Snow is furnished with the power of absorbing and combining with a large portion of oxygen, which gives it its fertilizing property. The snow melting and penetrating into the softened earth communicates to it oxygen, and this oxygen promotes the germination of seeds. The carbon of the earth combining with the oxygen, is converted into carbonic acid, and thereby acquires more solubility; while the water contributes to excite that activity which had been rendered dormant in the roots by the cold. It is this property of carbon which deprives water of the superabundant oxygen that would render it prejudicial to health, and unfit for the purposes of life. Thus what would otherwise be injurious to us is improved by the ground, and gives at the same time power and activity to the mould. How multiplied are those means which infinite wisdom and goodness employ for the preservation of the productions of Nature![88]
Ice at 32° must absorb 140° of caloric before it can become a fluid; or such a quantity as would raise a body of water of equal bulk with itself from 32° to 172°. For instance: “Take any quantity by weight of ice or snow at 32°, and mix it with an equal weight of water heated exactly to 172°. The snow instantly melts, and the temperature of the mixture is still only at thirty-two degrees. Here the water is cooled 140°, while the temperature of the snow is not increased at all; so that 140° of caloric have disappeared. They must have combined with the snow; but they have only melted it, without increasing its temperature. Hence it follows irresistibly that ice, when converted into water, absorbs and combines with 140° of caloric. Water then, after being cooled down to 32°, cannot freeze till it has parted with 140° of caloric; and ice, after being heated to 32°, (which is the exact freezing point), cannot melt till it has absorbed 140° more of caloric. This is the cause of the extreme slowness of these operations. There can be no doubt, then, but water owes its fluidity to its latent caloric, and that its caloric of fluidity is 140°”.[89] And all this arrangement in nature, connected with the operation of these elements, is immediately under the control and direction of the infinitely wise and almighty Creator of the universe. “He sendeth forth his commandment upon earth: his word runneth very swiftly. He giveth snow like wool: he scattereth the hoar-frost like ashes. He casteth forth his ice like morsels: who can stand before his cold? He sendeth out his word, and melteth them: he causeth his wind to blow, and the waters flow.”
Drops of rain, falling through a cold region of the atmosphere, are frozen and converted into hail; and thus the hail is produced by rain. When it begins to fall, it is rain; when it is falling, it is converted into hail; so that it is literally true, that it rains hail. The further a hail-stone falls, the larger it generally is; because, in its descent, meeting with innumerable particles of water, they become attached to it, are also frozen, and thus its bulk is continually increasing till it reaches the earth.[90] A storm of hail fell near Liverpool, in Lancashire, in the year 1795, which greatly damaged the vegetation, broke windows, &c., &c. Many of the stones measured five inches in circumference. Dr. Halley mentions a similar storm of hail in Lancashire, Cheshire, &c., April 29, 1697, that for sixty miles in length, and two miles in breadth, did immense damage, by splitting trees, killing fowls and all small animals, knocking down men and horses, &c., &c. Mezeray, in his History of France, says, that in Italy, in 1510, there was for some time a horrible darkness, thicker than that of night; after which the clouds broke into thunder and lightning, and there fell a shower of hail-stones which destroyed all the beasts, birds, and even fish of the country. It was attended with a strong smell of sulphur, and the stones were of a blueish color, some of them weighing one hundred pounds weight. The Almighty says to Job—“Hast thou seen the treasures of the hail, which I have reserved against the time of trouble, against the day of battle and war.” While God has such artillery at his command, how soon may he desolate a country, or a world![91]
The aqueous fluid is in continual circulation. The constant round which it travels, says Dr. Paley, and by which, (without suffering either adulteration or waste,) it is continually offering itself to the wants of the habitable globe, is much to be admired. From the sea are exhaled, by the heat of the sun, into the air, those vapors which are there condensed into clouds: these clouds are dissolved into rain and dew, or into snow and hail, which are but rain congealed, by the coldness of the air, and descend in showers, which, penetrating into the crevices of the hills, supply the springs: which springs flow in little streams into the valleys; and there uniting, become rivers, which rivers, in return, feed the ocean. So there is an incessant circulation of the same fluid; and not one drop probably more or less now than there was at the creation. A particle of water takes its departure from the surface of the sea, in order to discharge certain important offices to the earth: and, having executed the service which was assigned to it, returns to the bosom which it left.[92] Thus, as one of the greatest of naturalists says, “All the rivers run into the sea; yet the sea is not full: unto the place from whence the rivers come, thither they return again.”
Water, when taken up by the atmosphere, is not in an aqueous state, but is converted into vapor by the efficiency of heat, and then combines with more than five times the quantity of caloric than is required to bring ice-cold water to a boiling heat, and occupies a space 800 times greater than it does when in the form of water. A large portion of the matter of heat combining chemically with water, renders it specifically lighter; which is the cause of its rising and mixing with the atmosphere. The waters on the face of the earth would be dissipated in vapor by a small degree of heat, if we had no atmosphere. Under the pressure of the atmosphere water boils at 212°, but in vacuo it boils when heated only to 67°. On the contrary, if additional pressure be given to water by a Papin’s digester, it may be heated to 400°, without producing ebullition. However long we boil a fluid, in an open vessel, we cannot make it in the smallest degree hotter than the boiling point.[93] When arrived at this point, the vapor absorbs the heat, and carries it off as fast as it is generated. When water is received into the atmosphere, if the air be warm, it becomes so far changed by its union with the matter of heat as to be perfectly invisible. In this state it occupies a space 1,400 times greater than its ordinary liquid state.
After vapor has remained some time in the atmosphere, it becomes in a measure condensed; and the particles of water of which it is composed unite, and form hollow vesicles, which accumulate together and produce clouds. How this is effected, those who have attentively considered the subject are not agreed. Dr. Thomson, after well investigating the matter, concludes, from all the facts, that “the formation of clouds and rain cannot be accounted for by a single principle with which we are acquainted.” It is, however, says Mr. Parkes, probable that electricity alone is the primary cause. Saussure conjectures that it is the electrical fluid which surrounds these vesicles, and prevents them from dissolving in the air. And the idea of the formation of clouds by the agency of electricity was mentioned by Volta, and also by Dr. Franklin.
[It is allowed by all, that clouds are formed by the aqueous vapors which are held suspended, or in solution, by the atmosphere. It is not a settled question, whether the air holds these vapors in solution, or merely suspended; and thus, keeping the particles asunder, prevents their condensation.
This aqueous vapor is invisible when perfectly in union with the air. When it begins to separate from the air, it becomes visible by condensation, in the form of clouds, mists, and fogs. When it is perfectly separated and sufficiently condensed it becomes rain, and when the temperature is sufficiently low to freeze the condensed drops, they become snow, or hail.
The above process is quite intelligible, but the agent of this condensation is, perhaps, inexplicable. It is impossible to solve all the phenomena of the formation of clouds, by supposing the vapors condensed by a reduction of temperature, produced by the warmer volumes of clouds rising into the regions of colder ones. For we know the natural tendency of the warmer strata of air, from the neighborhood of the earth, is to rise, with its watery particles, to colder regions. Hence there would be a constant condensation, which would seem to require a constant deposition of rain, or mist; or, at least, a constant accumulation of clouds.
Again: On this theory, the nights would be cloudy and rainy: as the vapors raised during the day would be condensed by the superior coldness of the night succeeding. Moreover, it is well known that great rains fall in very warm weather, and when a rise of temperature is observed.
These, and other considerations, have induced many persons to have recourse to electricity to solve this difficult question, and various observations seem to countenance the idea that it may be the remote agent of the formation of clouds, by producing a sudden rarefaction of the air, which would, of course, produce a sudden reduction of temperature; the consequence of which would be a rapid condensation of the watery particles in combination with the air. This condensation would form clouds, and if sufficiently rapid and extensive, a fall of rain would ensue.
This supposition is much strengthened by a fact of common observation, viz: when clouds are impending over us, but no rain falling, a sudden shower comes down instantly upon a flash of lightning. In this case it is so obvious that the lightning had an immediate agency, that none can doubt, who ever observed the phenomenon.
The electrified state of clouds, fogs, and mists, is considered strong proof in favor of this theory. Clouds are almost always highly charged with electricity, and sometimes so highly charged as to become luminous, and very destructive.
On the 11th of August, 1772, about midnight, a bright cloud was observed covering a mountain in the district of Cheribon, in the island of Java, at the same time several reports were heard like those of a gun. The people who dwelt upon the upper parts of the mountain not being able to fly fast enough, a great part of the cloud, almost three leagues in circumference, detached itself under them, and was seen at a distance rising and falling like the waves of the sea, and emitting globes of fire so luminous, that the night became as clear as day. The effects of it were astonishing; every thing was destroyed for seven leagues round; the houses were demolished; plantations were buried in the earth, and 2,140 people lost their lives. Ency. Brit. Article, Clouds.
In another case, October 29th, 1757, in the island of Malta, a little after midnight, there was seen to the South west of the city Melita, a great black cloud, which, as it approached, changed its color, till at last it became like a flame of fire mixed with smoke. A dreadful noise was heard on its approach, which alarmed the whole city. It passed over the port, and came first on an English ship, which in an instant was torn to pieces, and nothing left but the hulk; part of the masts, sails, and cordage were carried to a considerable distance along with the cloud. The small craft were sunk instantly. It demolished a part of the city, and passed over to Sicily, but did no injury there as it was previously exhausted. Several hundred were killed. Ency. Brit. Article, Cloud.]
The principle of evaporation is the primary cause of all rain, mist, dew, &c. The ocean loses many millions of gallons of water hourly by evaporation. The Mediterranean alone is said to lose more by it, than it receives from the Nile, the Tiber, the Rhone, the Po, and all the other rivers that fall into it. When Dr. Halley made his celestial observations upon the tops of the mountains at St. Helena, he found that the quantity of vapor which fell there (even when the sky was clear) was so great, that his observations were thereby much impeded: his glasses were so covered with water through the condensation of the vapors, that he was obliged to wipe them every ten minutes. In order to determine, with some degree of accuracy, how much water would be raised in vapor in any space of time, he took a vessel of water salted to the same degree with that of sea-water, in which he placed a thermometer, and by means of a pan of coals brought the water to the same degree of heat as would be produced by the sun in summer: he then affixed the vessel of water with the thermometer in it, to one end of a pair of scales, and exactly counterpoised it with weights on the other. Then, at the end of two hours, he found by the alteration in the weight of the vessel, that a sixtieth part of an inch in the depth of the water was gone off in vapor; and therefore, in twelve hours, one-tenth of an inch would have gone off. From this experiment the Doctor calculates (in as accurate a manner as the subject will admit of) the quantity of water raised by evaporation from the Mediterranean Sea, to be at least five thousand two hundred and eighty millions of tons of water in a day; and from the river Thames twenty millions three hundred thousand tons per day, on the average.
This water is conveyed by the winds to every part of the continents: these it fertilizes in the form of rain, and afterwards supplies the rivers, which flow again into the sea. In our climate, evaporation is found to be about four times as much from the vernal to the autumnal equinox, as from the autumnal to the vernal. Heat facilitates all solutions; and the greater the difference between the temperature of the air and the evaporating surface, the greater will be the evaporation. Bishop Watson found that, even when there had been no rain for a considerable time, and the earth had been dried by the parching heat of summer, an acre of ground dispersed into the air above 1,600 gallons of water in the space of twelve hours of a summer’s day. A little reflection would convince any one of the importance of the principle of evaporation. Innumerable instances of its use might be adduced; suffice to add, that without it neither grass nor corn could be sufficiently void of moisture to lay up for use. Our clothes when washed could not be dried; neither could a variety of the most common operations, which conduce much to our comfort and convenience, be performed without it.
It is evident that water exists in the atmosphere in abundance, even in the driest seasons, and under the clearest sky. By the experiments of Saussure, it appears, that a cubic foot of atmospheric air will hold eleven grains of water in solution. From this property of the air we derive many advantages. It has a tendency to preserve every thing on the face of the earth in a proper degree of moisture. It appears, from the experiments of some aëronauts, that the air is much drier in the higher regions than it is near the surface of the earth.