. and 92° long. east from Greenwich, first observed such a descent of the mercury, as must have been attended with congelation, being far below its Freezing point, now fixed at - 40 of Fahrenheit's thermometer. “ Here, says he, we first experienced the truth of what various travellers have related with respect to the extreme cold of Siberia; for, about the middle of December, such severe weather set in, as we were sure had never been known in our time at Petersburg. The air seemed as if it were frozen, with the appearance of a fog, which did not suffer the smoke to ascend as it issued from the chimneys. Birds fell down out of the air as dead, and froze immediately, unless they were brought into a warm room. Whenever the door was opened, a fog suddenly formed round it. During the day, short as it was, parhelia and haloes round the sun were frequently seen; and in the night mock moons, and haloes about the moon. Finally, our thermometer, not subject to the same deception as the senses, left us no doubt of the excessive cold; for the quicksilver in it was reduced, on the 5th of January, old style, to - 120° of Fahrenheit's scale, lower than it had ever been observed in na- ture.”
The next instance of congelation happened at Yakutsk, in 62° north lat. and 150° east longitude. The weather here was unusually mild for the climate, yet the thermometer fell to - 72°; and one person informed the professor by a note, that the mercury in his barometer was frozen. He hastened immediately to his house to behold such a surprising phenomenon; but though he was witness to the fact, observing that the mercury did not continue in one column, but was divided in different places as into little cylinders, which appeared frozen, yet the prejudice he had entertained against the possibility of the congelation, would not allow him to believe it.
Another set of observations, in the course of which the mercury must frequently have been cougealed, were made by professor Gmelin at Kirenga fort, in 57 1/2 north lat., and 108 east long.; his thermometer, at different times, standing at - 108, - 86, - 100, - 113, and many other intermediate degrees; in the course of the winter of 1737-8. On the 27th of November, after the thermometer had been standing for two days at - 46°, he found it sunk at noon to - 108. Suspecting some mistake, after he had noted down the observation, he instantly ran back, and found it at - 102; but ascending with such rapidity, that in the space of half an hour it had risen to - 19°. This phenomenon, which appeared so surprising, doubtless depended on the expansion of the mercury frozen in the bulb of the thermometer, and which now melting, forced upwards the small thread in the stem. And similar appearances were observed on other days afterwards, when the thread of quicksilver in the thermometer was separated about 6 degrees.
A second instance where a natural congelation of mercury has certainly been observed, is recorded in the transactions of the Royal Academy of Sciences at Stockholm, as made by Mr. Andrew Hellant. The weather, in January 1760, was remarkably cold in Lapland; so that on the 5th of that month, the thermometers fell to - 76, - 128, or lower; on the 23d and following days they fell to - 58, - 79, - 92, and below - 238 entirely into the ball. This was observed at four different places in Lapland, situated between the 65th and 78th degrees of north lat. and the 21st and 28th degree of east longitude.
But the congelation of quicksilver, by an artificial Freezing mixture, was sirst observed, and put beyond doubt, by Mr. Joseph Adam Braun, professor of philosophy at Petersburg. This gentleman wishing to try how many degrees of cold he could produce, availed himself of a good opportunity which offered for that purpose on the 14th of December 1759, when the mercury in the thermometer stood in the natural cold at - 34, which it is now known is only 5 or 6 degrees above its point of congelation. Assisting this natural cold therefore with a mixture prepared of aquafortis and pounded ice, his thermometer was sunk to - 69. Part of the quicksilver must now have been really congealed, but unexpected by him, and he only thought of pursuing his object of producing still greater degrees of cold; and having expended all his pounded ice, he was obliged to use snow instead of it. With this fresh mixture the mercury sunk to - 100, - 240, and - 350°. Taking the thermometer out, he found it| whole, but the quicksilver fixed, and it continued so for 12 minutes. On repeating the experiment, with another thermometer which had been graduated no lower than - 220, all the mercury sunk into the ball, and became solid as before, and did not re-ascend till after a still longer interval of time. Mr. Braun now suspected that the quicksilver was really frozen, and prepared for making a decisive experiment. This was accomplished on the 25th of the same month, and the bulb of the thermometer broken as soon as the metal was congealed; when it appeared that the mcrcuty was changed into a solid and shining metallic mass, which flatted and extended under the strokes of a pestle, being rather less hard than lead, and yielding a dull sound like that metal. Mr. Æpinus made similar experiments at the same time, employing as well thermometers as tubes of a larger bore; in which last he remarked, that the quicksilver fell sensibly on being frozen, assuming a concave surface, and likewise that the congealed pieces sunk in fluid mercury: also, in their farther experiments, they invariably found that the mercury sunk lower when the whole of it was congealed, than if any part of it remained fluid: all shewing that, contrary to water, mercury contracted in Freezing. It was farther observed, that the mercury when congealed looked like the most polished silver, and when beaten flat, it was easily cut with a penknife, like soft thin sheet lead.
The fact being thus established, and fluidity no longer to be considered as an essential property of quicksilver, Mr. Braun communicated an account of his experiments to the Petersburg academy, on the 6th of September 1760; of which a large extract was inserted in the Philos. Trans. vol. 52, pa. 156. He afterwards declared that he never suffered a winter to pass without repeating the experiment of Freezing quicksilver, and never failed of success when the natural cold was of a sufficient strength for the purpose; and this degree of natural cold he supposes at - 10 of Fahrenheit; though some commencement of the congelation might be perceived when the temperature of the air was as high as + 2.
The results of all his experiments were, that with the abovementioned frigorific mixtures, and once with rectified spirits and snow, when the natural cold was at - 28°, he congealed the quicksilver, and discovered that it is a real metal that melts with a very sinall degree of heat. However, not perceiving the necessary consequence of its great contraction in Freezing, he always confounded its point of congelation with that of its greatest contraction in Freezing, and thus marked the former a great deal too low.
In the process of his observations, Mr. Braun found that double aquafortis was more effectual than spirit of nitre; but with this simple spirit, which seldom brings the mercury lower than - 148, this metal may be frozen in the following manner: Six glasses being filled with snow as usual, and the thermometer put in one of them, the spirit of nitre was poured upon it; when the mercury would fall no lower in this, the thermometer was removed to the second, and so on to the third and fourth, in which fourth immersion the mercury was congealed.
Mr. Æpinus gives the following direction for using the fuming spirit of nitre: Take some of this spirit, cooled as much as possible, and put it into a wine glass till it be about half full, filling it up with snow, and stirring them till the mixture become of the consistence of pap; by which means you obtain, almost in an instant, the necessary degree of cold for the Freezing of quicksilver.
It is remarked by Mr. Braun, that by the mixture of snow and spirit of nitre, which froze the mercury, he never was able to bring thermometers, filled with the most highly rectified spirit of wine, lower than - 148: so that the cold which will freeze mercury, will not freeze spirit of wine; and therefore spirit thermometers are the most sit to determine the degree of coldness in frigorific mixtures, till we can construct solid metallic thermometers with sufficient accuracy. Mr. Braun tried the effects of different Fluids in his frigorific mixtures: he always found that Glauber's spirit of nitre and double aquafortis were the most powerful; and from a number of experiments made when the temperature of the air was between 21 and 28 of Fahrenheit, he concludes, that spirit of salt pounded upon snow increased the natural cold 36°; spirit of sal ammoniac, 12; oil of vitriol, 42; Glauber's spirit of nitre, 70; aquafortis, 48; simple spirit of nitre, 36; dulcified spirit of vitriol, 24; Hoffman's anodyne liquor, 38; spirit of hartshorn, 12; spirit of sulphur, 12; spirit of wine rectified, 24; camphorated spirit, 18; French brandy, 14; and several kinds of wine increased the natural cold to 7, 8, or 9 degrees.
The most remarkable congelation of mercury, by natural cold, that has ever been observed, was that related by Dr. Peter Simon Pallas, who had been sent by the empress of Russia, with some other gentlemen, on an expedition similar to that of Mr. Gmelin. Being at Krasnoyarsk in the year 1772, in north lat. 56° 30′, and east long. 93°, he had an opportunity of observing the phenomenon we speak of. On the 6th and 7th of December that year, says he, there happened the greated cold I have ever experienced in Siberia: the air was calm at the time, and seemingly thickened; so that, though the sky was in other respects clear, the sun appeared as through a fog. I had only one small thermometer left, in which the scale went no lower than - 7°; and on the 6th in the morning, I remarked that the quicksilver in it sunk into the ball, except some short columns which stuck fast in the tube. When the ball of the thermometer, as it hung in the open air, was touched with the finger, the quicksilver rose; and it could plainly be seen that the solid columns stuck and resisted a good while, and were at length pushed upward with a sort of violence. He also placed upon the gallery, on the north side of his house, some quicksilver in an open bowl. Within an hour he found the edges and surface of it frozen solid; and some minutes afterward the whole was condensed by the natural cold into a soft mass very much like tin. While the inner part was still fluid, the frozen surface exhibited a great variety of branched wrinkles; but in general it remained pretty smooth in Freezing. The congealed mercury was more flexible than lead; but on being bent short, it was found more brittle than tin; and when hammered out thin, it seemed somewhat granulated. When the hammer was not perfectly cooled, the| quicksilver melted away under it in drops; and the same thing happened when the metal was touched with the finger, by which also the finger was immediately benumbed. When the frozen mass was broken to pieces in the cold, the fragments adhered to each other and to the bowl in which they lay. In the warm room it thawed on its surface gradually, by drops, like wax on the fire, and did not melt all at once. Although the frost seemed to abate a little towards night, yet the congealed quicksilver remained unaltered, and the experiment with the thermometer could still be repeated. On the 7th of December he had an opportunity of making the same observations all day; but some hours after sunset, a northwest wind sprung up, which raised the thermometer to - 46°, when the mass of quicksilver began to melt.
The experiments of Mr. Braun were successfully repeated at Gottingen, in 1774, by Mr. John Frederick Blumenbach; being encouraged to this attempt by the exceffive cold of the winter that year, especially the night of January the 11th, when he made the experiment, the thermometer standing at - 10 in the open air. Mr. Blumenbach at 5 in the evening, put 3 drachms of quicksilver into a small sugar glass, and covered it with a mixture of snow and Egyptian sal ammoniac, setting the glass out in the air upon a mixture also of sal ammoniac. At one the next morning, the mercury was found frozen quite solid, and hard to the glass; and did not melt again till 7 or 8 the next morning. The colour of the frozen mercury was a dull pale white with a blueish cast, like zinc, very different from the natural appearance of quicksilver.
In the year 1775, by similar means, quicksilver was twice frozen by Mr. Hutchins, governor of Albany fort, in Hudson's bay, viz, in the months of January and February of that year. And the same was done on the 28th of January 1776, by Dr. Lambert Bicker, secretary of Rotterdam. The temperature of the atmosphere was then at + 2°; and the lowest it could reduce the thermometer by artificial cold, was - 94; when, on breaking the glass, the mercury was found frozen.
In the beginning of the year 1780 M. Von Elterlein of Vytegra, a town of Russia, in lat. 61° north, and long. 36° east, froze quicksilver by natural cold. On the 4th of January 1780, the cold being increased to - 34 that evening at Vytegra, he exposed to the open air 3 ounces of very pure quicksilver in a china teacup, covered with paper pierced full of holes. Next day, at 8 in the morning, he found it solid, and looking like a piece of cast lead, with a considerable depression in the middle. On attempting to loosen it in the cup, his knife raised shavings from it as if it had been lead, which remained sticking up; and at length the metal separated from the bottom of the cup in one mass. He then took it in his hand to try if it would bend: it was stiff like glue, and broke into two pieces; but his fingers immediately lost all feeling, and could scarcely be restored in an hour and a half by rubbing with snow. At 8 o'clock the thermometer stood at - 57; but half after 9 it was risen to - 40; and then the two pieces of mercury which lay in the cup had lost so much of their hardness, that they could no longer be broken, or cut into shavings, but resembled a thick amalgam, which, though it became fluid when pressed by the fingers, immediately afterwards resumed the consistence of pap. With the thermometer at - 39, the quicksilver became fluid. The cold was never less on the 5th than - 28, and by 9 in the evening it had increased again to - 33. This experiment seems to fix the Freezing point of mercury at - 40 of Fahrenheit's thermometer, or 40 below 0; which is 72° below the Freezing point of water.
In the winter of 1781 and 82, Mr. Hutchins resumed the subject of Freezing quicksilver by artificial cold, with such success, that from his experiments and those of M. Von Elterlein, last mentioned, the Freezing point of mercury is now almost as well fettled, viz at - 40, as that of water is at + 32. Other philosophers indeed had not been altogether inattentive to this subject. Professor Braun himself had taken great pains to investigate it; but for want of a proper attention to the difference between the contraction of the fluid mercury by cold, and that of the congealing metal by Freezing, he could not determine any thing certain concerning it.
An instance of the natural congelation of quicksilver also occurred in Jemptland, one of the provinces of Sweden, on the 1st of January 1782; and lastly, on the 26th of the same month, Mr. Hutchins observed the same effect of the cold at Hudson's bay; when he found that at the point of its Freezing a mercurial thermometer stood at - 40, and a spirit thermometer at - 30.
On this subject, see the Philos. Trans. vol. 51, pa. 672; vol. 52, pa. 156; vol. 66, pa. 174; vol. 73, pa. 303 and 325; vol. 76, pa. 241; vol. 77, pa. 285; vol. 78, pa. 43; and several others, particularly vol. 79, pa. 199, &c, being experiments on the congelation of quicksilver in England, by Mr. Richard Walker, where he proves that mercury may be frozen not only in England in summer, but even in the hottest climate, at any season of the year, and without the use of ice or snow.
Freezing Point, denotes the point or degree of cold, shewn by a mercurial thermometer, at which certain sluids begin to freeze, or, when frozen, at which they begin to thaw again. On Fahrenheit's thermometer, this point is at + 32 for water, and at - 40 for quicksilver, these fluids freezing at those two points respectively. It would also be well if the Freezing points for other fluids were ascertained, and the whole arranged in a table.
Freezing Rain, or Raining Ice, a very uncommon kind of shower which sometimes falls, particularly one in December 1672, in the west of England: of which some accounts are given in the Philos. Trans. number 90.
This rain, as soon as it touched any thing above ground, as a bough, or the like, immediately settled into ice; and by enlarging and multiplying the icicles, it broke all down with its weight. The rain that fell on the snow, immediately froze into ice, without sinking in the snow at all.
It made an amazing destruction of trees, beyond any thing in all history. “ Had it concluded with some gust of wind, says a gentleman on the spot, it might have been of terrible consequence. Having weighed| the sprig of an ash tree, the wood of which was just three quarters of a pound, the ice upon it amounted to 16 pounds. Some were frighted with the noise in the air; till they discerned it was the clatter of icy boughs dashed against each other.” Dr. Beale observes, that there was no considerable frost perceived on the ground during the whole; from which he concludes, that a frost may be very fierce and dangerous on the tops of some hills, while in other places it keeps at some feet above the ground; and may wander about very furious in some places, and be remiss in others not far off. This rain was followed by glowing heats, and a wonderful forwardness of vegetation.
