Fog signal

“ If, however, the signal arm should be lowered to the "all-right " position before a train reaches it, the fogman should immediately remove the detonators and exhibit a green flag or lamp, replacing the detonators as soon as the signal is again raised to danger. As a rule the fogmen are drawn from the ranks of the permanent-way men, who otherwise would be idle. But if, as sometimes happens, a fog continues for several days, great difficulty is experienced in obtaining sufficient men to carry on this important duty without undue prolongation of their hours of work. ”

“ Even the most important of all, the distance at which it ceases to be heard, is undecided.
"'Up to the present time all signal-sounds have been made in air, though this medium has grave disadvantages: its own currents interfere with the sound-waves, so that a gun or bell which is heard several miles down the wind is inaudible more than a few furlongs up it. A still greater evil is that it is least effective when most needed; for fog is a powerful damper of sound.'"
Dr. ”

“ OUR most intense coast-lights, including the six-wick lamp, the Wigham gaslight, and the electric light, being intended to aid the mariner in heavy weather, may be regarded, in a certain sense, as fog-signals. But fog, when thick, is intractable to light; the sun cannot penetrate it, much less any terrestrial source of illumination. Hence the necessity of employing sound-signals in dense fogs. ”

“ In foggy weather audibility is often better than the average, because fog prevails chiefly when the air is still and of uniform temperature, and such conditions favor the transmission of sound. Tyndall strongly denied that either fog or falling rain, snow, and hail have, as has been commonly believed, a muffling effect on sound, and he attributed the peculiar behavior of fog signals to the presence in the atmosphere of invisible “acoustic clouds,” consisting of patches of air containing irregularities of temperature and humidity. ”

“ Experiments and observation lead to the conclusion that these anomalies in the penetration and direction of sound from fog-signals are to be attributed mainly to the want of uniformity in the surrounding atmosphere, and that snow, rain, and fog, and the direction of the wind, have much less influence than has been generally supposed. ”

“ In a lecture at the Royal Institution, Dr Tyndall has made known the results of a long series of experiments on fog-signals, all involving more or less of noise, and demonstrating that the noisiest are the best. Mariners in a fog are helpless: no lights, no cliffs, no towers can be seen, and they must be warned off the land through their ears. ”

“ He knew that they would never give him up till they assuredly knew his fate, but would follow after him, and set other vessels on the search, till the whole bay, with all its shores and islands, should be thoroughly ransacked.
Fortunate was it for him, he thought, that there was so large a supply of drift-wood at hand on the beach, dry, portable, and in every way convenient for use. Thanks to this, he might now disperse the gloom of dark and foggy nights, and keep up a better signal in the dark than he could do in the light. ”

“ The details of cloud photography are described in the Monthly Weather Review, August, 1920.
the chilling of the air progresses. Advection fogs are more apt to follow gentle movements of the air; gale winds may create mixing to the extent that dew-point temperature is not reached. The advance of a cold wave moving gently into a region of warm, moist air—the fog in front of a high—is an example of advection fog. ”

“ A vast bedlam of sound flies up to my window, and above all is the immense whistling of unseen and unfelt winds.
"The fog has again swept over the city and the whistling is coming closer and closer.
"It is now directly beneath me.
"God! An instant ago the mist opened and I caught a glimpse of the streets below.
"The fog is not simply vapor -- it lives! By the side of each moaning and weeping human is a companion figure, an aura of strange and vari-colored hues. How the shapes cling! Each to a living thing!
"The men and women are down. Flat on their faces. The fog figures caress them lovingly. ”

“ They will prove a much greater hazard to air transportation unless a circuitous southerly route is followed. An Arctic current and a southwest wind laden with water vapor constitute the working machinery of this fog factory. Radio-telegraphy now forewarns the sailing master when and where he will encounter the fog blanket that hovers over an ocean graveyard. ”

“ If this is primarily the result of movement of air over a surface of lower temperature, it is called advection fog; if primarily the result of cooling of the surface of the earth and the adjacent layer of atmosphere by radiational cooling, it is called radiation fog. An advection fog occurring as monsoon circulation transports warm moist air over a colder surface is called a monsoon fog. A fog that hides less than six-tenths of the sky, and does not extend to the base of any clouds is called a ground fog. ”

“ There one at least could see the light of the binnacle, but last night I could not even distinguish the hand by which I guided myself along the barrack wall. At sea a fog is a natural phenomenon. It is as familiar as the rainbow which follows a storm, it is as proper that a fog should spread upon the waters as that steam shall rise from a kettle. But a fog which springs from the paved streets, that rolls between solid house-fronts, that forces cabs to move at half speed, that drowns policemen and extinguishes the electric lights of the music hall, that to me is incomprehensible. ”

“ The factors themselves are moisture, dust, smoke and refraction of light. The dust and smoke differ merely in origin; the moisture may appear in the form of fog, mist, rain, or snow.
Fog, Cloud, Mist.—In marine transportation, fog is the worst factor in the impairment of visibility. Practically it is the only one. If the temperature is brought below the dew-point, fog results from condensation of the water vapor. The brisker the wind, the thicker the fog blanket. A convectional updraught does not destroy the turbulence; convection merely carries it higher. ”

“ Powers and limitations of the acetylene signal lantern.—As conditions are usually more uniform at night than in the daytime, the signal lantern is probably the most reliable of all visual signaling outfits. The advantages of this form of apparatus are its portability, speed of operation, and comparatively great range. The principal disadvantages are due to the interference caused by rain, fog, and moonlight. The speed attainable with the lantern is about the same as that attainable with the heliograph. ”

“ Fogs happen at night, when the air has been saturated with vapour during the day. When this is the case, it deposits some of its superabundant moisture in the form known in rural districts—as my Hon. Friend, the Member for the Bordesley Division, is well aware—as dew. In the Metropolis it is more familiar as fog. This process of deposition commences as soon as the capacity of the air for holding vapour is lessened by the coldness of advancing night. I think I have now answered the question of my Noble Friend fully, and, I trust, frankly. ”

“ Last but not least, the artificial dispersion of fog by means of electrical discharges, although still in the experimental stage, holds out possibilities of being the ultimate solution of the fog problem, not only for the aeronaut, but also for the mariner, the railway manager, and everybody else who is incommoded by a misty atmosphere.
303 Even when he is not flying in clouds or fog the aviator by no means always enjoys a clear view of distant objects. A slight haze impairs visibility, while a heavy rainstorm or snowstorm may obstruct the aeronaut’s view as badly as a fog. ”

“ Mayo?” shouted Captain Wass.
Fogs are freaky; ocean mists are often eerie in movements. There are strata, there are eddying air-currents which rend the curtain or shred the massing vapors. The men in the pilot-house of the Nequasset suddenly found their range of vision widened. The fog did not clear; it became more tenuous and showed an area of the sea. It was like a thin veil which disclosed dimly what it distorted and magnified.
In a fog, experienced steamboat men always examine with earnest gaze the line where fog and ocean merge. ”

“ Likewise when the wind has been blowing over a warm ocean current, the surface of the warm water evaporates and fills the air with water vapor. Then when this air passes over a cold current, the cold current cools the air so much that the moisture in it condenses and forms fog. That is why there are fog banks, dangerous to navigation, in parts of the ocean, particularly off Labrador.
Why you can see your breath on cold days. You really make a little fog when you breathe on a cold morning. ”

“ To a certain extent they are of the nature of city fogs, being encouraged by the smoke and dust incident to city industries. In the larger harbors fog may be forecast, but not with a high degree of verification. Even a light fog ties up shipping pretty effectually. ”

“ Again, in the example of our London fogs, &c., when in the upper portion of the dense mass the blue rays have been all refracted, there can penetrate only those other rays which make the lurid sky, with which we are familiar, or the genuine old yellow fog. Fog in moderation, the thin vapor on the open sea, and so forth, simply gives a lightness to the blue tint, or more plentiful, an absolute whiteness to the atmosphere. ”

“ In an hour its lofty crest had ascended far up into the sky.
"It's a comin," said Captain Corbet. "I knowed it. Grind away, you old fog mill! Pile on the steam, you Grand Mananers!"
"Is there any wind down there?"
"Not a hooter."
"Is the fog coming up without any wind?"
"Course it is. What does the fog want of wind?"
"I thought it was the wind that brought it along."
"Bless your heart, the fog takes care of itself. The wind isn't a bit necessary. It kine o' pervades the hull atmosphere, an rolls itself on an on till all creation is overspread. ”

“ In the vessel containing common air the steam will be seen rising in a dense cloud; then a beautiful white foggy cloud will be formed, so dense that it cannot be seen through. But in the vessel containing the filtered air, the steam is not seen at all; there is not the slightest appearance of cloudiness. In the one case, where there was the ordinary atmospheric dust, fog at once appeared; in the other case, where there was no dust in suspension, the air remained clear and destitute of fog. Invisible dust, then, is necessary in the air for the formation of fogs. ”

“ In sultry days, and, indeed, in all weathers, navigators are much harassed in those seas by the fogs; they, however, chiefly occur towards the latter end of summer. They are excessively dense, and at a distance are frequently mistaken for land. In winter, when the cold is intense, a vapour called fog smoke frequently arises from the chinks of the ice, which is so acrid as to excoriate the face and hands of those who approach it. ”

“ The persistent fogs of the Newfoundland Banks are due to the passage of warm moist air from the Gulf Stream region over the94 cold Labrador Current. On the other hand, a cold wind blowing over warm water will also often produce a fog by lowering the temperature of the moist air overlying the water. A common cause of land fog is the cooling of the air adjacent to the ground in consequence of nocturnal radiation. The moister the air, the more readily fog forms, and hence the frequent formation of fog by night along rivers and over marshes and damp valleys. ”

“ It is, as already shown, an opinion entertained in high quarters that the waves of sound are reflected at the limiting surfaces of the minute particles which constitute haze and fog, the alleged waste of sound in fog being thus explained. If, however, this be an efficient practical cause of the stoppage of sound, and if clear, calm air be, as alleged, the best vehicle, it would be impossible to understand how to-day, in a thick haze, the sound reached a distance of 123⁄4 miles, while on May 20th, in a calm and hazeless atmosphere, the maximum range was only from 5 to 6 miles. ”

“ In the country it is disagreeable enough; but never so intensely raw and dense as in the city. On the sea, too, the fog is disagreeable and fraught with danger. The fog-horn is heard, in its deep, sombre note, from the lighthouse tower, when the strong artificial light is almost useless. ”

“ City fogs, which are due largely to pollution, cannot be forecast. They are indicated when the humidity is high and the smoke pollution great. They disappear with a slight rise of temperature. It is well to bear in mind that, with temperature close to the dew-point, a fall of a very few degrees may fill the air with a dense fog; a rise in temperature ever so slight may change foggy air to clear air. Impairment of visibility due to smoke pollution cannot be forecast. When due to a lid, a rise of barometric pressure indicates a clearing of the air, which may take place in an hour. ”

“ The outlines of an object which normally is distinct may be obliterated, but its mass is likely to be seen. In this respect rain differs from fog. Even if the combined surface of the drops next the observer is sufficient to form a screen, the screen is partly transparent, but a fog screen is practically opaque. If a rain-drop be broken into water particles of fog size, their aggregate surface is several million times that of the rain-drop. The screening power of the fog, therefore, is vastly greater than that of the rain-drop and so also is the amount of light scattered. ”