Chapter IV: Sky Signs for Campers (2)

Contrary to superstition snow may begin to fall at any hour of the day or night. But certain hours seem more propitious than others, owing no doubt to the tendency of cooling air to condense. Three o'clock of an afternoon and eight o'clock in the morning are favorite times, the one being the hour of a winter afternoon when cooling is begun, the other the hour when the coldest time is reached and condensation likely if at all. Of course, one remembers storms beginning at nine, ten, eleven, and every other hour.

Storms that begin in the morning seldom reach much activity before three o'clock in the afternoon, while those that begin then quickly increase in intensity as evening draws near and the sun's warmth is withdrawn from the upper air-strata. More snow falls at night than in the daytime, also. Snow is more delicate than rain and perhaps more responsive than rain to the subtle changes of the atmosphere. Possibly there is no ground on the Bureau records for these ideas, possibly storms have a tendency to start from the Gulf on their northeastward journey and so reach Philadelphia oftener at one time than another. I would like my notions confirmed that snowstorms increase at nightfall, and that they prefer to start operations at sunrise and about sunset.

For the camper the snowstorm need have no terrors. It gives a long warning of its approach. It comes mostly without destructive winds. Its upholstery protects and warms the walls of one's tent. It adds beauty to the leafless woods, interest to the trailer, and a hundred amusements among the hills.

But the value of snowy weather is not only measured by its beauties and commercial uses. There is another way: make it read character for you. Watch the reactions toward the first snowfall of half a dozen kinds of people. It will show you what they are; give you a very fair measure of their youth.

Our atmosphere contains a lot of moisture that never gets precipitated. You can prove this on any warm day by noticing the way the atmosphere acts toward a glass of ice-water. When the air of the room is much warmer than the surface of the glass it surrenders its moisture willy nilly. Sometimes this condensation is enough to cause a miniature rainstorm that trickles down the outside of the tumbler. If a small cold surface can wring so much water out of a little air it is small wonder that we get an inch or so of rain from vast currents of air at unequal temperatures.

Try to visualize the process. A stream of vapor has been warmed and is ascending. A mile up and it has cooled not only by the reason of altitude but also by the process itself. About each little dust-particle in the surrounding area vapor forms--vapor cannot form without something to form on, there being always enough dust from deserts and volcanoes to go round. If the cooling proceeds the tiny globules enlarge and as they increase in weight they settle and fall. Falling, they unite with others.

If the air-strata are very warm and thick the drops may grow to a very considerable size. We see these in the middle of our great winter rains when the insweep of southern winds with all their warmth and moisture is very extensive. Also the first few drops that come from the thick, hot lips of the thundercloud are usually immense.

The best way to measure the size of a raindrop is to have it fall in a box of dry sand. It rolls up the sand and measurements can be easily and accurately made. But the most interesting way is to let the first drops of the thunderstorm fall upon a sheet of blotting paper. If the same sort of blotting paper is used the measurements will be of just as much importance for comparison. Circles as big as teacups are formed sometimes.

Heavy drops in winter mean a heavy fall, because they denote high temperatures which are uncommon and are bound to be followed by considerable condensation as the cooling proceeds back to normal temperatures. Small drops in summer mean either cooler weather, or sudden condensation. Small drops in winter are a sign of very thin moisture-bearing strata, or low temperatures, indicating that the rain will be light, protracted, and liable to change to snow.

Hail is frozen rain. Winter hail is small and harmless and rarely falls to any depth because the exact temperatures that bring forth the hail rarely continue for very long at a time. Hail in winter is merely the stepping stone to either rain or snow. But in summer hail is a serious matter. It shows that there is a violent disturbance of the atmosphere in progress. Vertical air currents, probably abetted by electricity,--the authorities are not sure--often carry the stones up several times. They take on layer after layer, coalesce, and sometimes fall the size of eggs, apples, or any other fruit, barring melons. The usual summer hail does not exceed the size of a robin's egg. Even a projectile of that size, however, falling for a half mile or more has a tremendous destructive power. Greenhouses suffer, birds are killed, cattle stunned, and loss of life has been known to follow. In August in 1851 in New Hampshire hailstones fell to the weight of 18 ounces, diameter 4 inches, circumference 12 inches. In Pittsburgh stones weighing a full pound have crashed down, and in Europe where many destructive storms have occurred there are official records of even greater phenomena. The lightning accompanying these hailstones is usually very severe. A flake or ball of snow forms the nucleus of a hailstone.

If a thundercloud looks particularly black or if it can be seen in commotion think of hail and seek shelter. It is pretty difficult to predict exactly when hail is going to fall in summer. It is a possibility with every large storm, but a probability with only a very few during the summer. It accompanies tornadoes.

In winter hail falls before a rainstorm, even when the ground temperature precludes the possibility of snow; some lingering stratum of cold air has ensnared the drops on their way down.

Snow is not frozen rain. It has an origin of its own. It is born in a temperature consistently below freezing and on the condensation of the invisible moisture becomes visible as a tiny crystal. These infinitesimal crystals unite and form larger, hexagonal shapes, elongated or starry. They are wafted along, sinking, all slightly differing one from another, although forming a few types. These types have been photographed and catalogued and very often the altitude from which the snow is coming may be learned from their shape and design. But this branch of science is young yet and confusing and the outdoor man has surer signs of the vicissitudes of the storm, in the general size of the flakes, the power and direction of the wind, the clouds and temperature. The possibilities of flake-study as a means of forecasting are many and of value as is anything that tends to unveil the secrets of the greater heights.

Snowflakes are so light that after the storm processes are over and the sun has come out the residue may still float lazily to the ground.

The wild disorder of the snow flurry will only last a few minutes and never leave much snow on the ground.

Snowstorms that come on the wings of the west wind may be severe, but they will be short. They are unusual in the east, but sometimes the heaviest snows of the western states come on the sudden cooling that follows the shift to west.

Snowstorms arriving on a high wind last only a few hours.

Snowstorms that are long in gathering and increase to considerable intensity continue a long while.

Those that follow a sudden clouding up are of no importance.

The snowstorms that leave on a high wind from the west or northwest are followed by a cold wave. Those that continue after the storm wind has died away are succeeded by calm, clear, and usually warmer weather.

In northern districts a snowstorm may be looked for after a period of cold weather. In middle districts if the cold has been severe the reaction to warmer may bring rain instead. In such cases generalities are of no use, and the possibilities must be determined by the man on the spot. The best conditions for snow through the middle districts are occasioned by an area of low-pressure with its attendant precipitation crossing the southern half of the country while the northern half is under the influence of an area of high-pressure with its attendant frigidity. The cold air flows into the southern storm with the result that the middle districts get the northern quadrants of the storm which are the usual snow-bearing ones instead of the southern rain-bearing quadrants that they would have got if the center of the storm had pursued its usual course up the Ohio and down the St. Lawrence.

If the storm has two centers, one over Texas and the other over Montana, as is so frequently the case in winter, the subsequent high pressure will come too late to affect the temperature of the zone of precipitation and the latter will likely be rain in the middle districts. Sometimes the cyclones cross the country on the Canadian border and enough warm air is sucked over the line to give the inhabitants of Montreal a thaw and rain. This happens to them only once or twice a winter. And even more rarely a cyclone over the Gulf with an anticyclone above it will give the Gulf States a taste of winter, but rarely more than a few flakes.

It really all depends on the influx of air, its rate and direction. It rains in Alaska and snows in Georgia on the same day merely because at one place the air is coming off the Pacific, and at the other it is flowing from the center of a refrigerated continent.

And the progress of these storms is one of Nature's greatest poems if you take a minute to think of them sweeping on in majesty, the one thing that man cannot control. Even the snow which is the citizens' curse as well as the farmers' blessing becomes epic when it beleaguers an empire for half a year.

DEW AND FROST

The very process that made the tumbler of ice-water sweat on the hot day causes dew. And the formation of frost is analogous to that of snow. Frost is not frozen dew, but the formation of moisture crystals at the temperature of 32 deg. or below. Frost or dew form only on still, cloudless nights. Even if no clouds are visible, neither will form if a stratum of humid air has prevented radiation. Hence either dew or frost is a fairly good sign of clear weather.

Three white frosts on successive mornings are followed by a rain. This saying holds water not because there is any virtue in frost to cause rain, but because a storm is normally due once a week. The frosts did not form when the anticyclonic winds were blowing and usually not more than three mornings elapse between the time that the anticyclone has lost its influence and the time for the next cyclone to appear. Frost indicates a considerable amount of moisture in the atmosphere, also, which tends to increase as the cyclone approaches.

The heaviest dews come in late summer and the heaviest frosts in mid-autumn because the change in temperature is greatest then and there is a greater chance that there will be a calm at sunrise. The greatest frost damage occurs in the spring because the tenderer crops are growing then. Summer frosts used to occur in the northern parts of Minnesota and along the southern boundaries of the inland Canadian provinces before the forests were cleared off. The march of civilization has actually pushed back the frost line some distance.

Frost may occur when the amount of humidity in the air is low and the barometer rising at any temperature under 50 degrees at nightfall, the clear skies permitting radiation enough under those circumstances to produce the necessary cooling. An evening temperature of 40 degrees with the clear skies and faint west breeze will almost surely produce a frost, provided the wind drops. In such circumstances the only hope for the farmer is that there is enough humidity in the air to cause a fog before the frost-point is reached. A temperature touching 34 degrees would not bring frost, however, if the sky was at all overcast. Frost is difficult to predict because a night shift in the wind, cloudiness that forms after midnight, or even a wind arising before the coolest period at dawn will prevent its formation. On the other hand, clouds may disperse, the wind may fall or radiation may be so rapid before sunrise as to cause a killing frost unawares. The farmer who lives in areas disputed by winter and spring may never be quite sure, but precautions should be taken on the still, clear, dry nights with the thermometer at fifty or below.

Fruit-growers resort to fires or to coverings to protect their crops. The fires are particularly worth while, not so much for their heat which at best cannot be expected to warm up the great outdoors much, but for the smoke which prevents radiation. A line of smudges such as campers use to ward off the mosquito would spread a pall of smoke over an orchard efficaciously. A snowstorm, the soft fluffy sort that falls in April or May, can do much less damage to vegetation than a severe frost.

Temperatures are much lower on the ground than even six feet above the grass. Naturally these temperatures are those that really influence most vegetation and in England temperatures on the grass are given in the weather report with the ordinary observations, being as much as six or eight degrees lower on clear nights.

In some of the hot, dry countries, such as Arabia and Egypt, most of the moisture that they receive falls in the form of dew. Falls, of course, is a loose expression as the dew forms and does not fall, being different from the minute particles of fog. The fog particles in suspension in the air are estimated to be as small as 1-180th of an inch. When they grow to 1-80th of an inch in diameter they commence to fall. Fogs are chiefly caused by the soil being warmer than the air above it; the vapor on rising condenses and becomes visible. In the spring and fall currents of air blow over rivers at different temperatures and the result is a fog. One does not have a fog in the desert.

There are places in the ocean with cold and warm currents with the air above them correspondingly different where fog is of almost constant occurrence. The Gulf Stream off the Grand Banks of Newfoundland has a temperature of 78 degrees, while the water on the Banks is 45 degrees so that fogless days are rare along the line of meeting.

Frost is known in every part of our country, many localities in the plateau section being exposed to it every month of the year. The thin air and cloudless skies of the altitudes make radiation very easy and the daily variation of temperature is much wider than along the humid coasts. Those who have never looked into frost conditions throughout our country will be surprised to read the warnings of the Weather Bureau.

From the station at Pensacola, Florida (frost-proof Florida!), comes this statement: "Vegetables are subject to damage by frost during all seasons of the year."

Pittsburgh, Pennsylvania, "Frost is likely to damage fruit or other crops in May and September."

Phoenix, Arizona, "Frost is likely to do damage in December, February, and March."

Baker City, Oregon, "Fruit and other crops are most liable to damage by frost in April, May, June, September, and October."

Kalispell, Montana, "Frost damage for fruit, May 15th to July 10th; for grain, June 25th to August 1st."

Montgomery, Alabama, "During March, April, and May fruit and early vegetables are subject to damage by frost."

THE THUNDERSTORM EXPOSED

Probably nothing in the world causes more terror than a flash of lightning. In an able-bodied thunderstorm playing about a city there are several dozen flashes, and every one of them brings trepidation, fright, or positive terror to thousands of human beings,--oftenest women, sometimes men, and occasionally children. Yet probably there is no alarm in the world so ill-founded.

Thunderstorms play pretty generally over our three million square miles with their hundred million population. Yet lightning picks out of this crowd only three hundred people a year who are foolish enough to be killed. That is, only three persons in each million to be sacrificed to the most astounding and beautiful display in the world, a mere handful compared to the mounds of motor car victims or to the 33,068 deaths a year attributable to railroads and the perils of track-walking.

The trouble about the thunderstorm is that it does not lull one into the sense of insecure repose. It is too obviously after one. If the thunder were toned down a bit and the lightning a trifle duller the alliance might claim its thousands, like the inconspicuous housefly, and never meet an objection. But until the thunderstorm foregoes its bravado it will continue to bully the ladies into hysterics.

Of course, there is always the sporting chance that you are one of the three in your particular million to perish.

But you can lessen the chance. You must not seek refuge under a tree. You should not take doubtful shelter in a barn. And you had best not sit in a draft by an open window if there is a tree just outside it. By these three avenues most of the thoughtless three hundred (a year) invite their end.

Trees that are tall and otherwise exposed are struck oftenest. The electricity in the cloud and the electricity in the earth are always endeavoring to combine. When this tendency becomes so strong that the resistance of the intervening air is counteracted the electric discharge between thundercloud and earth takes place. This happens most frequently from some pointed thing as a steeple, a tree if they are good conductors. Men and animals are sometimes charged with the electricity opposite to that of the cloud. When the lightning is discharged, even at a distance, the bodies revert rapidly from the electric to the natural state. This return shock or concussion occasionally proves fatal.

That is the reason that trees are such poor protectors from the storm's fury. Better a wet skin in the middle of a field than precarious dryness under an oak or cherry or tall pine or almost any other tree. If it should hail hard enough to stove in your head take to a beech or a small spruce.

Barns are struck so often because the body of warm, dry air in them favors the passage of electricity. Those who hide in barns are sometimes cremated. After a severe thunderstorm in the Poconos I have seen as many as three barns on fire at once.

Open windows, porches, and exposure generally are safe, but not safest. The cellar, that old stamping ground, is where instinct takes a few. Any closed room on the side of a house away from trees is good enough. But the risk of annihilation is so very small that one is repaid for taking it by the spectacle. A great thunderstorm surpasses anything in nature in the matter of architecture, coloring, directness, and surprise,--which, with selection, comprise the essentials of art. Imagine the crowds that would pay to wonder at the sight if a thunderstorm could be staged, say, at the Hippodrome!

Some hot morning, if you have time to watch, you may see a thunderstorm born in the mountains. The warm, moist air flows up the mountainside and the essential start is made. Cooling, this air first shows as a fluffy cloud that soon grows harder in appearance and becomes tufted at the top. Its little belly swells and grows blacker. It hovers over the valley. Others add to it. Suddenly a sort of adolescent thunder is heard. The tension has become too great. A definite consolidation is visible, a fringe lowers, and a few drops of rain may reach you.

The incipient storm moves off, and having started a whirl within itself, increases, like a rumor, as it goes. Before it has moved beyond your horizon it may have become a large patch of dark blue with billowy white crests on the top, and underneath hangs a curtain of rain. Chances are that it will not go far before encountering conditions that dispel it, but it may cover half a dozen counties before nightfall. As a rule these little heat thunderstorms do not amount to a great deal. They are originated by local conditions and leave things pretty much as they found them.

But when a cyclone is passing in summer a series of thunderstorms or heavy showers with some thunder frequently take place instead of the all day winter rain. These thunderstorms mount up against the wind. Their clouds are black. The word black is an indulgence of the human weatherman meaning, of course, any dark color,--a black sky would terrify the most hardened of meteorologists.

The cyclone winds come from the south or southeast just as they do in winter, but this quarter may not bring the heaviest rainfall in summer. There may be showers or even clear skies, but the day will be humid and hot. A haze of cirro-stratus cloud will gradually overspread the sky from the west, darkening into a blue from the original whitish or gray. Lightning does not appear from the cirrus, but after the sky has grown pretty dark a ridge or tumbled cloud will be seen low on the western horizon. Meanwhile the wind will have died down.

The lightning, at first only a faint glimmer, will have become more frequent and noticeable. If it is striking at a distance of fifteen miles the thunder will not be heard. As soon as the storm center, where the heaviest rain and the electrical display are taking place, gets within the fifteen-mile radius thunder will be heard to growl, and the tumbled cumulus clouds which may have lain along the horizon for hours will begin to approach. The storm will be upon you in ten minutes likely after the arc of foreboding blue and white cottony cloud has begun its charge across the sky. Light quickly fades from the heavens. The wind drops entirely. Streaks of lightning burn downward.

Behind the arc stretches a curtain of uniform blue or gray. If the gray is lighter in places the rainfall will not be heavy. If the curtain is a uniform blue a heavy rain is sure. If the bow of clouds can be seen to tumble or is continuous and approaches fast the wind is certain to be severe,--may be from 30 to 60 miles an hour for the first few minutes. Sometimes a cloud of dust advancing before it demonstrates its force.

This moment immediately before the storm breaks is the dramatic moment of the entire cyclone. As in a tragedy, the interest has built up to this supreme occasion, this knife thrust, from which interest recedes until clear skies show that the play is over. From 12 to 36 hours is the usual time required in winter. In summer the cyclone takes even longer to pass a given point, but the period of rainfall, in which the winter storm's amount is often surpassed, may not last fifteen minutes. First the blow, then a crash of thunder, and the rain in big drops, which lessen rapidly in size as the whole world seems involved in the vast forces of the storm center. Most of the precipitation occurs in the first fifteen minutes, sometimes in the first five. A hearty storm will deliver an inch in short order. Although the rain continues often for an hour and sometimes in the storms that are attached to a well-defined cyclonic system there will be two or three robust thunderstorms in succession, yet the first downpour is usually the torrential one and the others die away until the conditions that caused the outbreak have passed off. With the severer storms hail falls.

The general condition of the air after a thunderstorm is cooler, dryer, and more invigorating than before. Ozone has been liberated, dust has been washed from the air and vegetation. The surest sign of a continuation of unsettled weather is the failure of the atmosphere to cool off. If the air remains sultry and heavy and depressing another shower is due. In such circumstances the wind will not have begun to blow with any great promise from the west.

A close, sultry morning is the best indication of a thunder-gust. The large piles of cumulus clouds are called thunderheads for the very reason that they almost always precede a thunderstorm. The heaviest electrical disturbances have cirrus clouds a few hours in advance of them very much as their winter relatives. A thunderstorm that does not cause the barometer to fall considerably will not amount to a great deal.

At night the different kinds of lightning furnish a running commentary to the storm. On calm evenings the sky will be cloudless, with perhaps the exception of a low rim on the northern horizon. Yet flashes of lightning, of course without thunder, may be seen illuminating that entire quadrant of the sky. This is called heat lightning and is popularly supposed to be the result of the heat only. As a matter of fact it is caused by a normal thunderstorm that is operating below the horizon. Reflections from this storm are shown on the rim of clouds, or if no clouds are visible, on the bowl of the sky. If you see lightning be sure that there is a storm somewhere.

If this disembodied sort of lightning continues to flash from the western sky it is quite possible that the storm will reach you. If it shows on the northwest or north of you the chances are that the storm will be carried around. If the wind is from the southwest and the lightning appears there only the progress of the clouds will show whether the storm is pursuing the normal track from the west and around you or whether it is edging up toward you. One cannot be very well surprised by a thunderstorm of any energy in camp as the lightning shows as much as two hours before the storm breaks and the thunder gives fifteen minutes' notice on most occasions.

The sort of lightning that spends itself illuminating the clouds in serpents and willowy branches confines itself to the altitudes and is very beautiful and harmless. It is accompanied by thunder that sounds hollow, that rumbles over the sky, and usually does not end with the crash and thud of the more vigorous variety. Such lightning and such thunder are more often connected with the sort of storm that comes up very swiftly on a western wind. It gives shorter warning than any other sort of thunderstorm and is not connected with the cyclonic area. I have known such a storm to manifest itself low in the west, approach, and break within twenty minutes. Much wind results and not much rain, although the temperature falls. Lightning with storms of this impromptu kind rarely does any damage.

But if the storm rises slowly against the wind, requiring an hour or two or three to approach and break, the lightning will grow almost continuously, some of the flashes being broad streamers cleaving the western sky. It is this sort of lightning that does the damage. The thunder, instead of rolling like an empty barrel, hits into a series of concussions. If the lightning strikes an object nearby the crash is rather appalling. There are several freak sorts of lightning such as the ball form, which are rare.

The approach of the center of disturbance may be gauged by the length of time that elapses between flash and crash. In reality the thunder occurs immediately after the discharge of electricity, but sound travels so slowly, compared to light, that a minute may intervene between stroke and clap. You may count the seconds, noticing the regular decrease, signifying the nearing of the crisis. Soon a flash in front and a simultaneous peal will show you that you are in the thick of things. The next bolt or two may hit very close and you can appreciate what it means to be on the firing line. Then the next river of fire with its detonation streams behind you and you are saved.

In a severe thunderstorm there are several centers, several nuclei that shed destruction like great batteries and their progress over and beyond you has its thrills. You may find the exact number of feet away that the bolt hit by multiplying the number of seconds elapsing between the lightning and thunder by 1120. But an easier way is to allow a mile for every five seconds on the watch. One or two seconds, and you are pretty near the center of the fray.

Lightning compresses the air, leaving a partial vacuum. The other air rushing in to fill this partial vacuum forms the wave motion that produces the noise. That is the whole why of thunder. The reason thunder rolls is that the lightning is a series of discharges each of which gives rise to a particular detonation. If lightning were but one discharge, the thunder would be but one stupefying crash. Reflections from the clouds and from layers of air of different densities and from the ground are agencies that prolong the sound.

Our atmosphere is never lacking in electricity. This electricity is always positive in clear weather and sometimes negative in cloudy. Science concludes, then, that negative electricity invariably indicates rain, hail, or snow within a radius of forty miles.

Moist air is a good conductor. Our powerful motors can now produce a spark of electricity several feet long. But some of the flashes that shoot across the sky in a big storm extend over five miles. The duration of the flash varies from 1-300th of a second to a second. The reason that lightning does not always pass imperially along a straight line is that some air, either moister or warmer than the air around it, offers less resistance. The lightning takes this line of least resistance along the pathway of warmer or less dense air.

Altitudes of thunderclouds vary. They may hover above the earth at 800 feet. They may be a mile high. They have been observed on peaks of mountains three miles high. Many other electrical phenomena are observed in the mountains. The study of these will undoubtedly benefit meteorology and perhaps go far to explain the unsolved problems of the Service.

One kind of thunderstorm that is rather rare is that which arrives in winter with the passage of an energetic cyclone. Often when the wind, having been in the southeast for most of the storm, is passing around and reaches the south or southwest the rainfall culminates in a deluge and thunder is heard. One or two such storms are a winter's complement. They usually terminate the rainfall for that particular cyclone. I have never heard of damage caused by these winter electrical storms, and they occur only in exceptionally well-developed areas of low pressure.

Lightning has many times been observed during heavy snow storms. I have never heard any thunder with it. The discharge must have been very faint.

_Courtesy of Richard F. Warren_

Stratus is merely lifted fog in a horizontal form, the lowest of all, and the simplest as regards structure. It means neither rain nor snow and the apparent clearness of the blue above it would indicate clear weather to come. But through the break in the stratus near the horizon shows a cloud of firmer texture, which is less reassuring. Stratus over the land in winter takes the appearance of long bolsters of gray through which a pale blue sky shines. Such clouds may blanket the sky for days without causing a drop of rain. If they show a tendency to glaze over expect snow or rain, but not in large quantities.]

The fascination that a thunderstorm has for many people is explained partially by the fact that one sees the whole process from beginning to end. The officials of the Weather Bureau have this privilege as regards cyclones. It is their business and pleasure to watch the setting up of these vast storms, to follow them on their journey. It is small wonder then that they find the spectacle fascinating.

THE TORNADO

The birds, the flowers, and the tornadoes are all busiest in spring. And the tornadoes probably make the largest impression.

A tornado is merely a whirl of air, caused, as are all the other whirls, by a striking difference in temperature in adjacent areas. A tornado is a local and restricted example of the same thing that a cyclone is. But a tornado rarely crosses more than a single state; a cyclone strides continents. A tornado lasts, in one place, about a minute; a cyclone affects the weather for three days. A tornado never survives the night; a cyclone plods on for a week. And yet if you are betting on destruction put your money on the tornado. What it lacks in the realms of space and time it makes up in intensity. Its sting is fatal.

Tornadoes occur chiefly in the spring because the temperature changes are greatest then and it is from these that the tornado sucks its nourishment. Over the plains, for example, a limited area is abnormally heated by a local cause. Abnormal cold comes in contact with the abnormal heat. The great difference in pressure results in a spiral as it did in the cyclone, only in a very small spiral, and once begun its energy is self-aggravating. The whole thing moves off toward the northeast attended by the black cloud of its condensation. From the black cloud a funnel like an elephant's trunk sways back and forth, now touching the ground and now escaping it. The black cloud has been in the southwest for some time probably before it has commenced to move. The day has been very oppressive. The sun rose rather coppery, in all likelihood. As the black cloud with the swaying funnel nears a roaring is heard. Darkness falls. The roar increases.... Instantly it is over.

Now that you've been through a tornado you know how it feels,--almost. After the funnel passes hail falls, lightning flashes through the lessening murk. Heavy rain succeeds, and if you're alive you go out and rescue the perishing.

The wind velocity in the path of a tornado is enormous,--anything up to 500 miles an hour,--but no instruments have been devised to withstand the strain. Varying pressures are responsible for the destruction. As the funnel passes over a house where the normal air pressure is about 2,000 pounds to the square foot it removes 1,500 pounds for an instant. Naturally the outside walls cannot withstand this enormous inside out pressure and the house explodes like a projectile. Only under such conditions could the vagaries of matter,--straws piercing logs and chickens bereft of every feather--be perhaps not explained but pardoned.

Stories of any degree of incredibility crop up after each tornado, often with accompanying photographs as proof. People are plastered with mud, pianos are deposited in neighboring lots, babies are hung up unhurt by their clothes in tree-tops, and often one person is killed and another nearby escapes unhurt, Bible-fashion.

Tornadoes may form almost anywhere, but they are never found on the immediate Pacific coast. They are most common in the Mississippi Valley, are rather common in the Gulf States, and have occurred throughout most of the East at one time or another.

Since there is no way of stopping them the next best thing is to know the conditions that make for their formation. If the Weather Bureau predicts a cold wave for sections of the country where the weather is already abnormally warm the line of meeting will probably produce a tornado somewhere. The officials, however, advise you not to worry until you see the intensely black cloud in the southwest trailing its funnel. See where this funnel is tending and run the other way. All tornadoes progress from the southwest to the northeast. Bad as they are, this makes them far less terrifying than if they whipped back and forth over a town or chased you around the pasture. If you happen to be in the house, take to the cellar, the southwest corner of it. If you can't escape lie face down to the ground.

The only tornado that I have ever witnessed was an undeveloped one in England, and a bit lethargic compared to those of the Prairie States. But even this blew an entire train off the track. It had all the other appurtenances of a tornado, the hail, the twisted trees, the narrow southwest to northeast path. The fact that the houses had only corners of their roofs blown off showed that as a tornado it was distinctly second-grade and without power to explode.

England, shortly after, was raided by three water-spouts. These phenomena are caused by precisely the same conditions as are the tornadoes. They form over the sea, and the funnel is composed of water. They take considerable bodies of water up into the skies and torrential rains result over adjacent districts. If I remember correctly, two of the English water-spouts broke against the cliffs and the other, moving inland in modified form, gave Gloucester a nine-inch rain. Ships have been known to fire cannon at these spouts. If one hit a boat directly damage might be caused, but they have little of the destructive force of the tornado.

As our country builds up the destruction from this most powerful of all phenomena is likely to increase. Bureau warnings over phones may result in the saving of some lives; cellars will undoubtedly be built in the principal zones. But the problem is an interesting one, for unlike the waterspout, cannon cannot be employed to shatter an emptiness that stalks the more malignantly the emptier it is.

THE HURRICANE

The tropical hurricane is undoubtedly nature's mightiest exhibit. The hurricane is the cyclone par excellence. It does not differ from our ordinary weekly cyclone in the essentials of wind rotation or pressures or rainfall; but it does differ in place of birth, in its course, and chiefly in its intensity.

The genuine hurricane is a West Indian production. It is generally cradled in those islands south and east of Jamaica and Cuba. It is nursed by the trade-winds. The first notice of its birth is an alteration in these winds, which are among the most regular observances on our planet. An extensive formation of cirrus clouds spreads over the sky and the barometer, which has been stationary for some days, edges off and begins a long and gradual fall. Great rollers are noticed for a day or two before the winds rise. A hurricane moves slowly.

This tropical organization is superior in depth to our shallow, disc-like, continental cyclone which is one and rarely over two miles thick. The hurricane rears its head three, four, and even five miles high. Instead, too, of dissipating its force over thousands of miles at once it is only a few hundred miles in diameter. Its center moves methodically along at the not very impressive speed of fifteen miles an hour, while our cyclones hurry along at thirty. But the hurricane is thorough. The wind about its center reaches a velocity of 120 miles an hour. This velocity has never yet been attained on the surface of the earth by our trans-continental cyclone.

Our cyclone always has an eastward trend; the hurricane has a parabolic course. It begins by moving west on the trades, drifting and dealing destruction to the banana and sugar plantations of Jamaica. It enters the Gulf of Mexico, and since it is then pretty much out of the influence of the trades it curves to the right and begins to act like any other storm by heading directly for the St. Lawrence. If it passes out through the Florida straits it never reaches the St. Lawrence but speeds up the coast and out to sea, usually at Hatteras to follow the shipping routes across the North Atlantic.

But if it has become so involved in the Gulf of Mexico that it cannot escape to sea again, it comes up through the Gulf States and on toward New England. Fortunately as it goes inland its intensity diminishes because it has not so much energy-giving moisture to draw from. Also its sphere of action widens, its embrace is less mighty, its characteristics more those of an ordinary continental cyclone. It manages, however, to deliver gales of 80 miles an hour along the coastal plain, increasing to 100 at the exposed places such as Hatteras and Block Island.

The intensest hours of a hurricane are those when its course is changing from westward to eastward. Enormous rainfalls accompany these storms, amounting to six inches in some instances. Since one inch of rain amounts to 100 tons per acre, and 64,000 tons to a square mile one can imagine the great amount of evaporation that has taken place to so saturate the air as to drench vast territories to such an extent.

While scarcely a year goes by without one of these West Indian hurricanes distinguishing itself on our shores the one that visited Galveston in 1904 eclipsed all. It chose to turn in the vicinity of the city. The gale increased to over 100 miles an hour and the wind gauge then blew away. The waters of the Bay were heaped up and three thousand lives were lost in the flood and wreck of flying houses. This peculiar storm did not turn northeast at once but ascended the Mississippi, turning at the Lakes and proceeding down the St. Lawrence after having spent a week in our country.

The listless doldrums have sent us 121 of these storms in the last generation. June has seen 8, July 5, August 28, September 40, and October 40.

Sea-yarners have seized upon the hurricane to energize many a flagging chapter, and particularly have they emphasized the eye of the storm. The eye is that vortex where contending winds neutralize each other into a calm, where the sun shines out through the scud, where the waves, relieved of the great pressure, leap upward in wild disorder. Then the center passes and the wind flings itself upon the unlucky bark from the opposite quarter. Its first onslaught is always represented as being the fiercest of the whole storm and gradually lessening as the center drives farther away. This is true in the same way that the first attack of the thunderstorm is usually the fiercest, both being when the pressure begins to rise. This savage change to the northwest is naturally the hardest of all for the ships to bear as they must steady at once against the severest blast instead of gradually bracing for its culmination. In no department of meteorology has fiction adhered so closely to the facts as in the sea-rover accounts of the hurricane.

But in real life there is very little excuse for the vessel to be caught anywhere near the disastrous center of the storm. Indeed, for generations sea-captains have known how to escape the deadly eye. By watching the barometer and noticing in which direction the wind is working round they can tell the course to a nicety and estimate its speed. Then the wise ones run the other way for even the _Olympics_ and _Imperators_ of the sea are cowed by the might of the West Indian.

The typhoons of the West Pacific are similar manifestations.

The hurricane moves off from its birthplace so slowly that our Weather Bureau has an opportunity to size it up, to chart its probable course, and to warn shipping interests. The ship-owners, as a class, appreciate the service of the Bureau and obey its warnings. Vessels with cargoes of a total value of $30,000,000 were known to have been detained in port on the Atlantic coast by the Bureau's warnings of a single hurricane. Now that a much vaster commerce will steam through these dangerous waters toward the Panama Canal the warnings will assume an even greater importance.

The best description of a hurricane that it has been my fortune to read is in a story entitled "Chita," one of the remarkable fictions of Lafcadio Hearn. As truthfully as a scientist and with great beauty of style he has pictured the long days of burning sun, the foreboding calm, the thickening haze, the ominous increasing swell of the ocean, a breathless night with the lightning glowing from between piling towers of cloud, the startling suddenness of the wind's attack, its fury, the hissing rain, the shrill crescendo of the gale.

CLOUDBURST

It is the American tendency to exaggerate. We call every snowstorm a blizzard, every breeze a gale, every shower a cloudburst. In our generous vocabulary it never rains but it pours. Consequently if we, in the East, ever had a real blizzard or a real cloudburst we should be at a considerable loss to find words for an unprofane description. I do not know how they manage out West where these things occur.

A genuine cloudburst must be an amazing spectacle. It is caused by a furious updraft of wind keeping a rainstorm in suspense until so much water has accumulated that it has to let go all at once and the accumulation descends like a wet blanket.

This phenomenon is staged in the mountains; most often in the Rockies where melting snow and desert-hot ravines provide the necessary extremes of temperature. Wind blowing up a mountain-side can maintain considerable force,--so much that a man cannot possibly walk against it. Black thunder clouds brew on the peaks. Suddenly the collapse, and the person who tells the story afterward finds himself struggling in a torrent that a minute before had been a dry gulch. The moral of the story seems to be that if you are camping in the mountains and there is a strong upstream wind blowing and the clouds darken about the hill-tops and the thunder mumbles then don't make your bed in the creek-bottom lands. The high water marks of former freshets, but not of cloudbursts, show on the side of the stream.

Even in the less impulsive East a couple of inches of rain make a surprising rise in a little creek.

THE HALO

The halo is a luminous circle around the moon or the sun. It is caused by the refraction of light passing through moisture, which at the usual height is in the form of ice-crystals. The halo when complete consists of two large circles whose diameters are constant, 45 and 92 degrees. Then there are often other arches in contact. At each point of contact occurs a parhelion which is a mock sun of brilliant colors and called a sun-dog. Since the sun-dog is brighter than the other parts of the halo it sometimes appears when the rest of the halo cannot be seen. Sun-dogs hunt in pairs or fours. If the halo is colored the red is on the inside. When the colors are caused by diffraction instead of refraction, the red is on the outside of the prismatic ring and the halo is called a corona.

Having now satisfied the demands of science all that can be forgotten except that the halo around either sun or moon means excess moisture in the atmosphere. The wide halos are seen in the high cirrus clouds 25, 36, 48 hours in advance of a cyclone. At first the ring is very wide and faint with several stars in it. If the storm is advancing rapidly the halo brightens and narrows and the stars fade. This is proof to show that the proverb stating that the number of stars inside the ring is a forecast of the number of days of storm is sheer nonsense. For presently the ring closes and the stars disappear which would show according to the proverb that the storm had changed its mind and would cut down the number of days from several to none.

The moon grows paler. The light that it casts upon the earth is eerie at this stage. Within a few hours the cocoon of mist is completely woven about the moon. The circle has closed. Snow or rain begins within a few hours after the moon has entirely disappeared. If it does not so begin it shows that the process of increasing humidity is a very slow one and the storm center is probably passing far to one side of the observer. Also if the snow begins before the light of the moon is entirely suppressed the disturbance is a shallow one and the storm will be light.

When the halo is actually a corona (red outside) the approach of the storm can be gauged by the rapidity with which the circle grows smaller. For a decrease in diameter denotes that the size of the moisture drops is increasing and therefore the storm is approaching. As a matter of fact the corona will have disappeared long before the time for rain. Still it is useful to know that if the corona increases in size the conditions are clearing. With the halo the reverse holds. For when the clouds are very high the halo looks small, and high clouds imply swifter winds and a greater distance from the storm center.

The Zuni Indians who have an eye for the picturesque as well as for the truth state the chief fact about haloes happily: "When the sun is in his house it will rain soon." Another saying of theirs anent cumulus clouds holds for our country as well as for theirs: "When the clouds rise in terraces of white, soon will the country of the corn-priests be pierced with the arrows of rain."

There are many little observations which the man who has kept the corner of his eye open may profit by and yet which are rather difficult to express in type. Who could describe an egg for instance whose springtide of youth was far behind and yet was not quite ready for the discard! In nature it is the fleeting moment of transition, the half-tones of the border that are so hard to catch, so difficult to portray, and yet so very important not to miss if one is to become sure. There follow some of the baldest and most communicable half-facts about the weather that should be used oftener to bolster up some opinion gleaned from more positive sources than to mould one in their own strength.

Moisture in the atmosphere helps sight to a certain extent. For when the air is full of moisture its temperature tends to become equalized, obliterating irregularities which would otherwise reflect the vibrations producing sight and sound. So if one hears better or sees better on a certain day it augurs a moister atmosphere,--an auxiliary sign if there is a view that you are fond of looking at many times a day. In the city, alas, clearer vision on one day than another means merely that less coal is being used. But in camp there is very often a perceptible difference in one's seeing ability even on days that could all be classed as clear.

Another thing that the haunter of the woods may notice is that his smelling capacity is increased before a storm. The increase of humidity which precedes a rain buoys up odors and depresses smoke. Even in dry weather if you will stroll by a marsh you will notice how rank the vegetation smells and how the smells float in layers in the air strata of different humidity. One's sense of smell is a very slender thread on which to hang a storm, however.

Fires burn more briskly in dry air than in moist, but to tell the difference (if you can't feel it) you must be very sure that your wood is as dry on one day as on another.

Before a rain many plants close their flowers or shift their leaves. The dandelion, pimpernel, red clover, silver maple are good examples of this, but they would not be of much use in the North Woods. The closing, too, takes place only a few hours before rain and is merely confirmation of the signals rendered more adequately by clouds and winds.

Bugs and flies are particularly annoying before a storm and it is surprising that the spider should not take advantage of this to get a meal. But spiders are cautious and they never spin a web on the grass, at least on the day that brings a storm. The insects do not fly so high on these weather-breeding days and consequently the birds that feed on them fly lower. The chimney swifts are a particularly good guide to the different altitudes at which insects fly.