Honey-wine is said to be excellent; and Dzierzon—one of the most famous German writers on scientific bee-keeping—tells us that it is often manufactured by peasants in Eastern Europe. It is made as follows: Twenty-five pounds of honey are mixed with four and a half gallons of water in a bright copper boiler, the mixture being gently boiled and constantly skimmed during half an hour. Three pounds of finely powdered chalk are then gradually added, under constant stirring. The tough scum which rises to the surface is skimmed off, and when no more rises, the liquid is poured into a wooden vessel, where it is allowed to settle. The liquid is then carefully decanted into the cleaned kettle, mixed with six pounds of finely powdered and recently burned charcoal, and raised to boiling. It is now once more poured into the wooden vessel, allowed to cool, and then filtered through felt or flannel. It should be stated that the chalk is added to neutralise free acid, while the charcoal removes the waxy taste. The filtered liquor is then transferred to the boiler, mixed with the white of twenty-five eggs, and raised to boiling, when the coagulated albumen will have clarified the liquid. After having kept the liquid at a gentle boil for one hour longer, it is allowed to cool, and is then poured into a cask, which must not be quite full, and the bung-hole covered with a piece of clean linen. In this condition it is allowed to remain until fermentation has been completed. When it is perfectly clear, the liquid is drawn off into bottles. We are told by Dzierzon that this wine, if properly prepared, resembles the best brands of Madeira, and is a truly royal beverage. It keeps for any length of time, provided the bottles are stored in a cool cellar.
A NEW THEORY OF DEW.
The explanation of the formation of dew and hoar-frost which Dr Wells published about seventy years ago, has been almost universally accepted as satisfactory ever since. Shortly stated, Dr Wells’ ‘Theory of Dew’ is as follows: Air always contains a certain amount of moisture in the form of invisible vapour. The hotter the air is, the more vapour will it contain. Thus, during a warm day, a good deal of moisture passes into the air; and when the temperature falls in the evening, some of it is deposited as a fine mist. But even when this mist does not appear, dew is formed. As soon as the sun is down, especially if it is a clear evening, the grass, trees, shrubs, and even the soil itself rapidly get cooled by radiating into space the heat which they contain. These cooled bodies in turn cool the warm air above them, and this causes it to deposit more or less of its moisture, which appears either as a film or in minute drops of dew. The points of the grass, small twigs, and all other good radiating surfaces are cooled the most; and accordingly we find the dewdrops most abundant on these bodies; whilst on metal or hard stone surfaces, which are poor radiators, we seldom or never find any dew. A clear, cloudless sky, which promotes radiation, is always favourable to the formation of dew; but on cloudy nights, little is formed, because the clouds return the heat radiated from the earth.
Hoar-frost is only dew deposited on bodies cooled below the freezing-point. It is formed in winter when the temperature of the air during the day is only a little over this point. At night, the grass and ground are soon cooled below thirty-two degrees Fahrenheit, and what moisture is deposited appears as minute ice-crystals or hoar-frost.
Many experiments can be cited which tend to strengthen and confirm this explanation. Thus, every one is familiar with the fact of glass bottles, mirrors, &c., being covered with moisture on being brought into a warm room. The same thing happens with a cold cabbage leaf, or with a bundle of vegetables or a bunch of flowers. On a cold night, the windows of a warm room soon get dimmed. Still more striking is a phenomenon which frequently occurs in countries where the temperature is much below the freezing-point in winter. The houses are well heated, and if a number of people are together, as in a ballroom, the air soon becomes moisture-laden. If the ventilation is not over-good, it may happen that a door or window will be opened. With the rush of cold air from without, the merry-makers are often alarmed by being suddenly covered with hoar-frost, or sometimes even a shower of snow. This does not come from the outside, as it occurs most readily on cold, clear, starlit nights. It is the moisture of the air of the room suddenly cooled below freezing-point that appears as snow or hoar-frost. Many similar experiments may be noticed, all of which are satisfactorily accounted for on Dr Wells’ theory.
Yet, within the last few months, Mr Aitken, in a communication to the Royal Society of Edinburgh, has brought forward many observations, and the results of numerous experiments, which appear to prove that Dr Wells’ theory of dew is not, after all, correct.
The essential difference between the old and the new theories is as to the source of the moisture which forms the dew. Instead of being condensed from the air above by the cooled vegetation, Mr Aitken maintains that it comes from the ground. The author of the original theory admitted that some of the dew might come from below, but affirmed that it must be an exceedingly small proportion. Mr Aitken’s experiments, on the contrary, seem to prove that most if not the whole comes from the ground.
It is quite clear that the grass and soil do get rapidly cooled on dewy nights; but if they are below the temperature of the air above, the ground just under the surface is much warmer. Thermometers placed on the surface of grass were often found ten to eighteen degrees lower than those placed under the surface among the stems. In such circumstances, vapour must be rising from the soil, and part of it will condense on the grass, which has been cooled by radiation. By carefully weighing small squares of turf cut from a lawn before and after the appearance of dew on them, it was always found that they lost weight. If the dew had condensed out of the surrounding air, the turf would have gained in weight by the amount of dew deposited. It was thus clear that vapour was rising from the ground, only part of which was condensed on the grass, the remainder passing into the air.
Another experiment, pointing to the same conclusion, was made by inverting thin trays over the grass. On dewy nights these trays were always found wet on the under surface; and the grass below them was always much wetter than that freely exposed outside. The moisture rising from the ground was evidently trapped and condensed, instead of being allowed to pass freely into the atmosphere.
The explanation of the absence of dew on the surface of stones, roads, and other hard surfaces, on the old theory was, that these, being poor radiators, did not get much cooled. But closer observation shows that dew does form on stones and clods and gravel, only it is chiefly on the under surfaces. Thus, slates laid over both hard and gravelly roads are always found dripping wet on their under surfaces on dewy nights; while their upper surfaces and the surrounding roads are dry. During frost, too, clods and stones on the surface of the soil are almost always found to be covered with hoar-frost, showing that the moisture is trapped as it rises from the soil.