Part 2

A _chinook_ is a warm, dry wind that descends the eastern slope of the Rocky Mountains in Montana, Wyoming and Colorado, and flows north-eastward over the plains. Its effects are most pronounced in winter, when it brings about a very sudden rise in the temperature--in extreme cases as much as forty degrees in fifteen minutes! It causes snow to vanish as if by magic, and is appropriately nicknamed the "snow-eater."

"_Cloudburst_" is merely a picturesque name for a very heavy shower; usually a thunder-shower.

_West India hurricanes_ occasionally visit the United States, especially in the late summer and early autumn. These storms begin as violent cyclones of small extent (300 to 600 miles in diameter), usually somewhere east of the West Indies, sweep in a long curve across the Caribbean Sea, and then turn north, either passing up along the Atlantic Coast or crossing the Gulf of Mexico into the southern United States. Soon after entering the temperate zone they increase in size and diminish in violence, but are still vigorous enough on reaching the Gulf or South Atlantic Coast to cause great devastation. Low-lying shores are often inundated by the immense waves they generate.

_Cold waves_ are the rapid and severe falls in temperature that sometimes occur in winter, especially at the front of an anticyclone. Warnings of these occurrences, issued by the Weather Bureau twenty-four to thirty-six hours in advance, often result in the saving of millions of dollars' worth of merchandise susceptible to damage by freezing.

_Frosts_ in the spring and autumn are also predicted with great success, to the immense advantage of farmers, market-gardeners, and horticulturists. The practice of smudging or heating orchards, now so widespread, is usually carried on under the advice of the Weather Bureau, which gives prompt notice to the orchardist when such precautions are in order. The bureau publishes charts showing the average and extreme dates of the last frost in spring and the first frost in autumn for all parts of the country.

A _fog_ is a cloud resting on the surface of the earth. In the United States fog is commonest along the northern and middle parts of the Atlantic and Pacific Coasts. In the interior of the country, especially the western part, it is of rare occurrence, the average number of days a year with fog being less than ten.

Lastly--weather fallacies are rife. _Indian summer_ is merely a type of mild, hazy, heavenly weather that prevails intermittently during our long American autumns. The _equinoctial storm_ is a myth; the climate has not "changed" anywhere within the span of a human lifetime (one year differs from another, but there is no progressive or permanent change); and the _moon_ has nothing whatever to do with THE WEATHER.

SUPPLEMENTARY READING

CLIMATE AND WEATHER _By H. N. Dickson_

AMERICAN WEATHER _By A. W. Greely_

WEATHER SCIENCE _By R. G. K. Lempfert_

SOME FACTS ABOUT THE WEATHER _By W. Marriott_ Second edition.

METEOROLOGY _By W. I. Milham_ The latest general textbook on the subject in English.

FORECASTING WEATHER _By W. N. Shaw_

ELEMENTARY METEOROLOGY _By F. Waldo_

Consult also the numerous publications of the United States Weather Bureau, which will be found in most public libraries.

*** Information concerning the above books and articles may be had on application to the Editor of The Mentor.

THE OPEN LETTER

"What is lightning and what causes it?" The question came to us a few days after we had made announcement of a "Weather" number of The Mentor. It was a natural question, for lightning is the most sensational of all weather phenomena. It has always had a fearful sort of fascination for humanity. To the ancients it came as a bolt of wrath from the hand of Jove. To the fire-worshipers it was a warning message. To parched travelers it was a bright promise, for it heralded the coming of rain. To the superstitious it was a signal flash from the spirit world. And to those of nervous temperament it was a highly disturbing phenomenon producing emotions varying from uneasiness and alarm to hysteria. The question then, "What is lightning and what causes it?" has an interest for all. I referred it to Mr. Talman, the author of the Mentor article on "The Weather." His reply follows.

* * * * *

"Not so many generations ago 'natural philosophers' thought that inflammable gases, exhaled from the earth, took fire spontaneously in the air, and that this was lightning. The idea also prevailed--and it is not yet quite extinct--that a stroke of lightning involved the hurling down from the sky of a mass of rock, called a 'thunderbolt.' In the eighteenth century people became quite familiar with the process of generating, by friction, a mysterious something called 'electricity,' which, when it passed from one body to another through a small layer of intervening air, produced sparks. Several philosophers noticed the resemblance between these sparks and lightning. It remained, however, for Benjamin Franklin to prove that lightning was really an electrical discharge on a large scale. The experiments by which he proposed to demonstrate this were successfully performed, first by others, in France, and then, by Franklin himself, at Philadelphia. With the aid of his famous kite he drew down from a thundercloud a little of the 'electrical fluid' (as it was then called), and produced tiny sparks from an iron key at the lower end of the wet kite-string.

"We do not even yet know what electricity is, but we know a great deal about the way it behaves and the effects it produces. There are two kinds of electricity, which we call _positive_ and _negative_. A body is said to be _charged_ when it has an excess of either kind, and the two kinds have a tendency to unite and neutralize each other's effects. Thunderclouds become heavily charged with electricity. We are not quite sure how this happens, but it is now commonly believed that the strong uprising currents of air that occur in the storm, in the process of breaking up the water-drops in the cloud also separate positive from negative electricity; leaving the former in excess in the part of the cloud next to the earth, and carrying the latter far aloft.

"By a process called 'induction' the positive charge in the cloud draws an excess of negative electricity to the surface of the ground underneath. The stronger the contrast between these opposite charges, the harder they try to break through the interposing barrier of the air (which is a poor conductor of electricity) and to neutralize each other. At length they succeed in doing so. A powerful stream of electricity flows for an instant between cloud and earth. Its passage heats the air and makes it luminous--just as the passage of an electric current heats the filament of an electric lamp and makes it luminous. This is lightning.

"These discharges occur not only between the clouds and the earth, but also, and probably more often, between clouds charged with opposite kinds of electricity.

"The sudden expansion of the heated air along the path of the discharge affects our ears just as does the sudden expansion of the air at the mouth of a gun when it is fired. In each case a wave is sent through the air in all directions from the place of disturbance, and our ear-drums are set in vibration. That is thunder."

* * * * *

Take courage then, you timid ones, who wince in the lightning's flash and tremble under the thunder's roll. Thunder is simply a vibration of your ear drums--and, when you hear the thunder, be assured, all danger is over.

[Signature: W. D. Moffat]

EDITOR

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1. Beautiful Children in Art 2. Makers of American Poetry 3. Washington, the Capital 4. Beautiful Women in Art 5. Romantic Ireland 6. Masters of Music 7. Natural Wonders of America 8. Pictures We Love to Live With 9. The Conquest of the Peaks 10. Scotland, the Land of Song and Scenery 11. Cherubs in Art 12. Statues With a Story 13. Story of America in Pictures: The Discoverers 14. London 15. The Story of Panama 16. American Birds of Beauty 17. Dutch Masterpieces 18. Paris, the Incomparable 19. Flowers of Decoration 20. Makers of American Humor 21. American Sea Painters 22. Story of America in Pictures: The Explorers 23. Sporting Vacations 24. Switzerland: The Land of Scenic Splendors 25. American Novelists 26. American Landscape Painters 27. Venice, the Island City 28. The Wife in Art 29. Great American Inventors 30. Furniture and Its Makers 31. Spain and Gibraltar 32. Historic Spots of America 33. Beautiful Buildings of the World 34. Game Birds of America 35. Story of America in Pictures: The Contest for North America 36. Famous American Sculptors 37. The Conquest of the Poles 38. Napoleon 39. The Mediterranean 40. Angels in Art 41. Famous Composers 42. Egypt, the Land of Mystery 43. Story of America in Pictures: The Revolution 44. Famous English Poets 45. Makers of American Art 46. The Ruins of Rome 47. Makers of Modern Opera 48. Durer and Holbein 49. Vienna, the Queen City 50. Ancient Athens 51. The Barbizon Painters 52. Abraham Lincoln 53. George Washington 54. Mexico 55. Famous American Women Painters 56. The Conquest of the Air 57. Court Painters of France 58. Holland 59. Our Feathered Friends 60. Glacier National Park 61. Michelangelo 62. American Colonial Furniture 63. American Wild Flowers 64. Gothic Architecture 65. The Story of the Rhine 66. Shakespeare 67. American Mural Painters 68. Celebrated Animal Characters 69. Japan 70. The Story of the French Revolution 71. Rugs and Rug Making 72. Alaska 73. Charles Dickens 74. Grecian Masterpieces 75. Fathers of the Constitution 76. Masters of the Piano 77. American Historic Homes 78. Beauty Spots of India 79. Etchers and Etching 80. Oliver Cromwell 81. China 82. Favorite Trees 83. Yellowstone National Park 84. Famous Women Writers of England 85. Painters of Western Life 86. China and Pottery of Our Forefathers 87. The Story of The American Railroad 88. Butterflies 89. The Philippines 90. Great Galleries of the World: The Louvre 91. William M. Thackeray 92. Grand Canyon of Arizona 93. Architecture in American Country Homes 94. The Story of The Danube 95. Animals in Art 96. The Holy Land 97. John Milton 98. Joan Of Arc 99. Furniture of the Revolutionary Period 100. The Ring of the Nibelung 101. The Golden Age of Greece 102. Chinese Rugs 103. The War of 1812 104. Great Galleries of the World: The National Gallery, London 105. Masters of the Violin 106. American Pioneer Prose Writers 107. Old Silver 108. Shakespeare's Country 109. Historic Gardens of New England

NUMBERS TO FOLLOW

July 15. AMERICAN POETS OF THE SOIL. _By Burges Johnson, Associate Professor of Literature, Vassar College._

August 1. ARGENTINA. _By E. M. Newman, Lecturer and Traveler._

* * * * *

WEATHER SERVICES AT HOME AND ABROAD

Monograph Number One in The Mentor Reading Course

Posted up in public offices, in hotel corridors, and other conspicuous places in our cities, the official weather map is a familiar sight. Even more familiar is the official weather forecast, displayed, as a rule, on the first page of the daily newspaper, and sent broadcast over the country on the little brown cards which one may see in the village postoffice as well as in the city drug-store. When a great storm sweeps over land or sea, detailed official reports concerning its progress and characteristics are published in the daily press. When a lawsuit involves a dispute as to the temperature or the state of the sky on a certain day, the official weather records are consulted.

How much do you know about the branch of the national government that is charged with the duty of keeping watch of the weather--recording its vagaries as they occur, and also predicting them, as far as is humanly possible?

Besides its office in Washington, where more than two hundred persons are constantly employed, the Weather Bureau has about two hundred stations, manned by professional meteorologists and observers. One of these will be found in almost every large city, while some are in towns of very modest importance. A regular Weather Bureau station is well worth a visit. The instrumental equipment of these stations is almost superhuman in the accuracy with which it sets down on paper the chronicle of weather happenings from day to day and from moment to moment. Little less marvelous is the system by means of which weather information--past, present and future--is disseminated from these official foci. The postoffice, the telephone, the telegraph (wire and wireless) are all pressed into service to the fullest extent--especially in giving timely notice of approaching storms and other destructive forms of weather. These agencies are supplemented by visible and audible signals, in the shape of flags, lanterns, railway whistles and so forth.

Contrary to popular belief, the Weather Bureau does not exist primarily for the purpose of telling the public (with a considerable margin of uncertainty) whether it will be advisable, on the morrow, to carry an umbrella or wear an overcoat. The important work of the Bureau is twofold. It consists, first, in the prediction of those atmospheric visitations, such as storms, floods, and cold waves, which endanger life and property on a large scale; and, second, in the maintenance of the records that form the basis of climatic statistics. In both these directions the Bureau splendidly justifies its existence.

Our national weather service was founded in 1870, and for twenty years was maintained by the Signal Corps of the Army. In 1890 it was established on the present basis, as the Weather Bureau of the Department of Agriculture.

Most civilized countries possess official services for the observation and prediction of weather, though no other is organized on quite so grandiose a scale as ours. The British Meteorological Office, the Prussian Meteorological Institute, the Central Meteorological Bureau of France, and the Central Physical Observatory of Petrograd are among the leading institutions of this character in the Old World. Admirable weather services also exist in India, Japan, Australia, Canada, Argentina and elsewhere.

METEOROLOGICAL INSTRUMENTS

Monograph Number Two in The Mentor Reading Course

The history of meteorological instruments dates back at least as far as the fourth century before the Christian era, when the depth of rainfall was measured in India by some form of gauge. We again hear of rain-gauges being used in Palestine in the first century of the present era. Thermometers with fixed scales were used in Italy in the seventeenth century, and the great Galileo, born in Pisa in 1564, took part in perfecting these instruments. Wind-vanes were known to the ancients. The earliest one of which we have any record surmounted the famous Tower of the Winds at Athens. In the Middle Ages the weathercock became the usual adornment of church steeples. The barometer was invented by Torricelli in 1643.

Most meteorological instruments, however, are of quite recent origin, and this is true especially of these types of apparatus that make automatic records, thus replacing, to a large extent, the human observer.

Our picture on the other side of this sheet shows the instruments used by the "co-operative" observers of the Weather Bureau. These observers, of whom there are about 4,500, well distributed over the country, serve the government without pay, and their painstaking observations have alone made possible a detailed survey of our climate. In the picture we see, on the right, an ordinary rain-gauge, and, on the left, a thermometer-screen containing two thermometers; viz., a maximum thermometer, for recording the highest temperature of the day, and a minimum thermometer, for recording the lowest. The screen, which is of wood, painted white, serves to shield the instruments from the rays of the sun, while permitting free ventilation. Under these conditions the thermometers show the temperature of the _air_; whereas when exposed to direct sunlight a thermometer shows the temperature acquired by the instrument itself, and this may differ materially from the air temperature.

In contrast to this simple equipment, we find at a regular meteorological station, or observatory, an impressive collection of apparatus for observing and recording nearly all the elements of weather. The pressure of the air is measured by the mercurial barometer, and registered continuously by the barograph; the temperature of the air is automatically recorded by the thermograph. Other self-registering instruments maintain continuous records of the force and direction of the wind, the amount and duration of rainfall, the duration of sunshine, the humidity of the air, etc. There are also instruments for measuring evaporation, the height and movement of clouds, the intensity of solar radiation, the elements of atmospheric electricity, and various other phenomena of the atmosphere.

CLOUDS AND RAINFALL

Monograph Number Three in The Mentor Reading Course