When The Dew Falls
( Originally Published 1907 )
"Everything shone with the dew drops that sparkling and trembling lay
ONE of the most interesting and instructive phenomena in the lessons of nature is the falling of the dew—a seeming miracle which begins with the setting of the sun, and goes on mysteriously, collecting and distributing its countless exquisite water jewels, all through the long stillness of the night, only to be dispelled again by the heat of the rising sun.
We are more or less familiar, through casual observation, with the varied beauties of the dew. A walk in the country or park, in the early midsummer morning, just after the sun has risen, if possible, will enable you fully to appreciate its charms; especially if the dewfall during the preceding night has been a copious one. Every bit of plant-life and vegetation will sparkle and twinkle in the early sunshine, hung and embellished with mil-lions of glittering jewels. The very smallest grass blade, you will discover, has not been neglected by the Dew Fairy. And even the delicate, gossamer-like spider's web swung from twig to twig or caught among the grasses, is dew laden, and an object of beauty well worthy of consideration.
Happy indeed are you, if you have enjoyed a stroll in an old-fashioned country flower garden in the early morning. No need to dwell upon its charms if you have enjoyed that pleasure, for you will long remember the refreshment and peace which came to you with the close companionship of the great pink, damask roses, their petals still heavy with the night dews; the tall, sentinel-like lilies, cool and fragrant, their cups filled with dewy nectar, which great blundering bees were eagerly plundering; clean-smelling phlox, waist-high, each velvet cluster moist and bent with its weight of dew. Then the beds of gray-green mignonette; and best of all, down in an out-of-the-way corner, a tangle of unobtrusive old-fashioned pinks, where you knelt and buried your face for a moment to inhale their spicy fragrance, and found them doubly sweet and satisfying after their drenching dew bath. While the beds of simples and humbler things, the sage and wormwood, with their silvery leaves heavy with dew, exhaled a pungent, aromatic odour as you brushed them in passing. For the dew had refreshed them and enhanced their dormant spiciness tenfold.
The phenomenon of the dew is simply explained, and well worthy of a short study, as it is really a most important factor in nature's laws. Simply explained, the dew is really an actual deposit of water from the atmosphere upon the surface of the earth, and is formed when the earth is sufficiently cooled during the night by radiation.
Upon a pleasant day during summer, especially if the sun shines brightly, much aqueous vapour or mist is held suspended in the air, and if the temperature at sun-set falls below the dew point, that vapour can no longer be retained in suspension in the air, and falls to the earth. The dew is the vapour of the air. Sometimes it can readily be seen falling in a fine mist resembling rain. It is the humidity of the air deposited upon all surfaces of the earth with which it comes in contact. When the temperature falls below the dew point, or 32°, the dew then becomes converted into frost, and we have a deposit of hoar frost, instead of the dew. It has been remarked that horizontal and flat surfaces exposed to the dew receive a greater deposit than sheltered or oblique surfaces.
Dew has frequently been quoted as "A shower from heaven," but this is not literally correct. True, it appears rather mysteriously from a clear sky, and upon a still, cloudless night covers thickly every blade of grass and plant life with seeming raindrops, and that frequently where rain clouds rarely appear, and the rain seldom falls. In such climates, where a rainfall is rare, it is certainly a most beneficial and wise provision, for it gathers upon all herbage and vegetation, in sparkling, refreshing profusion; while it avoids instinctively all barren rocky formations and all things which could not be benefited by its grateful cooling, moisture. Also, in cold, damp climates, where the air is continually saturated with moisture, and where an additional amount is not required, the gathering clouds and the dampness of the chilly atmosphere prevent a radiation of heat from the earth, and the dew never falls in such climates.
There are three requisites which appear to be essential for the formation of the dew: First, that the air should be moist; second, that the surface upon which it falls shall be cold, and third, that the sky be clear.
Of course the atmosphere always contains a greater amount of moisture after a rainfall, when the air has been greatly cooled. Evaporation is then continually going on among all objects lying near the surface of the earth. Blades of grass and all plants near the ground gradually cool and assume a lower temperature after sunset; they are preparing for the fall of the dew.
It has been remarked that certain plants possess greater powers of radiating heat and of expelling moisture through evaporative process than others; upon such plants the dew deposit is always more profuse, while those plants possessing less powers of radiation and evaporation, collect little dew.
There are very many plants whose leaves are downy, with a thick growth of tiny vegetable hairs; the mullein leaf is a good example, its thick velvety leaves are thickly covered with this growth of vegetable down, and present a velvety surface; these leaves always collect a fine display of dew jewels. One has been caught by the camera, perched upon the down of a mullein leaf, as shown in the photo-graphic illustration.
During still nights in early spring and fall, when there are no disturbing winds, the water molecules or dewdrops in countless numbers form one upon another, all night long, and settle upon blades of grass and all growing plants, and in the morning sunshine dance and sparkle in strings of scintillating diamonds from every pasture and hedge row.
The sharp-pointed grasses collect the dew very copiously and in a most interesting manner. Dewdrops formed upon the grass blades, it will be observed, are arranged in a truly wonderful symmetrical fashion, and one marvels at the orderly arrangement. Frequently one large dew-drop, clear as a diamond, is deposited upon the very tip of the little grass blade, sometimes two and even three large drops are held in suspension thus, while upon the extreme sharp edge of one or both sides of the blade a collection of small, bead-like drops cling in orderly, precise fashion, strung from tip to root of the grass blade. A broken or blunted blade of grass collects no dew, or very little. When the large dewdrop perched upon the tip of the grass blade decides to fall, it descends rather slowly at first, following the extreme edge of the blade in its course, and thus meets and collects all the other dewdrops which it encounters strung along the edge of the blade, until forming at last one heavy drop, it suddenly falls to earth, where it is instantly absorbed, and goes to give life and strength to the very roots of the plant.
Cobwebs attract the dew in a rather singular manner. It is yet to be discovered why the dew forms only upon the horizontal threads of a spider's web, while the vertical threads, though smaller, collect no dew deposit. This curious fact is well shown in the photograph of the entire spider's web, also in the section of a web, showing the dew deposit in detail. Wonderfully beautiful are these dew-laden webs. It will be observed that each drop is similar in size, and closely resembles several strings of well-matched pearls, although in the sunshine they appear as clear, flashing diamonds. Certain leaves collect the dew drops in a novel manner, notably the strawberry leaf, and similar plants having serrate edges. The strawberry leaf, besides being plentifully decorated upon its surface with water beads, holds in each tiny serration about its edge a large, clear, sparkling dewdrop, which gives the leaf a wonderful jewelled effect.
We are all familiar with the so-called "sweating" of a glass or pitcher, or a metal pipe containing cold water; this is another phase of the dew, and may be observed in the daytime.
A cool night in spring or autumn, after a hot day, we usually receive a more copious fall of dew, which gradually in-creases as the night becomes cooler. Should clouds gather, the precipitation of the dew at once ceases. Wherever a bush or bit of vegetation overhangs a spot, it has a similar effect to that of a cloud, and the dew does not collect at all, or not as copiously, in that spot.
In the tropics, and in certain countries where there are no rain clouds; where they rarely have rain for many months at a time, the dewfall is so heavy that it quite supplies the lack of rainfall. If it were not for this providential visitation of the dew all vegetable life must certainly perish, scorched and withered by the torrid heat.
In the East, in the region of Palestine, the dew frequently is so heavy that it closely resembles rain. Upon the great burning deserts alone the dew never falls; for the moment the dew vapours or molecules encounter the scorching breath which arises from the face of these barren seas of sand, they evaporate and are redissolved, dissipated and consumed by the heat. So it will be seen that the fixed molecules which compose vegetation alone have the power to attract and arrest the water molecules of the air with which they come in contact, and thus form, in combination, the dew.
When the temperature is below 320, the tiny particles which go to form the dew become hoar frost. It is often of great value to the farmer or vegetable grower to be able to know just the temperature of the dew point, because, if he discovers it in time, he is enabled to save his garden from a sudden blighting visitation of the frost.
Another interesting fact, and one which is known to few of us, but which may readily be seen, if we take time to study the dewdrop minutely is; that each tiny drop of dew is in itself a miniature mirror, for upon its clear, crystal-like surface it holds and faithfully portrays upon its rounded form the image of any near-by object. The picture is, of course, naturally inverted. But you will find it; a bit of blue sky holding a scrap of fleecy cloud, or a pigmy forest of trees caught and mirrored in the dewdrop. Often sleeping and dormant insects when caught out in the open during the night, receive a copious deposit of dew. The caterpillar shown in the photograph was a good subject, and quite a collection of dew was deposited upon his furry coat.
Nature in all her moods, and they are many, is always entertaining and instructive, and perhaps one of her greatest marvels is that which takes place in the silence of the brooding night—the falling of the gentle dew.