ELEMENTS OP METEOKOLOGY, WITH QUESTIONS FOR EXAMINATION, DESIGNED FOR SCHOOLS AND ACADEMIES. BY JOHN B^OCKLESBY, A.M., of Mathematics and Natural Philosophy in Trinity College, Hartfoid. See page 151. ILLUSTRATED WITH ENGRAVINGS. TENTH BEVISED AND^ENI^BGED EDITION. "Fire and hail; snow apd vapor; Stomy wind ftumta Hfij word." NEW YORK: SHELDON AND COMPANY, PUBLISHERS, STREET, 1878. Entered according to Act of Congress, in the year 1848, by JOHN BROCKLESBY, In the Clerk's Office of the District Court of Connecticut. CASE, LOCKWOOD & CO., ELECTROTYPES AttD PRJNJTEHS, HARTFORD, CONW. PREFACE. METEOROLOGY is a subject of interest to all. We in the very midst of its phenomena, and are constantly subjected to their influence. Many of the singular pro- cesses of nature which this science unfolds, are intimate- ly connected with our being and happiness, while others, on account of their beauty and sublimity, fill the mind with admiration and awe. The subject being one of universal interest, we might naturally suppose it to be universally understood ; but such is not the case. Meteorology, as a science, is of recent origin ; for it is only within the space of a very few years that it has risen, through the efforts of many gifted minds, to the rank it deserves to hold amid the various departments of knowledge. Meteorology is a portion of Natural Philosophy, and in the colleges of our land, lectures upon this subject form a part of the regular academical course ; but no similar system prevails in our High Schools and Acade- mies. Nor is it to be expected ; since, with the present want of facilities for obtaining information, the teacher would be obliged to devote an undue share of his time to the acquisition of the knowledge requisite for this object. Neither can a text-book be procured; for the author is not aware that any distinct treatise on this science is extant in the English language, except the 3 G 9246 IV PREFACE. translation from the German of Kaemtz's " Complete Course of Meteorology ;" a work which, though exceed- ingly valuable to the advanced student, is not suitable for a text-book on account of its size, expense, and mode of execution. The present little work has therefore been prepared, not with the view of adding one more to the long list of studies now pursued in our academical institutions ; but for the purpose of bringing into general notice a rich but hitherto comparatively unknown field, within the do- mains of natural science. The author has therefore endeavored, while retaining all the important principles of Meteorology, to condense the subject as much as possible, in order that this ele- mentary treatise may be studied in connection with Nat- ural Philosophy, without consuming too much time. In regard to facts, they have been sought wherever it was supposed they could be found, and reference has been made in nearly all cases to the authorities whence they were taken. Should it be required a more extended treatise may be expected, adapted to the wants of students in colleges. HARTFORD, July 7th, 1848. REFERENCES. (C. 957), for example, denotes Comstock's Philosophy, Article 957, (last edition. (Art 132), for example, denotes Article 132 of this work. TABLE OF CONTENTS. PREFACE 5 Subject defined 13 PART I. OF THE ATMOSPHERE. Barometer 14 Temperature 18 Capillarity 18 Pressure of the Atmosphere 19 Variations in Latitude 19 Variations in Altitude 21 Density of the Atmosphere 22 Weight of the Atmosphere 24 Temperature of the Atmosphere 24 Thermometer 25 Self-registering Thermometer 27 Mean Daily Temperature 29 Variations of Temperature in Latitude 30 Variations of Temperature in Altitude 30 Humidity of the Atmosphere 32 Absolute Humidity 33 Relative Humidity 33 Hygrometer 34 Height of the Atmosphere 36 PART II. AERIAL, PHENOMENA. CHAPTER I. OP WINDS IN GENERAL. Cause of Wind 38 Velocity 39 Anemometer 40 Force of Winds 40 Trade Winds 41 Origin 41 Limits of the Trade Winds 43 Calms 44 Winds of the Higher Latitudes 45 Upper Westerly Wind of the Tropics 48 Periodical Winds 48 Monsoons 48 Origin 49 Land and Sea Breezes 50 Origin 50 Variable Winds 51 Physical Nature of Winds ,. 52 Puna Winds 52 Simoom &4 Sirocco ,,,, , 54 VI CONTENTS. CHAPTER II. OF HURRICANES. p^^ Hurricanes defined .54 Path of the Storm 5G Velocity 56 Diameter 57 Examples 57 Fall of the Barometer 58 Circuit Sailing 60 Axis of the Hurricane 61 Espy's Theory 62 CHAPTER III. OF TORNADOES OR WHIRLWINDS. Facts 63 Origin 65 Whirlwinds excited by Fires 65 Results of Centrifugal Action 66 Effects of Expansion 67 CHAPTER IV. OF WATER-SPOUTS. Water-spouts defined 68 Dimensions 71 Popular Error 73 Sand Pillars 72 Beneficial Effects of Winds 73 PAUT III. AQUEOUS PHENOMENA. CHAPTER I. , OF RAIN. Cause of Rain 74 Rain Gauge 75 Distribution of Rain in Latitude 75 Exceptions 76 Days of Rain 77 Distribution in Altitude 77 Rain upon Coasts 78 Rains within the Tropics 79 Rainy Seasons 79 Cause 80 Periodical Rains of India 80 Periodical Rains of Congo 81 Rains in the Higher Latitudes 82 Rainy Winds 82 Regions without Rain 83 Egypt 83 Peru 84 Constant Rains 84 Excessive Showers. , 85 Rain without Clouds 85 Cause ..86 CONTENTS. VH CHAPTER II. OP POOS. Page Fogs defined 8(? Constitution 87 Distribution in Latitude . . . . 87 Tropical Regions 87 Temperate Regions 87 Polar Regions , 87 Cause 88 Local Distribution 88 Rivers 89 Mountains 90 Capes 91 Shoals 91 Newfoundland 91 England 91 Garuas 92 CHAPTER III. OP CLOUDS. Clouds defined 94 Strata of Clouds 95 Thickness 96 Height 96 Clouds on Mountains 97 Classification 99 Cirrus 99 Cumulus 100 Stratus 102 Cirro-stratus 103 Cirro-cumulus 10J* Cumulo-stratus 104 Nimbus 105 CHAPTER IV. OP DEW. Dew defined 106 Deposition 106 Influence of Condition of the Atmosphere 107 Humidity 107 Serenity 107 Tranquillity 108 Evening and Morning 108 Influence of the Substance bedewed 109 Constitution 109 Surface and Form 109 Location 110 Color HI Observations Ill Facts Explained 112 Beneficent Distribution 112 CHAPTER V. OP HOA5.-FROST AND SNOV. Hoar-frost .... 113 Snow .. 115 I* Vili CONTENTS. Paftt Snow Flake 115 Snow Crystals 110 Natural Snow Balls 118 Red Snow 119 Green Snow 120 Cause 120 Uses of Snow 121 CHAPTER VI. OP HAIL. Hail 122 Structure 122 Size 122 Geographical Distribution 123 Origin 123 Volta's Theory 124 Olmsted's Theory 125 Curve of Perpetual Congelation. 125 Action of Opposite Currents 126 Action of Whirlwinds 128 Influence of High Mountains 129 Hail in Southern Inrtia 129 PART IV. ELECTRICAL PHENOMENA. CHAPTER I. OP ATMOSPHERIC ELECTRICITY. Electrometers 131 Electric Condition of the Atmosphere 133 Annual Variation in Intensity 133 Daily Variation 133 Variation in Altitude _ 134 Origin 135 Evaporation 135 Condensation 136 Vegetation 136 Combustion 136 Friction 137 CHAPTER II. OF THUNDER-STORMS. General Distribution 137 Origin 138 Electrical State of Thunder-clouds 139 Electric Action of Thunder-clouds 140 Return Stroke 140 Height of Thunder-storms 142 Lightning 143 Origin 143 Kinds 143 Zigzag-lightning 144 Sheet-lightning 144 Ball-lightning 144 Heat-lightning 145 Velocity of Lightning 146 Color 147 CONTENTS. Effects ^ Fulgurites 148 Volcanic Lightning 149 Thunder 150 Identity of Lightning and Electricity 150 Franklin's Experiment 151 Romas' Experiment 152 Richman's Death 152 Lightning Rod 153 Material 153 Size 153 Mode of Erection 153 Extent of Protection 154 Electric Fogs 155 Spontaneous Electricity 156 St. Elmo's Fire 156 Electric Rain, Hail and Snow 157 Electric Action upon Telegraphic Wires 158 PART V. OPTICAL PHENOMENA. CHAPTER I. OF THE COLOR OF THE ATMOSPHERE AND CLOUDS. Color of the Atmosphere 162 Cyanometer 162 Effect of Latitude 163 Effect of Altitude 164 Colors of Clouds 165 CHAPTER II. OF THE RAINBOW. Primary Bow 170 Secondary Bow 172 Breadth of the Bows 173 Position and Size of the Rainbow 174 Rainbows in the North 175 Extraordinary Bows 175 Supernumerary Bows 176 Lunar Bows 176 CHAPTER III. OF MIRAGE. Instances 179 Fata Morgana 181 Origin 183 Erect and Inverted Images above the Object 183 Magnified Images 185 Images below the Object 1 87 Images produced by Reflection 188 Spectre of the Brocken 190 Artificial Mirage 191 CHAPTER IV. OF CORONAS AND HALOES. Coronas 192 Origin... 193 X CONTENTS. Anthelia 19*7 Haloes 199 Facts 199 Ordinary Halo of 45 201 Extraordinary Halo of 90 203 Circles passing through the Sun 203 Parhelia and Paraselenae 205 PAKT VI. LUMINOUS PHENOMENA. CHAPTER I. OF METEORITES. *acts 206 Size of Meteorites 208 Altitude 208 Velocity 209 Aercii tes 209 Form 209 Composition * . . 210 Meteoric Iron 211 Origin of Meteorites 212 First Hypothesis 212 Second Hypothesis 213 Third Hypothesis 213 Fourth Hypothesis 214 Fifth Hypothesis 21G CHAPTER II. OF SHOOTING-STARS AND METEORIC SHOWERS. Altitude 216 Velocity 217 Course 218 Magnitude 218 Splendor 219 Meteoric Showers 220 November Epoch 220 Varieties 221 August Epoch 222 Origin 224 Chaldni's Hypothesis 225 CHAPTER III. OF THE AURORA BOREALIS OR NORTHERN LIGHT. Constitution 22b Dark Segment 226 Arch of Light 228 Streamers 230 Color 230 Corona. 230 Extent 232 height 233 Sounds attending the Aurora 234 Time 235 Frequency 236 Disturbance of the Magnetic Needle 237 Cause 239 Utility 24C CONTENTS. XI PART VII. MISCELLANEOUS PHENOMENA. CHAPTER I. 67 THE PALL OP TERRESTRIAL SUBSTANCES FOREIGN TO THE ATMOSPHERE. Page dust-storms and Blood-rains 241 Dust-storms 242 Instances 242 Blood-rains 245 Instances 245 Black Rain . 247 Red Hail .248 Black Hail 248 Storms of Colored Snow 248 Red Snow 248 Black Snow 249 Nature of the Dust 249 Infusoria 250 Structure 250 The Italian Dust-shower of 1803, and the Calabrian of 1813 251 Atlantic and Cape de Verd Dust 251 Sirocco Dust 253 Number of Distinct Organisms Discovered 256 Number and Extent of Dust-storms and Blood-rains 266 Their Periodicity 257 Origin of the Dust 257 Volcanic Showers 259 Cause 259 Instances Jorullo 259 Souffriere 259 Toniboro 260 Cosiguina 261 Yellow Rains Pollen-rains 262 Gossamer-shower 262 CHAPTER II. DRY FOG AND INDIAN-SUMMER HAZE. Dry Fog 264 Instances 265 Cause 266 Indian-summer Haze >b Cause S 68 METEOROLOGY. 1. METEOROLOGY is THAT BRANCH OF NATURAL SCIENCE WHICH TREATS OF THE ATMOSPHERE AND ITS PHENOMENA. The subject may be properly divided into six parts. 2. PART I. THE ATMOSPHERE. PART II. AERIAL PHENOMENA comprehend- ing Winds in general, Hurricanes, Tornadoes, and, Water-spouts. PART III. AQUEOUS PHENOMENA including Rain, Fogs, Clouds, Dew, Hoar-frost and Snow, and Hail. PART IV. ELECTRICAL PHENOMENA com- prising Atmospheric Electricity and Thunder-storms. PART V. OPTICAL PHENOMENA including the Color of the Atmosphere and Clouds, Rainbow^ Mirage, Coronas, and Haloes. PART VI. LUMINOUS PHENOMENA embra- cing Meteorites, Shooting Stars and Meteoric Showers, and the Aurora Borealis. PART VII. MISCELLANEOUS PHENOME- NA including the Fall of Terrestrial Substances foreign to the Atmosphere, and Dry Fog and Indian Summer Haze. What is Meteorology ? Into how many parts is it divided ? Rehearse the several parts with their subjects. PART I. OF THE ATMOSPHERE. 3. As the common properties of the air, viz., weight, fluidity and elasticity, are supposed to be already known, C. 502,) we shall proceed at once to the discussion of the entire body of air, termed the atmosphere ; and first of its pressure, which is ascertained by the barometer, an instrument so called from the Greek words, baros, weight, and metron, measure. BAROMETER. 4. This instrument is of the highest importance in Meteorology, and requires a minute description. It is thus constructed. Into a glass tube, about three feet in length, open at one end and closed at the other, mer cury is poured until it is full ; the open end being no closed by the finger, or any other means, the tube is i verted, and the lower end immersed in a vessel of me cury. When beneath the surface of the fluid the end is unstopped, and the column of mercury within the tube then settles down, until its summit is about thirty inch- es above the level of that within the vessel. The space above the column in the tube is a void, and is called the Torricellian vacuum, from Torricelli, the name of the Italian philosopher, who first constructed this instru- ment. 5. The column of mercury within the tube is sup- ported above the level of that in the vessel, by the up- ward pressure of a column of the atmosphere, having- the same base as itself. What is the atmosphere ? How is its pressure ascertained ? How is the barometer made ? What supports the column of mercury ? BAROMETER. 15 6. Thus, in fig. 1., the atmospheric column a a, of indefinite length, but of the same size as the barometric column Db, presses upon the mercury in the vessel. K, with a force equal to its own weight ; now since any force, acting upon a fluid, is communicated in every direction, this pressure will be transmitted through the mercury, in the direction of the arrows, and acts at D, within the tube, against the mercurial column Db. This upward force will be resisted at D, by the weight of Db, and the mercury will sink in the tube until the two pressures counterpoise each other, in exactly the same manner as two equal weights in the opposite scales of a balance. 7. From these considerations, it is man- ifest, that the weight of the atmospheric column a a is equal to that of the mercuri- al column, Db of the same base ; and this weight can be estimated in the following manner. If the base at D contains one square inch, the column Db, at its usual height, will contain, nearly, 30 cubic inches ; and since one cubic inch of mercury weighs 3426.76 grains, the weight of thirty will amount to 102802.8 grains. This product being now divided by 7004, the numbei of grains in a pound avoirdupois, the result will bo nearly 14.7 Ibs. ; a quantity equal to the weight of the barometric column, and consequently to the pressure of the atmosphere on every square inch of surface. 8. Any increase in the density of the atmosphere will be denoted by an elevation of the mercury, and a de- crease by its depression. The cause of this is obvious, in the first case, a a becomes heavier, and requires more BAROMETER. Explain Figure 1. How is the pressure of the atmosphere, on every square inch, computed 1 How does any change in the density of the air affect the height of the barometer ? 16 THE ATMOSPHERE. mercury to balance it ; therefore Db is lengthened. ID the second case, a a is lighter, and, as a less quantity of mercury will then balance it, Db is shortened. Such changes are constantly occurring, but are very minute, and, in order that they may be accurately indicated, the instrument must be made with the nicest care. 9. To secure a perfect instrument, it is essential that the mercury should be free from any solid impurities, else the summit of the column will either be above, or below, its proper level, according as the foreign matter, mixed with the mercury, is lighter, or heavier, than the fluid. This end is attained by straining the mercury through chamois leather. If it is amalgamated with zinc, or lead, it is purified by washing it with acetic, or sulphuric acid. 10. When the tube is filled, moisture and small bub- bles of air are found adhering to its interior surface, and are also contained in the mercury. These, if not expel! ed, will ascend when the tube is inverted into the Torri- cellian vacuum, the moisture rising in vapor. By their united elastic force, the ascent of the barometric column will be checked, whenever' any increase in the density of the atmosphere tends to elevate it. 11. This source of error is removed by boiling the mercury in the tube. When all the air and vapor are expelled, the tube, if gently struck, will give forth a dry, metallic sound ; but if a bubble of air remains, the sound will be dull and heavy. By connecting the open end of the tube with an air pump, during the process of boiling, Dr. Jackson, of Boston, has still more effectually removed this imperfection. 12. By these means, the air may perhaps be totally excluded, when the instrument is first constructed ; but in the course of time, it will again insinuate itself be tween the glass and the mercurial column. To pre- vent this evil, Prof. Daniell, of King's College, London, What precautions are adopted to secure a perfect barometer 7 How is the mercury purified, and why 1 How are moisture and air expelled from the tube, and why? What is Prof. Daniell's improvement? BAROMETER. 17 welds to the open end of the glass tube a ring of plati- num, which possesses a greater affinity for mercury than glass. The mercury adheres closely to the platinum, like water, and the passage of air, according to all ex- periments, appears thus to be effectually prevented. 13. Since the constant changes in the weight of the atmosphere produce corresponding fluctuations in the height of the barometer, a scale is placed near the top of the tube, extending from twenty-seven to thirty-one inches, a space, which includes, at the surface of the earth, all the fluctuations of the column. This scale is divided into tenths of an inch ; but, as the variations of the barometer are exceedingly minute, a contrivance, called a vernier, is annexed, by which a change, to the extent of one five hundredth of an inch, can be easily measured. 14. As the surface of the mercury, in the reservoir, is raised by the descent of the column, and depressed by its elevation, any change in the height of the barometer cannot be accurately estimated, while the scale remains in the same position ; unless this surface is always brought to the same point, before taking an observation. The necessity of so doing will be obvious, from the fol- lowing illustration. Suppose the surface of the mercury in the cistern K, figure 1., to be fifty square inches, while that of a hor- izontal section of the column is but one. Should the barometer sink one inch, the surface of the mercury in the cistern will rise one fiftieth of an inch, and the amount of the depression of the column, if measured from this surface, will be only forty-nine fiftieths of an inch, instead of one inch, its true depression. 15. The contrivance employed by Fortin, a celebrat- ed French artist, to remove this error, consists in ad- justing to the cistern K, fig. 1., a movable bottom, which can be elevated or depressed, by means of the screw What is the length of the barometric scale 1 How small a variation in height can be measured ? What is Fortin's contrivance, and for what purpase adopted 1 18 THE ATMOSPHERE. P, until the surface of the mercury shall just touch the fixed ivory index L, at its lower extremity ; which point is the zero of the scale, or the place from which the height of the barometer begins to be reckoned. 16. When, by adopting the previous precautions, the barometer has been so far perfected, two corrections are still necessary, before recording observations ; the Srst for temperature, and the second for capillarity. That of temperature depends upon the expansion of (he mercury and the scale ; the latter being partially corrective of the former, inasmuch as the divisions of measurement upon the scale, lengthen, at the same time, with the column of mercury. 17. TEMPERATURE. Mercury dilates, for every de- gree Fah. about one ten-thousandth part of its bulk, taken at the freezing point. The expansion of the scale varies with the metal of which it is composed, but its amount is, usually, so small, that it may safely be neg- lected in the required correction. Hence the following practical rule lias been adopted, for reducing any ob- served altitude of the barometer, to the corresponding altitude, at the freezing point. " Subtract the ten-thou- sandth part of the observed altitude, for every degree above the freezing point" Thus, if the barometer stands at 29 inches, and the thermometer at 52, the required correction is 20 X .0001 X 29 = 058. If the temperature is below 32, the correction must be added. To facilitate these calculations, a thermometer is always attached to the barometer. 18. CAPILLARITY. By capillary attraction is (C. 53,) understood, the force exerted by the interior surface of small tubes, upon the fluids contained within them. When the fluid moistens the tube, it rises above its pro- per level ; but when it does not, as in the case of mer- cury, it sinks below it. From this cause, a depression, termed its capillarity, occurs in the barometer, the extent How is the barometer affected by a change in temperature 1 Give the rule for reducing the height to the corresponding height at th freezing point. Why is capillarity a source of error ? PRESSURE OP 1HE ATMOSPHERE. 19 of which is dependent upon the size of the interior diam- eter of the tube, and a correction for this must be added to the apparent -height, in order to obtain the true alti- tude. In tubes of a small bore, the error from this source is considerable ; but when the diameter exceeds half an inch, it becomes so small, that it may safely be neglected. This will be rendered evident by the inspec- tion of the following table, which gives the amount of depression for tubes of various sizes. Diameter of tube. Depression. inches, inches. .10 1403 .20 0581 .40 0153 .50 0083 19. When the instrument is not stationary, but is carried from clime to clime, and to different heights above the sea-level, two other corrections are necessary ; one for the varying force of gravity, indifferent latitudes, and the other for the change of pressure, which dimin- ishes with every increase of altitude above the ocean. Such is the barometer, an instrument of great prac- tical use, and of the highest value in meteorological re- searches. PRESSURE OF THE ATMOSPHERE. 20. VARIATION IN LATITUDE. The mean or average pressure of the atmosphere, as indicated by the barom- eter, is found to be nearly the same in all latitudes, when every essential correction is made. It increases a little from the equator to about the 30th degree of latitude, where it is greatest ; it then decreases to nearly the 64th degree, where it is least ; after this it again increases, and between the 75th and 76th degrees, the pressure is equal to that of the equatorial climes. AH Is it greater in tubes of a small or large bore 7 When the barometer is portable, what other corrections are necessary ? What is said of the barometer ? In what manner does the pressure of the at mosphere vary in latitude 1 20 THE ATMOSPHERE. this is obvious from the following table, founded upon observations, where corrections are made for gravity, altitude above the sea-level, and temperature. PLACES. LATITUDE. HEIGHT OF BAROMETER. Cape of Good Hope, . Christianburg, . . . Tripoli, ..... 33 S. 5 30' N. 33 N. Inches. 29.955 29.796 30 127 Godthaab, .... Spitzbergen, . . . 64 N. 75 30' N. 29.598 29.801 21. The pressure of the atmosphere at any given spot is not invariable ; for the height of the barometer is perpetually changing throughout the year. The ex- tent of its fluctuations is, however, by no means the same in all places, being least at the equator ', and great est towards the poles. Thus its range within the tropics is but a little more than one-fourth of an inch ; at New York, 40 42' 40" N. lat., 2.265 inches, from the observa- tions of five years ; at St. Johns, Newfoundland, 47 34 X 3" N. lat., 2.54 inches, during the same period ; while in Great Britain it amounts to three inches. The greatest fluctuations occur between the 30th and 60th degrees ol latitude. 22. There is also a constant daily variation in the atmospheric pressure, for the barometer, as a general rule, falls from 10 o'clock, A. M. to 4, P. M. ; it then rises until 10, P. M., when it again begins to descend, reaching its lowest point at 4, A. M. ; from this time it rises, until it once more attains its highest elevation, at 10, A. M. These variations are exceedingly minute, and contrary to the annual range, are greatest at the equator, and decrease with the latitude ; disappearing about the parallel of 60. 23. This variation amounts at Give examples. Where are the annual fluctuations of the barometer least ? Where greatest ? Give examples. Describe the diurnal variations. Where greatest ? Where least 7 PRESSURE OF THE ATMOSPHERE. 21 PLACES. LATITUDE. INCHES. Rio Janeiro, . . . 22 54' S. 12 3" S to .067 to 10 Calcutta 22 35' N to 072 St. Petersburg, . . 59 56' N. to .005 lii the tropical regions, according to Humboldt, so reg- ular are the diurnal changes, that the barometer indi- cates true time, within a quarter of an hour. These daily fluctuations, in the atmospheric pressure, for a long time, perplexed meteorologists, but their cause has, at length, been discovered, by means of the late ob- servations, at the English observatories. They are found to arise from the stated variations in temperature, that occur during the day. 24. VARIATIONS IN ALTITUDE. As we ascend above the surface of the earth, we leave a portion of the at- mosphere below us, and are freed from its pressure. This fact is denoted by the fall of the barometer. When De Luc, a French philosopher, ascended to the height of 20,000 feet, his barometer sunk to twelve inches. In 1838, the aeronaut Green, rose from Vauxhall gardens, in London, to an elevation of nearly three miles and three quarters ; the mercury in the barometer gradually de- scending, from thirty inches to fourteen and seven-tenths. 25. As a general rule, this depression, near the sur- face of the earth amounts to one-tenth of an inch for every eighty-seven feet in altitude ; but where perfect accuracy is required, several corrections must be made. The barometer then becomes, in the hands of skillful observers, an important instrument for determining alti- tudes, and so exact are its indications, that two inde- Give examples. What is said by Humboldt of their regularity in the tropics 1 How are they caused 1 How is the pressure of the air influenced by the altitude 1 What instrument indicates the changes of pressure ? In the instances given, how low did the mercury sink ? What is the law of depression 1 For what purpose is the barometer sometimes employed 7 Give instances. THE ATMOSPHERE. pender.t estimates of the height of Mount ^Etna, made by means of this instrument, dififer only one foot ; that of Capt. Smyth being 10,874 feet, while Sir John Her schel's is 10,873 feet. Fig. 2. DENSITY OF THE ATMOSPHERE. 26. When one portion of the atmosphere is said to be more dense than another, all that is meant is simply ;his ; that a given volume, or bulk, of the first portion, as one gallon, contains more aerial particles than an equal volume of the second ; thus, if it contains twice as many particles, it is said to be twice as dense. 27. The density of the atmosphere decreases with ihe altitude. This result is caused by the diminished pressure of the air, and the decreasing force of gravity. Imagine the atmosphere to be divided into a vast num- ber of thin, concen- tric strata, which in figure 2, are repre- sented by the spaces between the lines 1-2, 2-3, 3-4, 4-5, &c. Now it is clear, that the particles in each layer are pressed together by the whole weight of the atmosphere above them, while, at the same time, they are drawn together by the force of gravity. Vari- ations in the latter power are only appreciable at great distances from the earth, and the observed changes in density, at two or more stations, may therefore be as- cribed to the difference in the weight or pressure, of the superincumbent atmosphere. The height of the barom- eter, at different elevations, thus denotes the density of the air at these points. ATMOSPHERIC STRATA. When is one portion of the atmosphere denser than another ? What two causes principally influence its density ? Describe figure 2 Which cause may be neglected 1 What instrument measures the density 1 DENSITY OP THE ATMOSPHERE. 23 28. The density, however, is not exactly proportioned to the pressure, slight modifications arising, from sev- eral causes ; the most important of which is tempera- ture. The heat of the atmosphere decreases with the altitude, and since heat expands, and cold contracts, a given volume of air, lirrth part of its bulk, at 32, for every degree Fah. ; or in other words, thus lessens and increases its density, a correction must be made for this influence. 29. It has been found by calculation, combined with observations, that, if the altitudes are represented by an increasing arithmetical series, the densities of the at- mosphere decrease in a geometrical progression. Thus, if at the height of 18,000 feet the air, as the barometer indicates, is but half as dense, as at the surface of the earth ; at 36,000 feet it will be reduced to one-fourth, and at 54,000 feet to one-eighth of its original density. 30. The rarefaction of the air at lofty elevations, les- sens the intensity of sound, impedes respiration, and causes the minute veins of the body to swell and open. Thus, at a short distance, the report of a pistol upon the summit of Mont Blanc, can scarcely be heard. Gay Lussac and Biot, ascending from Paris, in a balloon, to the height of 25,000 feet, breathed with pain and diffi- culty, and upon the high table lands of Peru, the lips of Dr. Tschudi, cracked and burst; while the blood flowed from the veins of his eyelids. In consequence of this diminution of pressure, water boils, in such situations, at a comparatively low tempe- rature ; thus, at Quito in Equador, 9,537 feet above the sea level, ebullition takes place at the temperature of 196 Fah. la what manner does temperature affect the density ? What is the law of decrease in reference to altitude ? Illustrate. What are the effects of a rarefied atmosphere 1 Give instances. 24 THE ATMOSPHERE. WEIGHT OF THE ATMOSPHERE. 31. We have seen, that a column of mercury, about thirty inches in height, weighs, at the surface of the earth, exactly the same as a column of the atmosphere, possessing the same base. If then the globe was cov- ered with an ocean of mercury, thirty inches in depth, the latter would occupy the identical base that the at- mosphere does now, and their respective weights might be regarded as equal. 32. Under this supposition, the diameter of the earth would be increased five feet. The difference then, in cubic feet, between the solidity of the earth, and that of a globe, whose diameter is five feet greater, will equal the number of cubic feet in the sea of mercury. This number multiplied by the weight of a cubic foot of mer- cury, viz. 848,125 Ibs., will equal that of the whole mass, which is the same as the weight of the atmosphere. This calculation has been made, and amounts to more than five thousand billions of tons. TEMPERATURE OF THE ATMOSPHERE. 33. The entire body of air surrounding the globe ap- pears to be warmed in two ways ; first by the luminous beams of the sun, secondly, by the radiation of heat from the earth. 34. According to Kaemtz and Martin, the atmo- sphere absorbs nearly one-half the daily amount of heat, which emanatos from the sun to the earth, even when the sky is perfectly serene. The remaining portion fall- ing upon the surface of the ground, elevates its tempera- ture, and the earth sends back into the atmosphere rays of invisible heat. 35. Modern researches have shown, that all bodies, through which heat can pass ; absorb a greater propor- How is the weight of the atmosphere computed 1 How many tons does it weigh ? How is the atmosphere warmed 1 ? THERMOMETER. 2o tion of non-luminous, than of luminous calorific rays. The heat, therefore, that radiates from the earth, will not pierce the atmosphere, with the power of the solar ray ; all will be retained by the lower strata of air, which in their turn, diffuse invisible thermic rays, in every direction. 36. We thus perceive, what all observations have proved, that the upper regions of the atmosphere must be colder than the lower. It is not, however, to be for- gotten, that the rarefaction of the superior strata con tributes to this condition. THERMOMETER. 37. The temperature of the atmosphere is indicated by the thermometer, an instrument, which derives its name from the Greek words, thermos, warm, and metron, measure. It consists of a small glass tube, terminated by a bulb, and is partially filled with mercury. This fluid is usually preferred for several reasons, the most important of which are, its uniform dilation, its quick susceptibility to any change in temperature, arid the great range of its expansion in the fluid state. If the instrument is to be exposed to extreme cold, alcohol must be used. 38. As mercury, like other fluids, expands by heat, and contracts by cold, its alternate elevations and de- pressions within the tube, can be made to indicate the corresponding changes in the state of the air, if two fixed temperatures can be found, whence to Beckon the changes. These have been discovered. If a thermom- eter is immersed, at different times, in melting snow, the column of mercury invariably sinks to the same place in the tube, though many months may have elapsed between the experiments ; and, when exposed to the steam of boiling wafer, the mercury always as- 1s it heated most by luminous or non-luminous heat? Are the upper or lower regions of the atmosphere the warmest 1 How is the temperature of the atmosphere measured ? Describe the thermometer. Why is mercury used ? Flow are the two fixed temperatures obtained 1 THE ATMOSPHERE. cends to the same height, under the same atmospheric pressure. 39. These invariable positions, which are termed the freezing and the boiling points, are marked upon the scale to which the tube is affixed. In Fahrenheit's ther- mometer, figure 3., the interval between them is divided into 180 Fig. 3. parts. each of which is called a Freezing polm Zero. degree (1) and as the freezing point is marked 32, the boiling is therefore 212. The divisions are extended downwards from 32 to 0, or the zero point, and when extreme degrees of cold are to be measured, the range is con- tinued to 20, 40, and even 60 below zero. If the air is colder than 40 below zero, a spirit ther- mometer must be used, since mer- cury becomes solid at this tem- perature. When Simpson, a late northern traveller, wintered, in 1838, at Fort Confidence, 67 N. lat., he cast a bullet of mercury, the temperature being 49 below zero. Upon firing the ball, it passed through an inch plank, at the distance of ten paces ; but flattened and broke against the wall, three or four paces beyond. In addition to the mode of graduation adopted by Fahren- heit, several others prevail (C. 570), which it is not ne- cessary here to discuss. 40. The thermometer employed for meteorological purposes, should be made as accurate as possible, and in 21S Boiling point FAHRENHEIT'S THERMOMETER Into how many intervals is the space between them divided in Fahron belt's scale ? What are the intervals called 7 How many degrees is the freezing point 1 How many the boiling point ? What is> the zero point 1 When must a spirit thermometer be used 7 Relate Simpson's experiment. SELF-REGISTERING THERMOMETER. 27 order to ensure its perfection, many niceties must be ob- served in its construction. 41. FIRST. The tube should be of equal size throughout the whole stem ; else the same increase of temperature will not produce the same increase in the height of the mercury, throughout every part of the tube ; and so of the decrease. SECONDLY. The bulb should be large in proportion to the tube ; for then slight changes in temperature will be rendered perceptible, and the delicacy of the instru- ment increased. THIRDLY. The mercury should be pure, dry, and recently boiled, in order to free it from air ; and, when in the tube, should there again be boiled, to drive off any air or moisture collected within. LASTLY. When the mercury is at the summit of the tube, and every thing" else has been expelled, the top of the tube must be perfectly closed by the fusion of the. glass, leaving, when the mercury has cooled, a void space or vacuum above. 42. When a thermometer has been exposed to great changes in temperature during the course of a year, the position of the freezing point upon the scale is found to be somewhat altered ; for, if the instrument is then placed in melting snow, the mercury is usually seen to stand a little higher than 32, and less than 33. This change would occasion a constant error in the ob- servations, and meteorologists therefore verify their thermometers at stated intervals, in tKe way just men- tioned, SELF-REGISTERING THERMOMETER. 43. The object for which this instrument is con- structed, is to obtain, in the absence of the observer, the highest and lowest temperature of the day, or of any other interval of time. What precautions must be taken to construct an accurate thermometer ? What change occurs in the position of the freezing point 1 How are thermometers verified ? For what purpose is a self- registering thermometer used 1 28 THE ATMOSPHERE. One of the most correct thermom- eters of this kind, now in use, is that invented by Mr. James Six, of Col- chester, which is represented in Fig. 4. It consists of a long glass bulb, G, narrowing into a fine tube, which is first bent downward, forming the arm a 6, and then upwards, forming the arm c d, which terminates in a small cavity, L. The two arms con- tain mercury, which extends down from a on one side, and up to c on the other : the bulb and the rest of the tube are filled with alcohol, ex- cept the upper part of the cavity L. Upon the top of the mercury in each arm rests an index (which is more perfectly seen at A), consisting of a piece of iron wire capped with ena- mel, and loosely twined with a fine glass thread ; when the mercury de- scends, the index would fall, were it not for the glass thread, which, press- ing like a spring against the sides of the tube, supports the index, in any SIX'S SELF-KEGISTERINO 44. The action of the instrument THERMOMETER. is as follows : When an increase of temperature ex- pands the spirit, the mercury is depressed in the arm a 6, and elevated in c d, carrying the index up with it. If the temperature now falls, the spirit contracts, and the mercury descends in c d\ but the index remains in its last position, from the pressure of the glass spring against the tube ; and, as it does not fit tightly to the latter, the alcohol above it flows readily by. As the cold augments, the mercury rises in a b, bear- ing up the index of this arm, until an increase of tem- perature occurs, when the mercury here falls, and the Describe Six's, from fig. 4. MEAN DAILY TEMPERATURE. 29 index continues stationary. Thus, the highest point co which the index rises in the arm, a b, indicates the least temperature, and that in c d the greatest, that happens in any interval of time, as a day, or a year ; and tho sca'e, as is evident from the figure, is graduated accord- ingly. 45. After every observation, each index requires to be adjusted ; this is done by means of a magnet, which, being moved down the side of the arm, draws the index after it. Another instrument of this kind was invented by Rutherford, (C. 575.) MEAN DAILY TEMPERATURE. 46. The mean or average temperature of the day, would be accurately found by observing the thermom- eter at intervals of an hour during the whole twenty- four, and dividing the sum of the temperatures by the number of observations, viz., twenty-four. This method is however too laborious, and meteorologists have en- deavored to arrive at the same result from two or three daily observations. 47. According to Kaemtz, a celebrated German me- teorologist, if, in Germany, the thermometer is noted at 6, A. M., 2, P. M., and 10, P. M., and the sum of the temperatures divided by three, the quotient will differ but little from the true mean. The rule adopted in the State of New York, under the direction of the Regents of the University, is as follows : Mark the temperature, first, between daylight and sunrise ; secondly, between 2 and 4, P. M. ; thirdly, an hour after sunset : add together the first observation, twice the second and third, and the first of the next day, and divide the sum by six ; the result will be the mean. The mean daily temperature at Philadelphia has been found, from the hourly observations of Capt. Mor- What is understood by the mean daily temperature ? How is it obtained? 30 THE ATMOSPHERE. decai, to be one degree less than the temperature at 9, A. M. 48. By taking the average of all the mean daily tem- peratures throughout the year, the mean annual tem- perature is ascertained. It is also obtained by the aid of the self-registering thermometer, the average of the two extreme temperatures being regarded as the mean of each day. 49. VARIATIONS OF TEMPERATURE IN LATITUDE. By comparing situations differing widely in latitude, it is found that the average annual temperature of the atmosphere diminishes from the equator towards either pole. This will be seen from the annexed table, which presents the results at the sea level, for nine places. PLACES. LAT. TEMP. PLACES. LAT. TEMP. Falkland Isles, Buenos Ayres, Rio Janeiro, . Maranham, . Trincomalee, 51 S. 34 36' S. 22 56' S. 2 29' S. 834'N. Fahren. 47 .23 62 .6 73 .96 81 .32 81 .32 Calcutta, . . Savannah, London, . Melville Isle, . 2235'N. 3205'N. 5131'N. 7447'N. Fahirn. 73 .44 64 .58 50 .72 1.66 be- low zero. 50. From this table it is also evident, that places hav- ing the same latitudes, in the two hemispheres, do not necessarily possess the same average temperature. This is owing to a great variety of local causes, the effect of which cannot always be accurately estimated. 51. VARIATIONS IN ALTITUDE. The temperature of the air diminishes with the altitude, but the law of de- crease is very irregular, being affected by the latitude, seasonn, hours of the day, and a diversity of local cir- cumstances. It may however be assumed, as a gen- eral rule, that a loss of heat occurs to the extent of one degree Fah.for every 343 feet of elevation. This is an How is the mean annual temperature found 1 How does the temperature of the atmosphere vary in respect to latitude 7 Give examples Do like latitudes in different hemispheres have the same temperature 1 How is the temperature affected by altitude 1 What i the general law of decrease 1 MEAN DAILY TEMPERATURE. 31 average result, for the rate of decrease is very rapid near the earth, after which it proceeds more slowly, but at the loftiest heights is again accelerated. 52. During the winter of 1838, the French scientific commission stationed at Bossekop, in West Finmark, 69 58 N. lat., found this law partially reversed, amid the rigors of a polar clime ; the temperature of the atmosphere increasing, nearly, 3 Fah. for the first 328 feet in height ; beyond this limit it began to decrease, at first slowly, but afterwards with greater rapidity. Dur- ing the summer, the temperature decreased with the altitude. 53. As a consequence of this gradual reduction of heat, a point at length may be attained, in any latitude, if we continue to ascend, where moisture, once frozen, always remains congealed. Hence, arise the eternal snows and glaciers, that crown the summits of the high- est mountains. 54. Since the mean temperature of the air is highest at the equator, and sinks towards either pole, the points of perpetual congelation are farthest removed above the ocean-level within the torrid zone, and gradually ap- proach nearer the general surface of the earth, with th increase of latitude ; as the following table shows. PLACES. LATITUDE. LOWER LIMIT OF PERPETUAL SNOW. Straits of Magellan. . . . Chili . . 54 S. 41 3,706 feet. 6 009 Q,uito . . . 00 15 807 Mexico . 19 N 14 763 .ZKtna 37 30' 9 531 Kamschatka 56 40' 5 248 Isle of Mageroe, Norway, 71 15' 4,362 55. A striking departure from the rule exists, how ever, in India ; for while on the south side of the Him- snaiehs, the snow line occurs at the height of about Was it found true at Bossekop 1 What results from this gradual loss of heat ? Where are the points of perpetual congelation nearest to the ocean? Where farthest from it 7 Give examples. 32 THE ATMOSPHERE. 13,000 feet, on the northern acclivity it rises to the alti- tude of 17,000. Many explanations of this singular facl Have been given, which admit not of discussion here. HUMIDITY OF THE ATMOSPHERE. 56. At all temperatures moisture resides in the atmo- sphere, self-sustained, in an invisible state. Between the particles of air intervals are believed to exist, which are, either partially, or wholly, filled with the vapor that constantly rises from the earth. 57. This peculiarity in the constitution of the atmo- sphere is termed the capacity of the air for inoisture, and when the intervals are full of vapor, it is said to be saturated. An increase of temperature, by dilating the air, separates the particles farther from each other ; the intervals are thus enlarged, and the capacity of the air Increased. A diminution of temperature is followed by contrary effects ; the size of the intervals is then redu oed, and the capacity lessened. 58. The capacity increases, however, at a faster rate : han the temperature. A volume of air, at 32 Fan. is capable of containing a quantity of moisture, equal to the i 60lh part of its own weight ; but for every twenty seven additional degrees of heat, this quantity is doubled. Thus a body of air can contain, At 32 Fah. the 160th part of its own weight. " 59 " 80th " " " 86 " 40th " " 113 " 20th " Prom this it follows, that while the temperature ad' vances in an arithmetical series, the capacity is accel- erated in a geometrical progression. What departure from this rule exists 1 What does the atmosphere contain at all temperatures 1 What is meant by the capacity of the air for moisture 1 When is 'the air said to be saturated 1 ? What is the effect of heat upon the capacity 1 What is the effect of oold 1 Which increases at the fastest rate, temperature or capacity ? Give instances. What is the rule in respect to temperature and capacity f HUMIDITY OP THE ATMOSPHERE. 33 59. ABSOLUTE HUMIDITY. From the cause just men- tioned, it would naturally be inferred, that the quantity of atmospheric vapor, or the absolute humidity ', is great- est in the equinoctial regions, and diminishes towards either pole ; a conclusion abundantly supported by facts as will be shown hereafter. 60. The air over the ocean is always saturated, and upon the coasts, in equal latitudes, contains the greatest possible amount of vapor ; but the quantity decreases aa we advance inland, for the atmosphere of the plains of Oronoco, the steppes of Siberia, and the interior of New Holland, is naturally dry. 61. The absolute humidity diminishes with the alti- tude, but the rate of reduction is not fully known. By comparing different seasons and hours, it is found to be greater in summer than in winter, and less in the morn- ing than at about mid-day. 62. RELATIVE HUMIDITY. This must not be con- lounded with absolute humidity. By relative humidity is understood the dampness of the atmosphere, or Us proximity to saturation ; a state dependent upon the mutual influence of its absolute humidity and tempera- ture ; for a given volume of air may be made to paws from a state of dampness, to one of extreme dryness, by merely elevating its temperature, without altering, in the least, the amount of moisture it contains. Thus one hundred and sixty grains of air, containing 1 one grain of vapor, would be damp at 36 Fah., but hot and withering at the temperature of 90. By the reverse of this process, a body of hot air will not only become humid, but will even part with a portion of its original moisture, if it is cooled down to any great extent. 63. From the numerous observations of Kaemtz, at Halle, and on the shores of the Baltic, it appears that What Is absolute humidity? Where is absolute hnmidity the greatest 7 How does it diminish ? Where is the air always saturated ? What is said of inland regions? What is the effect of altitude? Compare summer and winter, morning and mid-day. What is relative humidity? Upon what does it depend ? Illustrate the effects of a change of temperature, the absolute humidity being the same. 34 THE ATMOSPHERE. the relative humidity, in those situations, is highest in the morning before sunrise, and lowest, or farthest re- moved from the point of saturation, at the hour of the greatest diurnal heat. Corresponding results have been obtained in this country. HYGROMETER. 64. Those instruments by which the humidity of the atmosphere is measured are called hygrometers, from the Greek words ugros, moist, and metron, measure. Of these there exists a great variety, differing both in form and piinciple ; but those are esteemed the most accurate in thcii' indications, that are constructed upon the prin- ciple of condensation, to which allusion has already Deen made, (Art. 62,) but a more extended explanation is here required. 65. Imagine a brightly polished metallic vessel, par- tially filled with water, at the temperature of 60 Fah., to be placed in a room at the same temperature. If pieces of ice are now thrown into the vessel, the water is gradually cooled down, and as this reduction proceeds, the lustre of the exterior surface will be dimmed, at a certain moment, by a fine dew. This is caused by the deposition of moisture from the atmosphere, which, in contact with the cold surface of the vessel, is now cool- ed 4own just beyond the point of saturation. The tem- perature of the water at this instant, which is the same as that of the vessel, is termed the. dew-point. 66. By marking the difference, in degrees, between the temperature of the air and the dew-point, the rela- tive dryness of the atmosphere, or its remoteness from saturation is obtained. But observations, like these, lead also to other important results; for, by the aid of tables, giving the elastic force of aqueous vapor, at dif ferent temperatures, the absolute weight of the vapor, diffused through a given volume of air can be determin- Wha did Kaemtz observe in respect to relative humidity 7 What is a hygrometer 7 Explain the principle of condensation. "What is the dew-point 1 How is the relative humidity obtained 1 "What other results can be deduced? HUMIDITY OF THE ATMOSPHERE. 35 Fig. 5. HYGROMETER. od, and likewise the proportion it contains, to that which would be required to saturate it. 67. The hygrometer of Prof. Daniell, which is extensively used, is thus constructed. A glass tube, e i, figure 5., is bent twice at right angles, and terminated by two bulbs, b and/, of the same material. The bulb b is partly filled with ether, into which is inserted the ball of a delicate thermometer, d, enclosed in one arm of the instrument. All air is excluded from the tube, which is filled with the vapor of ether; the other bulb,/ is cov- ered with a piece of fine mus- lin, a, and upon the pillar, g 7i, a second thermometer, k Z, is fixed. 68. Observations are thus made. The instrument being placed by an open window, or out of doors, a few drops of good ether are suffered to fall upon the muslin-covered bulb, which, from the rapid evaporation of the ether, soon becomes cool, condensing the ethereal vapor with- in. In consequence of this effect, the ether in b evapo- rates, thus causing, not only in the ether, but also in the enclosing bulb, a reduction of temperature, which is measured by the interior thermometer, e d. As the evaporation at a proceeds, the temperature of b still continues to fall, and, at a certain point, the at- mospheric vapor will be seen gathering in a ring of dew upon the glass, and the difference in degrees, at this moment, between the external and internal thermome- ter, denotes the relative dry ness of the atmosphere. Thus, if on one day the exterior thermometer stood at 65, and the enclosed sunk to 50 ere the dew-ring ap- peared and on another, the former was at 73, and the latter had descended to 68 before the glass was dimmed Describe Daniell's hygrometer, fig. 5., and explain the mode of taking observations. 36 THE ATMOSPHERE. with moisture in the first instance the dryness of the atmosphere would be indicated by 15, and in the second by 5. 69. The action of this instrument is almost instan- taneous, for the enclosed thermometer begins to fall in two seconds after the ether is dropped, It is usual, where great precision is required, to read off the de- grees of the interior thermometer at the moment the dew-ring appears, and also at the moment it vanishes ; the average of the two observations being taken as the true dew-point. 70. In England the dew-point is seldom 30 Fah. below the temperature of the air ; the greatest differ- ence at Hudson, Ohio, as given by Prof. Loomis, is 36. In the tropical regions its range is the most extensive ; for, in the burning clime of India, the dew-point has sometimes sunk as low as 29, while the temperature of the atmosphere was 90 a difference of sixty-one degrees. 71. HEIGHT OF THE ATMOSPHERE. Whether the atmosphere is boundless or not, is a question which natural philosophers have been unable io determine. De Luc regards it as unlimited, and imagines the plan- etary spaces to be filled with a medium so exceedingly attenuated as not to retard the motions of the heavenly orbs. The earth arid the various celestial bodies are supposed to condense this subtil fluid around them into an atmosphere, by virtue of their respective attractions. 72. Were this true, the densities of the atmospheres thus formed would differ, on account of the variations ip the size and mass of these bodies. It therefore consti- tutes a strong objection to this hypothesis, that the den- sity of the atmosphere of Jupiter (as shown by the re- fraction of the light of his satellites, at the period of their eclipses) is not superior to that of our own ; although the force of attraction at the surface of this planet is al- How far below the temperature of the air does the dew-pjint descend io England 1 in Ohio 7 in India ? Is the height of the atmosphere known ? What is De Luc's opinion 1 What is the objection to tl- 3 hypochesis'i HEIGHT OF THE ATMOSPHERE. 37 most three times greater than that of the earth. More- over, when Venus passes near the sun, she exhibits no atmosphere, according to Wollaston, notwithstanding her size is nearly equal to that of the earth. 73. Those who maintain that the atmosohere is lim- ited, suppose, that at a certain distance from the earth, the expansive energy of its particles is exactly balanced by the force of gravity, and that beyond this point, an infinite void extends. This distance has been computed to be not far from 22,200 miles from the centre of the globe. 74. Whichever theory may be adopted, it is certain that the atmosphere extends to very great heights. Dr. Wollaston has shown, by calculation, that the atmos- phere, at the altitude of ne&rly forty miles, is still suffi- ciently dense to reflect the rays of the sun, when this luminary is below the horizon. It is capable of trans- mitting sound at a loftier elevation, for in 1783, a vast meteoric body exploded at an altitude of more than fifty miles, the sound reaching the earth like the report of a cannon. Still farther ; if the combustion of meteors is truly assigned to the action of the atmosphere, the ex- istence of the latter, at the distance of one hundred miles from the earth, may be regarded as proved. What do the advocates of a limited atmosphere suppose 7 How far is this point from the earth's centre 7 At what height does the atmosphere reflect light 1 At what alt/.tude transmit sound 1 W'nat inference is drawn from the combustion of meteor1 PART II. AERIAL PHENOMENA. CHAPTER I. OF WINDS IN GENERAL. 75. CAUSE OF WIND. Wind is air in Motion, occur- ring whenever the repose of the atmosphere is broken, from any cause whatsoever. It is usually the result of a change of temperature, and consequently of density, but the rush of an avalanche, causing a sudden displace- ment of a vast volume of air, has been known to pro- duce a momentary wind of great violence, along the borders of its path. 76. If two contiguous, upright columns of air, with their bases at the same level, are unequally heated, the colder is the denser, and at its base a current will How towards the lighter column, (just as the compressed air within a bellows streams out into the rarer atmosphere,) but at the top, to supply this loss, a counter current pre- vails. 77. This is illustrated by Franklin's simple experi- ment; if a door is opened, communicating between a warm and cold room, and a lighted taper then placed at the bottom of the doorway, the flame is bent towards the warm apartment ; but if held at the top, its direction is reversed. 78. On account of the unequal distribution of heat What does part second treat of? What does chapter first treat of 'I Define wind. When does it occur ? If two contiguous columns of air are unequally heated, what motion takes place? State Franklin's experiment. OF WINDS IN GENERAL. 39 over the surface of the globe, phenomena like these occur in nature, on a widely extended scale ; for if two neigh- boring countries are unequally heated, the air above them partakes of their respective temperatures, and there arises at the surface of the earth, a wind blowing from the colder to the warmer region, while at the same time, a directly contrary current prevails in the upper strata of the atmosphere. 79. VELOCITY. Every gradation exists in the speed of winds, from the mildest zephyr, that scarcely bends the flower, to the most violent hurricane, which pros- trates the giant oak, and hurls to the ground the proud- est works of man. They have been classed as follows, by Smeaton, according to their rapidity and force. Velocity of the wind, miles per hour. Perpendicular force on one square toot in Ibs. avoirdupois. Common appellation of such winds. 1 .005 Hardly perceptible. 4 5 .079 .123 I Gentle wind. 10 15 .492 1.107 Pleasant brisk gale. 20 25 1.963 3.075 Very brisk. 30 35 4.429 6.027 High wind. 40 7.873 Very high. 50 12.300 Storm. 60 17.715 Great Storm. 80 31.490 Hurricane. 100 49.200 Violent Hurricane. 80. The velocity of the upper currents of the atmos- phere, is as variable as that of the winds which sweep over the surface of the globe ; for the aeronaut, Green, who ascended from Liverpool, in 1839, to the height of 14,000 feet, encountered a current that bore him along at the rate of five miles per hour, but upon descending to the altitude of 12,000 feet, he met with a contrary wind, blowing with a velocity of eighty miles per hour. How does it explain the origin of winds ? What is said of the velocity of winds 1 Give the common appellations of winds, with their velocity and force. What is said of the speed of the upper currents ? Give examples. 40 AERIAL PHENOMENA. On one occasion, his balloon was carried over the space of ninety-seven miles in fifty-eight minutes. 81. ANEMOMETER. The velocity of the wind is esti- mated by the anemometer, an instrument so called from the Greek words, anemos, wind, and metron, measure. One of the best is Woltmann's. It consists of nothing more than a small windmill, to which is attached an index, in order to mark the number of revolutions per minute: the number of course increasing with the speed of the wind. Now if the atmosphere is still, and the anemometer is carried against it at the rate, for instance, of ten miles per hour, the number of its revolutions will be exactly the same as if the instrument was sta- tionary, and the vanes revolved by the force of a breeze possessing the same velocity. 82. If then, upon a calm day, the anemometer is taken upon a railroad car, moving, for example, at the speed of twenty miles an hour, and the number of revo- .utions for half an hour accurately noted, we can obtain, (by dividing this result by 30,) the number of revolu- tions per minute, corresponding to those of a wind ha\ - ing a velocity of twenty miles per hour. In this manner, a table adapted to the instrument can be constructed for all winds, moving with a greater or less rapidity. The velocity of the higher aerial currents is ascer- tained by the speed with which the shadow of a cloud passes over the surface of the earth. 83. FORCE. The force of the wind is obtained, by observing the amount of pressure it exerts upon a given, plane surface, perpendicular to its own directions. If the pressure-plate acts freely upon spiral springs, the power of the wind is denoted by the extent of their compression, and that weight will be a measure of its force, which produces the same effect upon the springs. This instrument, which is also termed an anemometer^ What is an anemometer? Describe Woltmann's, and the mode of com- puting by it the velocity of the wind. How do we judge of the speed of the upper currents? In what manner is the force of the wind estimated? TRADE WINDS. 41 is constructed in exactly the same manner as a letter weigher, where a weight of half an once compresses thDead Calm. 8 20 28.09 8 23 28.44 S. S. E. 8 33 28.53 S. E. 8 38 28.62 S. E. 8 45 28.71 S. E. 8 50 28.80 S. E. 9 28.98 S. E. 9 10 29.16 S. E. > Hurricane. 9 25 29.24 S. E. 9 35 29.33 S. E. 9 50 29.42 S. E. 10 10 29.51 S. E. 10 35 29.60 S. E. 11 30 29.64 S. E. Aug. 3d, A.M. 2 45 29.78 S. E. 8 29.91 S. W. 9 29.93 E. 130. In the case of the Water Witch, we have seen, that, when the centre of the tempest was past, arid the* gale abated, the barometer rose an inch. 131. CIRCUIT SAILING. The gyratory motion of hur- ricanes is strikingly evinced by vessels sailing on a cir- cular course, when scudding before the wind. The most remarkable case is that of the Charles Ileddle, related by Mr. Piddington, which occurred in a storm, near Mauritius, in Feb. 1845. It appears from the log-book of this ship, that, in her course before the gale the wind changed completely What example is given of circuit sailing? HURRICANES. 61 round five times in the space of one hundred and seven- teen hours, having an average velocity of eleven miles and seven-tenths per hour. The whole distance thus sailed by the vessel was thirteen hundred and seventy- three miles ; while her actual progress during this time in a south-westerly direction, was found to be only three hundred and fifty-four miles. 132. Axis OF THE HURRICANE. The axis of the hurricane is not, necessarily, upright, but is usually in- clined to the horizon ; leaning in the direction which the tempest takes. This is owing to the friction of the base of .the hurricane against the surface of the earth. Its velocity is thus checked, while the upper portion is driven forward, and overhangs the base. This position of the axis is indicated by the circum- stance that the tokens of the approaching tempest often appear in the higher regions of the atmosphere, before it is felt below. The navigators of the tropic seas some- times behold, high in the air, a small black cloud ; rapidly it spreads down to the horizon, shrouding sea and sky, and the tempest then suddenly descends upon them in all its fury. 133. REMARKS. Such are the opinions entertained by Redfield, Reid, Dove, and others, in regard to storms and hurricanes ; opinions based upon a vast assemblage of facts and observations, gathered from all points, within the track of a great number of these desolating gales. The numerous observations taken upon the American coast, commensurate with the extent of the Atlantic tempests, have been systematized by Mr. W. C. Redfield, of New York ; while Col. Reid has investi- gated the West India hurricanes, and those of the southern hemisphere, with great success. The log- books of the British navy, in which the phenomena of the weather are recorded every half hour, have been What is the position of the axis of the hurricane ? How Is it caused ? How is this position sometimes 'ndicated 1 * Detail the labors of Redileld, Reid, and Dova 62 AERIAL PHENOMENA. placed at nis disposal, and he has thus been furnished with an immense collection of valuable facts. Prof. Dove, of Berlin, has studied the laws of hurricanes in Europe, and gathered a large number of observations from every quarter of the globe. By noticing the time and place of each observation, storm-charts have been constructed for the use of mariners, and it is highly in favor of the rotary theory, that the conclusions result ing from these extensive and independent investigations are substantially the same. 134. ESPY'S THEORY. The rotary character of hur- ricanes, including tornadoes and water-spouts, is how- ever denied by Mr. Espy, of Philadelphia, who main- tains that the wind blows from every quarter towards the centre of the storm. Espy asserts, that this law ob- tains without a single exception, in seventeen storms which he has investigated. The influx of wind towards the centre, he supposes to be caused by the development of heat, which occurs whenever atmospheric vapor is condensed in the form of a cloud. The heat, thus dia engaged, rarefies the surrounding air, and establishes an upward current ; and so great an expansion is be- lieved, at times, to result from tins cause, that the ve- locity of the ascending current has been computed to exceed three hundred and fifty feet per second. To this point of greatest rarefaction, the atmosphere rushes in from every side, just as the air of a room flows towards the heated current of the chimney ; the violence of the wind depending upon the rate of speed in the ascending column. Most of the phenomena of meteorology are also explained by Mr. Espy in accord- ance with his peculiar views. 135. The centripetal theory has found many able supporters ; but that of Redfield and Reid has been more generally adopted by men of science. 136. It may perhaps be found, when our investiga- tions are multiplied and more extended, that both these Detail Mr. Espy's theory. Which theory has been more generally adopted 1 May these two motions co-exist 7 TORNADOES OR WHIRLWINDS. 63 motions often co-exist ; a circumstance which is by no mean's impossible. For when a whirlwind is once in motion, from any cause whatsoever, the great rarefac- tion of air that occurs at the centre, will create an influx of the atmosphere towards this point from all quarters, except where it is opposed by the centrifugal force. Now if the base of the whirl is above the sur- face of the earth, or when touching it, is inclined to it, (which is usually the case,) currents of air will flow beneath the base towards the vortex, and evidences of centripetal action will not he wanting. CHAPTER III. OF TORNADOES OR WHIRLWINDS. 137. Tornadoes may be regarded as hurricanes, dif- fering chiefly in respect to their extent and continuance. They last only from fifteen to sixty or seventy seconds, their breadth varies from a few rods to several hundred yards, and it is probable that the length of their track rarely exceeds twenty-five miles. 138. FACTS. This phenomenon is usually preceded by a calm and sultry state of the atmosphere ; when sud- denly the whirlwind appears, traversing the earth with great velocity, and sweeping down by its tremendous power the mightiest products of nature, and the strongest works of man. Ponderous bodies are whirled aloft into the air ; trees of large dimensions twisted off or torn up by the roots ; buildings of the firmest construction pros- trated, and streams whirled from their beds and their channels laid bare. A whirlwind that occurred in Silesia, in the year 1820, carried a mass weighing more than 650 Ibs., fifty feet above the top of a house, and What are tornadoes ? Describe their effects. By what phenomena are they attended 7 64 AERIAL PHENOMENA. deposited it on the other side in a ditch, one hundred and fifty paces distant. 139. In 1755 a tornado fell upon the village of Mira- oeau, in Burgundy, laying dry the channel of the small river by which it is traversed, and carrying the stream to the distance of sixty paces. In the New Haven whirlwind of 1839, and in that which occurred at Chate- nay, near Paris, during the same year, trees eighteen inches in diameter were torn up by the roots. In one which happened at Maysville, Ohio, in 1842, a barn containing three tons of hay and four horses, was lifted entirely from its foundations. And such was the force of the wind during a tornado which occurred at Cal- cutta in 1833, that a bamboo was driven quite through a wall five feet thick, covered with masonry on both sides ; an effect which was estimated, by a person on the spot, to be equal to that produced by a cannon car- rying a six-pound ball. By the action of a tornado, fowls are often entirely stripped of their feathers, and light substances carried to a distance varying from two to twenty miles. 140. The whirlwind is attended by all the usual phenomena of thunder-storms ; showers of hail fre- quently occur, and, at times,, it is the scene of very extraordinary electric appearances. In the one which happened at Morgan, Ohio, on the night of the 19th of June. 1823, a bright cloud of the color of a glowing oven, and apparently half an acre in extent, was seen moving below the dark canopy of the tempest. It shone with a splendor above that of the full moon, and ten minutes after its passage, the narrator of the phenomena was enabled to read his Bible by its light. Just before the Shelbyville tornado, which took place at midnight, on the 31st of May, 1830, two luminous clouds were seen approaching each other, of the color of red hot iron; for a moment they united above the town, ex- tending over it like two fiery wings, and, at the next, rushed down to the earth : at this instant the whirlwind burst in all its fury upon the devoted spot. The writer What extraordinary appearances are sometimes seen? TORNADOES OR WHIRLWINDS. 65 of this work was informed by an eye-witness, that, dur- ing the prevalence of the storm, so incessant was the play of the lightning, that the titles of books could be easily read, and the use of lamps was discarded in going to different parts of the house. 141. ORIGIN. Several theories have been advanced to explain the causes of whirlwinds, but they are sup- posed to be generally produced by the lateral action of opposing winds, or the influence 'of a brisk gale upon a portion of the atmosphere in repose ; in a manner anal- ogous to the eddies that arise at the junction of two streams, flowing with unequal velocities, or the air- whirls that occur, when a wind sweeps by the corner of a building, and strikes the calm air beyond it. 142. The existence of such opposing currents is fully proved by the observations of aeronauts, as well as by those of observers at the surface of the globe. The whirl appears to originate in the higher regions of the atmosphere, and as it increases in violence, to descend ; its base gradually approaching until it touches the earth. Thus, when on the summit of the Rigi a mountain in Switzerland Kaemtz beheld two masses of fog ap- proaching each other, in the valley of Golclan, while the air around him was cairn, and the sky serene. As soon as they united, a gyratory motion was perceived, the fog rapidly extended, accompanied with violent gusts of rain and hail. At the same time, (as appeared from subsequent information,) a furious storm fell upon the lake of the Four Cantons, far below ; in the midst of which a water-spout was seen. (Art. 150.) 143. WHIRLWINDS EXCITED BY FIRES. Extensive conflagrations have been known also to produce whirl- winds, in consequence of the strong upward current, resulting from the great expansion of the heated air. A remarkable instance of this kind occurre 1 between How do they originate, and where? What did Kaemtz witness ? What is the effect of extensive fires 7 GO AERIAL PHENOMENA. Great Harrington a. id Stockbridge, Mass., in the month of April, 1783, and is thus related by Mr. T. Dwight, who beheld it. " In an open field, a large quantity of nrush-wood was lying in rows and heaps for burning, perfectly dry and combustible. On a certain day, when the atmosphere was entirely calm, the brush was ignit- ed on all sides of the field at once. I was residing at this time, at the distance of about half a mile from the fire, when suddenly my attention was aroused by a loud, roaring noise, like heavy thunder. Upon going to the door, I beheld the fire covering the field, and the flames collected from every side into a fiery column, broad at the base, tapering upward, and extending to the height of 150 or 200 feet. This pillar of flame revolved with an amazing velocity, while from its top proceeded a spire of black smoke, to a height beyond the reach of the eye, and whirling with the same velocity as the fiery column. During the whole period of its continuance, the column of flame moved slowly and majestically around the field. The noise of the whirlwind was louder than thunder, and its force so great, that trees six or eight inches in diameter, which had been cut, and were lying on the ground, were whirled aloft to the height of forty or fifty feet." 144. During the terrible conflagration of Moscow, in 1812, the air became so rarefied by the intense heat, that the wind rose to a frightful hurricane ; the roar of the tempest being heard even above the rushing sound of the conflagration. 145. RESULTS OP CENTRIFUGAL ACTION. By the centrifugal action of the whirl, the air is driven outward^ as in the case of hurricanes, and at the same time spi- rally upwards, on account of the pressure of the sur- rounding atmosphere: a great rarefaction, therefore, occurs at the centre. As long as the base of the whirl- wind is above the ground, the warm air of the earth will stream 'under and upwards, into this partial void Give the cases. fctate the result of centrifugal action. TORNADOES OR WHIRLWINDS. 07 from every quarter ; while, at the same time, the cold air will descend into it from the higher region of the atmosphere. By this union, a powerful condensation of vapor oc- curs ; causing the precipitation of rain and hail, and the development of electricity. 146. These, however, constitute no 'essential part of a whirlwind ; for, if the currents of air that give rise to this phenomenon are very dry, the violence of the wind is the only remarkable circumstance. This was shown in the case of a small whirl, which involved two persons, who were going one cloudy day from Halle to Gie bichenstein. Suddenly they were separated by a gust of wind ; one being driven against a wall, and the other thrown into a field ; while the people who were near had not discerned the slightest disturbance in the at- mosphere. 147. When the base of the whirlwind descends to the earth, it touches the surface, either partially or wholly, according as the axis is inclined or vertical. In the first case, the inward flowing currents will be partially, and in the second entirely, arrested by the centrifugal action of the storm. The same results often occur when it covers a build- ing. Hence, the atmosphere becomes exceedingly rare- fied, both above, and around the edifice ; and if it hap pens to be closed, and the tornado is violent, its walls will be burst outward by the sudden expansion of the air within, (C. 509.) Just as a sealed bottle of thin glass, under the exhausted receiver of an air-pump, is shivered by the elastic force of the enclosed air. 148. EFFECTS OF EXPANSION. In the tornado that happened at Natchez, in 1840, the houses exploded wherever the doors and windows were shut; the roofs shooting up into the air, and the walls, even of the strongest brick buildings, bursting outward with great Are rain, hail, and electricity necessary to the production of a whirl wind 'I Give the case. Why are buildings burst outward by the action of tornadoes *? Give instances. 08 AERIAL PHENOMENA. force; but no such destruction occurred when a free outlet was afforded to the air within. One gentleman as the storm approached, caused all the windows and doors of his house to be opened, and though its struc- ture was frail it experienced no injury ; not even a single pane of glass being broken. 149. On the 18th of June. 1839, a whirlwind (to which we have alluded) fell upon the village of Chate- nay, near Paris. In the room of a house, over which it passed, several articles of needlework were lying upon a table : the next day some of them were found in a field, at a great distance from the house, together with a pillow-case taken from another room. They must have been carried up the chimney by the rush of air out- wards, as every other means of exit was closed. An- other singular illustration of the fact before us took place in the Shelbyville tornado. Soon after its occur- rence, a lady missed a bonnet, which, the day before the storm, was lying enclosed in a bandbox in her cham- ber ; some weeks afterwards, she accidentally observed a ribbon hanging from the chimney, which proved to be the string of her bonnet. The house had been closed during the storm, and the expansion of the air within the bandbox had forced off the lid the lost article had been borne by the outward flowing current up the chim- ney, which afforded the only mode of egress, and there it had lodged. CHAPTER IV. WATER-SP OUTS. J5U. A WATER-SPOUT is a whirlwind over an ex^ pause of water, as the sea or a lake, differing from a land-whirl in no other respect than that water is sub- jected to its action, instead of the bodies upon the sur- face of the earth. 151. A water-spout usually presents the following Define a wator-spout. WATER-SPOUTS. )M successive appearances. At first it is seen as an invert- ed cone, either straight or slightly curved, extending downward from a dark cloud to which it seems to be attached. As the cone approaches the surface of the water, the latter becomes violently agitated, and, rising in spray or mist, is whirled round with a rapid motion. As the cone descends lower the spray rises higher and higher, until both unite, and a continuous column ia formed extending from the water to the clouds. . The spout is now complete, and appears as an im- mense tube, possessing both a rotary and progressive motion ; bending and swaying under the action of the wind as it advances on its course. When the observer is near, a loud, hissing noise is heard, and the interior of the spout seems to be traversed by a rushing stream. After continuing a short time the column is disunited, and the dark cloud gradually drawn up ; for a while a thin, transparent tube remains below, but this at last is also broken, and the whole phenomenon then disap pears. These successive changes are represented in figures 9, 10, 11, which are taken from sketches of water- spouts actually seen. Fig. 9. WATER-SPOUT FORMING. What are its successive appearances ? AERIAL PHENOMENA. Fig. 10. WATER-SPOUT FORMED. Fig. 11. WAT.5R-SPOUT ENDING. 152. FACTS. A water-spout occurred at Cleveland Ohio, in September, 1835, which, from the description Describe the one which was seen at Cleveland. WATER-SPOUTS. 71 well illustrates the origin and characteristics of this phe- nomenon. " A heavy storm-cloud, driven b}^ a north- west gale, was met by a strong opposing current; when an arm of the cloud appeared to drop down, and drag the waves up towards the sky. The whirling and dashing of the spray at the surface of the lake, and the column of water and mist extending, in a tall and tor- tuous line, to the cloud, were so well defined as to ex- cite the admiration of all who observed them. At the expiration of about seven minutes, the north-wester tri- umphed, and swept the cloud to the south-east of the city." 153. The water-spout does not always pass through the various changes that have been detailed ; sometimes the upper portion only is developed, depending from a mafcs of black clouds, like a huge, tapering trunk, with- out ever reaching the water; at other times, nothing is seen but the cloud of spray and mist that forms the base. On the voyage of the Exploring squadron from New Zealand to Tongataboo, a spout was beheld in the act of foiming, at the distance of about half a mile. A cir- culai motion was distinctly perceived, the water flying off in jets from the circumference of a circle, apparently fifty ieet in diameter. A heavy, dark cloud hung over the spot, but no descending tube appeared, nor was there any progressive motion. In a short time the cloud dis- persed, and the surface of the sea resumed its former state. 154 It is by no means uncommon for several water- spouts to appear at the same time. In May, 1820. Lieutenant Ogden beheld, on the edge of the Gulf stream, no less than seven in the course of half an hour : vary- ing in their distance from the ship from two hundred yards to two miles. 155. DIMENSIONS. The diameter of the spout at its base ranges from a few feet to several hundred, and its Does the water-spout always undergo these changes 1 Under what forms is it sometimes seen 1 How many have been seen at once ? What is the breadth and height of water-spouts ? 72 AERIAL PHENOMENA. altitude is supposed by some to be at times as great aa a mile. In the account given by the Hon. Capt. Napier, of a spout which he beheld in 30 47' N. Lat., and 62 40' W. Lon., the diameter was judged to be 300 feet ; and the height of the column to the point where it en- tered the hanging cloud, was computed, from observa- tions taken by the quadrant, to be 1720 feet, or nearly one-third of a mile. 156. POPULAR ERROR. It is a common belief, that water is drawn up by the action of the spout into the clouds but there is no proof, whatever, of a continuous column within the whirling pillar, and the fact, that the water, which sometimes falls from a spout upon the deck of a vessel at sea is always fresh, sufficiently re- futes the idea. The torrents of rain, by which this phe- nomenon is often accompanied, can be fully accounted for by the rapid condensation of vapor that occurs, when the warm, humid air of the sea flows inward to the vortex of the whirl, and there combines with the cold air of the upper regions of the atmosphere, which de- scends to fill the partial void. From this union the electric phenomena of water-spouts arise, and the vio- lent hail-showers that at times prevail ; the mode, how- ever, in which they originate, will be explained here- after. When a vessel is in the vicinity of water-spouts, can- non shots are usually fired for the purpose of destroying them ; lest the vessel should be injured if a spout were to pass over it. It is not improbable that such an effect may be produced when the spout is either struck by the balls, or violently agitated by the concussion of the air arising from the discharges. 157. SAND PILLARS. Another form of the whirlwind is exhibited in the pillars of sand, which are not un fre- quently seen in the deserts of Africa and Peru. Bruce, on his journey to Abyssinia, beheld eleven vast columns of sand of lofty height, moving over the plain at the What popular error exists in regard to this phenomenon 1 For what purpose are cannon discharged 1 Where do sand pillars occur? WATER-SPOUTS. 73 same timt ; some with a slow and majestic motion, and others with great velocity. Now, with their summitR reaching to the clouds, they rapidly approached the terrified observers, and, the next moment, were borne away by the wind with incredible swiftness. Their tops, at times, were seen separated from the main pillars, and the latter were often broken in two, as if struck by a cannon shot : the diameter of the largest was about ten feet. While Mr. Adanson was crossing the river Gambia, a sand-whirl, twelve feet in breadth and two hundred and fifty in height, passed within forty yards of his boat. 158. The same phenomena are seen upon the Peru- vian coast. "The sand," says Dr. Tschudi, "rises in columns from eighty to one hundred feet high, which whirl about in all directions, as if moved by magic. Sometimes they suddenly overshadow the traveler, who only escapes by rapid riding." 159. BENEFICIAL EFFECT OF WINDS. The utility of winds must be evident to all. By their aid vast oceans are crossed, and the products of distant climes wafted from shore to shore. Different nations are linked to- gether by social and commercial ties, the blessings of civilization diffused, and the glad tidings from a better world borne to every land. The growth and decay, both of animal and vegetable life, vitiates the atmosphere, and renders it unfit for respiration ; but the winds prevent the deadly effects that would flow from this source, and the air becomes pure and salubrious, from its constant circulation. Even the fierce tempest may be a messenger of mercy, by sweeping from the air the seeds of pestilence and contagion. The advantage of winds in distributing moisture to e seen ? What the size that the red ray may be visible 1 How is the secondary bow formed 1 RAINBOW. 426. The subject is Fig. 23. further illustrated by the following figure, where the four parallel lines represent rays of the sun falling upon four drops of water, and O P the direction of an- other ray imagined to pass through the eye of the spectator, R O and V O are the red and vio- let rays of the primary bow; R' O and V O the red and violet rays of the secondary ; and the positions of the red and violet arches of the RAINBOW. two bows are indicated by the dotted lines. The other colored arches are found between the red and violet, following the order of colors in the prismatic spectrum. P is the centre of the rainbow. 427. In the explanation just given, we have reasoned as if the rain-drops were stationary, which of course is not the case ; but this supposition leads to no error, inasmuch as the air is filled with rain-drops during the prevalence of a shower, and before one set of drops, by sinking too low, ceases to present to the eye the colors of the bow, another set has descended, taken their place, and is performing their office. While the observer is stationary the rainbow is fixed in position, but the drops that give rise to its glowing tints are continually changing. 428. BREADTH OF THE Bows. The angular distance from the middle of the red arch to the middle of the violet in the inner bow, is the difference between 42 Illustrate farther from figure 23. Why is tho bow stationary although the drops are in motion ? 174 OPTICAL PHENOMENA 2' and 40 17' or 145'; a quantity nearly equal to three and a half times the apparent breadth of the. sun. This space is occupied by the remaining five colored arches, and, as each is 32' in width, (Art. 421.) they ne- cessarily overlap one another, and cause, by their mutual blending, an indistinctness in the boundary of the several hues. The two half-breadths of the red and violet arches added to 1 45' give the whole width of the bow, which is equal to 2 17', or about four and a half times the apparent diameter of the sun. 429. The breadth of the exterior bow, from the mid- dle of the red to that of the violet, is found in like man- ner to be 3 10' the difference between 54 9' and 50 59'. To this quantity 32' must be added to obtain the entire breadth. The interval between the bows, computing from the, red of the primary to that of the secondary, is 8 57'. All these results, deduced theoretically, precisely agree with those obtained by actual measurement. 430. POSITION AND SIZE OF THE RAINBOW. Since the centre of the rainbow is in the direction of the line imagined to be drawn from the sun through the eye of the spectator, its position will evidently vary with that of the spectator, and its size with the altitude of the sun. If this luminary is 42 2' above the horizon, the top of the inner bow will be just visible ; but if upon the hori- zon, the bow will be a semicircle, having an elevation of 42 2'. If the observer, in the latter case, were upon the summit of a mountain, the arch would be somewhat greater than a semicircle ; since the line of direction from the sun through his eye, would strike the sky opposite, at a point above the horizon. Should a person happen to be upon a mountain, when the sun is high in the heavens, and a shower at the same time occur in the vale below, he will some- times perceive a rainbow forming a complete circle. State what is said in regard to the breadth of the bows. What in respect to the position and size of the rainbow. When are entire circles beheld ? EXTRAORDINARY BOWS. 175 Such are said by Ulloa to be frequently seen on the mountains of Peru above Quito. The foaming waters of cataracts are often spanned by richly tinted bows, caused by the rising spray. They are regularly seen at the falls of SchafThausen, on the Rhine, and at the cataract of Niagara. At Terni, in Italy, where the river Velino rushes over a precipice 200 feet high, a bow of rare beauty is beheld. It appears, to a spectator below, arching the falls with its glowing tints, while two other bows are reflected on the right and left. 431. RAINBOWS IN THE NORTH. Rainbows are sometimes seen at mid-day. On the 13th of Dec. 1847, at one o'clock, P. M., Prof. Olm stead beheld at Yale College an entire bow in the north. During the same week, the writer observed at Hartford a similar bow at nearly the same hour of the day. Such a phenom- enon can never arise, in the case of the primary bow, unless the sun's altitude at the time is considerably less than 42, which only happens in the winter. 432. EXTRAORDI- NARY Bows. When the light of the sun is reflected from the sur- face of tranquil wa- ter, rainbows of sin- gular form are at times observed. On the 6th of August, 1698, Dr. Halley be- EXTRAORDINARY BOW. held, while walking on the walls of Chester, by the river Dee, a rainbow of the form represented in figure 24., where A B C is the primary bow, D E F the secondary, and A H G C the extraordinary bow, cutting the secondary at H and G. Its colors were arranged like those of the primary. Give the instances of rainbows over cataracts. When can rainbows appear in the north/? Explain from figure 24. the extraordinary bow seen by Halley. 176 OPTICAL PHENOMENA. 433. The sun was shining c.early upon the calm sur- face of the river, and Dr. Halley discovered that the extraordinary bow was nothing more than the rest of the circle of which the primary was a part, bent upwards by reflection from the water. A similar rainbow, formed by reflection from the river Eure, was beheld at Chartres, in 1665 ; when a faint arch was seen crossing the primary at its summit. 434. SUPERNUMERARY Bows. Arches of prismatic colors are sometimes seen, both within the primary, and without the secondary bows, to which the name of supernumerary or supplementary bows is given. 435. On the 5th of July, 1828, Dr. Brewster saw three 'supernumerary bows within the primary, each composed of green and red arches. Outside of the secondary a red arch was clearly seen, and beyond this a faint green one. At Montreal, in September, 1823, three supplementary bows were noticed by Prof. Twining, within the prima- ry ; exhibiting however, only a single color, which was violet or rather a dull red. At Hartford, Ct., on the 5th of August, 1847, at sun- set, two supernumerary bows were seen by the writer, within the primary, extending throughout the whole semicircle. The first, in contact with the primary, con- sisted of green and red arches, and the second of a sin- gle band of pale red light. The most remarkable phenomenon of this kind, was that observed by the Rev. Mr. Fisher, in Dumfrieshire, and related by Dr. Brewster, at a meeting of the Brit- ish Association, in 1840. In this case the primary was attended by Jive supernumerary bows, and the secondary by three. Kaemtz remarks, that it is not easy to account for these supplementary bows in a satisfactory manner; hut according to Young, Arago, and others they arise A^om the action of the rays of light upon each other : the explanation however, is too abstruse to be here introduced. 436. LUNAR Bows. Rainbows are sometimes pro- Relate the cases given of supernumerary bows. MIRAGE. 177 duced by the light of the moon ; their occurrence, how- ever, is extremely rare, and their tints so very faint as to be scarcely perceptible. One of the most brilliant ever beheld, was seen by Mr. Tunstalt, at Gretna Bridge, in Yorkshire, on the night of the 18th of Octo- ber, 1782. It became visible about nine o'clock, and continued, with varying degrees of brightness, till past two. At first it appeared as a distinct bow without colors, but afterwards the tints were very conspicuous and vivid, preserving the same order as in the solar bow, though paler ; the red, violet, and green being the brightest. At twelve o'clock it attained its greatest splendor. This phenomenon occurred three days before the moon was full ; during its continuance, the wind was very high, and a drizzling rain fell for most of the time. Another bow was seen by the same observer, on the 27th of February, in the same year. The colors were tolerably distinct, but the orange appeared to predom- inate. A lunar bow with colors, was also noticed near Chesterfield, about Christmas, in the year 1710, and is described by Thoresby in the Philosophical Transac- tions. CHAPTER III. OP MIRAGE. 437. When a ray of light, proceeding from any ob- ject, passes obliquely out of one medium into another of a different density, it is refracted, or bent from its course, (C. 704,) and when it reaches the eye, the object is seen in the direction of the last refracted ray. Relate the several instances of lunar bows. What is the subject of chapter third 1 In what direction is an object seen, when the rays that come from it the eye first pass through media of different densities ? 178 OPTICAL PHENOMENA. 438. Thus, if E represents the earth, and 1-2, 2-3, 3-4, dif- ferent strata of the atmosphere, decreas- ing in density from 1 to 4, a ray of light proceeding from the star S, and meeting the exterior stratum of the atmosphere at 4, will be successively refracted in the directions 4-3, 3-2, and 2-1 ; so that a spectator at 1 will not see the star S in its real position, but in the direction of 1-2 S'. For this reason all celes- tial objects, (unless in the zenith, where there is no re- fraction,) appear above their true position. (C. 703.) Thus, the sun and moon, for instance, at their apparent rising and setting are actually below the horizon. 439. The variations in the density of the atmosphere near the earth, produced by local changes in tempera- ture, occasion a similar displacement of terrestrial ob- jects ; this is ordinarily seen in the slight elevation of coasts and ships, when viewed across the sea, and is then called looming ; but to the more extraordinary phenomenon of this nature, the name of mirage has been given. When this phenomenon occurs, images of ships erect and inverted are seen in the air, delightful visions of tranquil lakes and verdant fields delude the fainting traveler of the desert, and sometimes, as in the case of Reggio, a noble city with all its splendid panorama of towers and arches, stately palaces and terraced heights, appears like a fairy scene upon the slumbering waters of the sea. Explain the effect of atmospheric refraction from figure 25. What is looming ? What is mirage? MIRAGE. 179 440. INSTANCES. On the first of Fig. :. August, 1798, Dr. Vince observed, at Ramsgate, a vessel in the dis- tance, the topmast only being visi- ble above the horizon, as at A, fig. 26. Two complete images of the vessel were seen at the same time in the air, the one at C erect, and the other below at B inverted: between them a distinct image of the sea appeared at D E. The two images were still visible when the real ship had passed entirely out of sight. 441. Similar phenomena were noticed by Capt. Scoresby in 1820, while navigating the arctic seas. In one instance he beheld from the mast-head eighteen sail of ships, at the distance of twelve miles ; one appeared taller than its. actual height, another shorter ; and above several of the rest, inverted images were seen. In 1822, he recognized his father's ship, the Fame, by an inverted image of the vessel in the air. though it was subsequently found to have been at that time thirty miles distant, and seventeen miles beyond the horizon. 442. During the late Exploring Expedition, a singu- lar instance of mirage was seen off Terra del Fuego, from the decks of the Vincennes and Peacock, and which is thus related. " On the 17th of February, 1839, we had an extraordinary degree of mirage or refraction of the Peacock, exhibiting three images, two of which were upright and one inverted. They were all extremely well defined. The temperature on deck was 54 Fah., that at the mast-head 62 Fah. A vessel, that was not in sight from the Vincennes' deck, became visible, and the land was much distorted, both vertically and horizontally. MIRAOS. Relate the several cases of mirage, IT 440445. 180 OPTICAL PHENOMENA. On board the Peacock, similar appearances were observ- ed of the Vincennes and Porpoise. There was, however, a greater difference between the mast-head temperature and that on deck, the thermometer standing at 62 Fall, at the mast-head, while on the deck it was but 50 Fah., being a difference of 12 ; that on board the Vincennes differed only 8." 443. Simpson, while exploring the coasts of the north polar seas, in the summer of 1837, beheld a remarkable display of the mirage. As he rowed over the tranquil ocean, he seemed to be traversing a valley ; the waters apparently rising on either hand, like the sides of a mountain, and the huge icebergs upon then surface ap- pearing ready to topple down upon him. 444. During the march of the French army over the sandy plains of Egypt, many instances of the mirage occurred. The villages, situated upon small eminences, were successively seen like so many islands in the midst of an extensive lake, and beneath each village appeared its inverted image. In the same direction, an image of the blue sky was seen, clothing the sand with its own bright hues, and causing the wilderness to ap- pear like a rich and luxuriant country. So complete was the deception, that the troops hastened forward to refresh themselves amid these cool retreats ; but, as they advanced, the illusion vanished, only to re-appear at the villages beyond. 445. This phenomenon is so common on the deserts of Asia and Africa, that the Koran calls every thing de- ceitful by the word serai), which signifies mirage. It re- marks, for example, that " the actions of the incredulous are like the serab of the plain ; he who is thirsty takes it for water, and finds it to be nothing." 446. While Baron Humboldt was at Cumana, he fre- quently saw the islands of Picuita and Boracha, appa- rently hanging in the air, and sometimes with inverted ^mages ; and at Mesa de Pavona, cows were beheld Where does this phenomenon frequently occur ? What instances are given by Humboldt and Tschudi 1 FATA MORGANA. 181 seemingly suspended in the air, at the distance of 2,132 yards. When Dr. Tschudi and his party were traversing a deep sandy plain, near the river Pasamayo in Peru, they beheld the figures of themselves, riding over their own heads, magnified to gig-antic proportions. 447. FATA MORGANA. This name is given to an extraordinary optical phenomenon, which has been often seen in the straits of Messina, between the island of Sicily and the Italian coast. It has been described by many writers, and, though known for centuries, has but lately been considered as the effect of mirage. The following is the description by Antonio Minasi, which is regarded as the most correct. " When the rising sun shines from a point, whence its incident ray forms an angle of about 45 on the sea of Reggio, and the bright surface of the water in the bay is not disturbed either by the wind or the current, a spec- tator placed on an eminence in the city of Reggio, with his back to the sun, and his face to the sea, suddenly beholds in the water numberless series of pilasters, arches, castles well delineated, regular columns, lofty towers, superb palaces, with balconies and windows, ex- tended valleys of trees, delightful plains with herds and Socks, armies of men on foot and horseback, all passing rapidly in succession along the surface of the sea." In a peculiar state of the atmosphere, when its dense vapors extend like a curtain over the waters, the same objects are not only reflected from the surface of the sea, but are likewise seen in the air, though not so distinct or well defined, and if the atmosphere is slightly hazy, the images seen upon the surface of the water are vivid- ly colored or fringed with all the prismatic hues. 448. But a most extraordinary instance of the mirage occurred at Hastings, on the coast of Sussex, on the 26th of July, 1798. The cliffs of the French coast are fifty miles distant from this town, and in the usual state of the atmosphere, are below the horizon and completely Describe the Fata Morgana. 182 OPTICAL PHENOMENA. hid from view ; but on the day mentioned, at five o'clock P. M., they were seen extending to the right and left for several leagues, and apparently only a few miles off. As the narrator, Mr. Latham, walked along the shore, the sailors, who accompanied him, pointed out and named the different places on the opposite coast, which they were accustomed to visit. By the aid of a telescope, email vessels were plainly seen at anchor in the French harbors, and the buildings on the heights beyond were distinctly visible. The Cape of Dungeness, which at the distance of 16 miles from Hastings, extends nearly two miles into the sea, appeared quite close to the town, and the fishing boats, that were sailing at the time between the two places, were magnified to a high degree. This curious phenomenon continued in its greatest beauty for more than three hours. The day was extremely hot, without a breath of wind. 449. A remarkable mirage of Dover Castle, was seen by Dr. Vince and another gentleman, on the 6th day of August, 1806, at Ramsgate. Fig. 27. MIRAGE DOVER CASTLE. The summits, v x w y, of the four turrets of the castle, fig. 27.,) are usually seen beyond the hill A B, which ies between the castle and Ramsgate ; but, on this day not only the turrets were visible, but the whole castle, m n r s, appeared as if it were on the side of the hill next to Ramsgate. Relate the account of the milage at Hastings, and of that at Ramsgate ERECT AND INVERTED IMAGES. 183 Between the observers and the shore, from which the hill rises, there was about six miles of sea, and from thence to the top of the hill the distance was about the same. Their own height above the water was nearly seventy feet. 450. ORIGIN. The cause of mirage has been par- tially stated ; but the subject demands a more complete explanation. The phenomena may be divided into three classes, viz. : those produced by refraction, those pro- duced by refraction and reflection conjointly, and those produced by reflection only. 451. The image of Dover Castle was probably pro- duced by refraction, simply ; for the atmosphere gradual- ly increasing in density from the lofty heights of the castle to the level of the sea, the rays of light proceeding from the edifice, reached the eyes of the spectators in a curved line, like those which emanate from a star, (Art. 438,) and the whole structure therefore appeared to the observers above its true position. 452. Phenomena, like those observed by Scoresby, are attributed to the combined influence of refraction and reflection. At such times, the stratum of air in contact with the sea is colder than that immediately above (Ait. 442), and this likewise colder than the next superior stratum, and so on. Consequently, to a certain extent, the density tf the atmosphere decreases with the distance from the ocean, and, under these circumstances, the rays of light from a ship may be so changed in direction, as they proceed through the air, that the ob- server will behold both erect and inverted images above the real object. 453. ERECT AND INVERTED IMAGES ABOVE THE OBJECT. The annexed figure will aid us in perceiving how erect images are caused. What is said respecting the cause of mirage ? Into what classes may the phenomena be divided ? Explain the mirage of Dover Castle. To what is attributed the phenomena of erect and inverted images abovo Ianation 7 Explain it fully. ORIGIN. 215 body revolving about the earth m ast not be less than 300 miles per minute, nor greater than 420. Were it less than 300 miles, the mass would fall to the earth by the action of gravity ; and if the rate exceeded 420 miles, it would pass away from the globe and never return. Within these limits, allowance being made for the motion of the earth in its orbit, and the resistance of the air, the body would revolve around the earth like the moon, approaching very near to its surface at stated periods. 527. In support of this hypothesis it is urged, that the velocity of meteorites, in general, is somewhat more than 300 miles per minute, though doubtless cases have oc- curred in which their speed was far greater. The combustion of the meteorite, through the agency of a condensed atmosphere, is by no means improbable ; for though the medium in which it moves is exceedingly rarefied, yet the velocity of the body is amazing ; and it can easily be shown by calculation, that from the condensation thus effected, an intensity of heat would be developed of which we have no conception. (Art. 551.) Moreover, as silica, magnesia, and potassa are found in meteorites, it has been conjectured, that they may originally exist there in the state of pure metals / and, that when the meteorite enters our atmosphere, combustion arises from the extraordinary affinity of these substances for oxygen. In those instances where meteorites move at a greater rate than 420 miles per minute, they are sup- posed either to revolve about the sun, and that the earth occasionally meets them in her annual progress ; or to wander through space, until they come within the supe- rior attraction of some other orb, and are then com- pelled to revolve around it. What calculation has been made in respect to a body revolving about the earth ? What facts and suggestions are adduced in support of Pres. Clap's hy- pothesis? What is said of meteorites moving at a greater rat than 420 miles per minute. 1 216 LUMINOUS PHENOMENA. 528. FIFTH HYPOTHESIS. The last hypothesis is that of Chaldni, arid is explained in Art. 555. In this the ignition and explosion of the meteorite are attributed to precisely the same causes as those assigned in the fourth hypothesis. CHAPTER II. OP SHOOTING-STARS AND METEORIC SHOWERS. 529. Shooting-stars or meteors differ from meteorites in several particulars. They commonly possess a supe- rior velocity, and their altitude is generally greater : bursting from the clear sky, they dart along the heaven like a rocket, consuming themselves in their course, and leaving behind a luminous train, which gradually van- ishes in a short time. Unlike the meteorite they usually pass away without any explosion, and no portion of the body ever reaches the earth. Besides, they are far more numerous and frequent ; appearing almost every night, and at times descending in such multitudes that the heav ens are illumined for hours with their glowing trains. 530. ALTITUDE. In order to investigate the phenom- ena of shooting-stars, Brandes and Benzenberg, two German philosophers, made a series of simultaneous observations in the fall of the year 1798. On six even- ings, between September and November, 402 shooting- stars were beheld, and of these twenty -two were so identified, that their altitudes, at the moment of their extinction, could be readily computed. They were found to be as follows : 7 disappeared at altitudes under 45 miles. 9 " " between 45 and 90 miles. 6 above 90 miles. Of what does chapter second treat? In what particulars do shooting-stars and meteors differ from meteorites ? Relate the account of the observations of Brandes and Benzenberg, for determining the altitudes of shooting-stars ? Give their results. SHOOTING-STARS. 217 Tne least and greatest elevations were six miles and wie hundred and forty. 531. In 1823, the investigation was renewed by Brandes, at Breslau and the neighboring towns, on a more extended scale. Between April and October. 1800 shooting-stars were seen at the different stations. Out of this number, 98 were observed simultaneously at more than one station, and afforded the means of esti- mating their respective altitudes. The results were as follows : 4 disappeared at altitudes under 15 miles. 15 " " between \ * and 30 miles. 22 " " " 30 " 45 " 33 " " " 45 " 70 u 13 " " " 70 " 90 " 11 " " above 90 " Out of the last eleven, two vanished at an elevation of 140 miles, a third at 220 miles, a, fourth at 280 miles, and a fifth at 460 miles. The height of four shooting-stars noticed by Profes- sors Loomis and Twining, in December, 1834, varied from 54 miles to 94. 532. Similar observations were made in Switzerland, on the 10th of August, 1838, by Wartman and others. A part of the observers stationed themselves at Geneva, and the rest at Planchettes, a village about sixty miles to the north-east of that city. In the space of seven hours and a half, 381 shooting-stars were seen at Gene- va, and in five hours and a half 104 at Planchettes. All the circumstances attending their appearance were care- fully noted, and their average height was computed at Jive hundred and fifty miles. 533. VELOCITY. In the first series of observations made by Brandes and Benzenberg, only two shooting- stars afforded the means of determining their speed; one possessed a velocity of 1500 miles per minute, and Give those of Loomis and Twining. Give those of Wartman, at Geneva. What is their velocity according to the observations of Brandes aud Benzenberg, and Quetelet ? 10 218 LUMINOUS PHENOMENA. that of the other was between 1020 and 1260 miles per minute. In the second series, undertaken in 1823, the estimat- ed rate of motion varied between 1080 and 2^60 miles per minute. At Belgium, in 1824, M. Qiietelet obtain- ed observations upon six of these singular bodies, from which he was enabled to deduce their respective veloci- ties, which were found to range from 600 to 1500 milea per minute. 534. COURSE. Of'thirty-six stars, whose paths were ascertained by Brandes, the motion in twenty-six cases was downward, in one horizontal, and in the remaining nine, more or less upward ; nor did they always move in straight lines ; for the paths of some were curved. either upwards or sideways ; while others proceeded in a serpentine course. Their general direction was from north-east to south-west. Several examples have been given by Chaldni, where the luminous body described a semicircle, first rising and then falling. 535. MAGNITUDE. The size of shooting-stars is va- riable. Fire-balls, which are regarded as nothing more than large meteors, have sometimes appeared of a magnitude almost incredible. During the remarkable shower of meteors, on the 12th and 13th of November, 1833, luminous globes, apparently as large as Jupiter and Venus, were seen darting through the air in all directions. About three o'clock on the morning of the 13th, a splendid body which appeared equal in size to the lull moon, swept across the heaven from east lowest. Jf the distance of this meteor was only eleven miles, its diameter must have been 528 feet, or one tenth of a mile. Amid the shower of stars that occurred in 1799, meteors were observed by Humboldt, apparently twice the size of the moon. 536. On the evening of the 18th of May, 1839, a meteor of extraordinary magnitude passed over the What is said respecting the course of shooting-stars ? What of their magnitude 1 Reiate the account of the meteor of the 18th of May. SHOOTING STARS. 219" Northern States and a part of Canada. From the facts which he collected, Prof. Loom is estimated its diame- ter at 1320 yards, or three quarters of a mile. Its velo- city was computed by this gentleman to be nearly 2100 miles a minute, its height to be 30 miles, and the length of its path 200 miles. The meteor was followed by a train of inconsiderable extent, probably formed of the detached portions of the body which fell be- hind. 537. SPLENDOR. At times these luminous bodies present a spectacle of surpassing beauty, from their brilliant coruscations, extended trains, and rich diversity of colors. During the month of April, 1832, a globular ball of fire, apparently a foot in diameter, passed over Torhut, in India, early in the morning. Behind it streamed a train of dazzling light, which appeared to be several yards in length. The meteor illumined the surrounding country to a great distance, and after re- maining visible for the space of five seconds, exploded without noise, like a rocket, throwing out numerous coruscations of intense splendor. In May of the same year, and at the same place, a similar body was seen moving rapidly through the air, from north to south. It glowed with a brilliant mixture of green and blue light, and vanished in about three seconds, leaving a luminous train of great length. 538. During the nights of the 9th and 10th of August, 1839, many shooting-stars of singular beauty were seen by Mr. E. C. Herrick, of New Haven. One flashed with a golden green light, and another sparkled with green and blue. Meteors entirely green have at times been noticed. A meteor which swept over Kensington, near London, in 1839, as brilliant as Jupiter and ap- parently of greater size, presented the rare combination of white light in the mass, with one edge red and the opposite of a deep blue or purple. On the morning of the 13th of November, 1833, a most brilliant meteor was seen by Prof. Twining, de- What is said of their splendor r f 220 LUMINOUS PHENOMENA. scending towards the earth with majestic rapidity. Its apparent size was one-fifth that of the moon, and its color a deep red. It vanished when near the ground, leaving behind a fiery train of the same hue, excepting that it displayed the prismatic tints, especially at the point where the meteor expired. 539. The usual color of meteors is that of a phospho- ric white tinged with red. The trains generally vanish in a few seconds, but they have been known to last for the space of seven minutes, and even fifteen. Their light (as we have just seen) is not invariably of one hue, for at times it presents to the eye all the rich tints of the rainbow. METEORIC SHOWERS. 540. The wondrous display of meteors in 1833, drew the attention of philosophers to the subject of shooting stars, and, from the results of subsequent researches and observations, there is now reason to believe, that certain epochs exist when these luminous bodies appear in greater numbers than usual, and that sometimes at the return of these periods they literally descend to the earth in showers. The best ascertained periods are those of the 12th and 13th of November, and the 9th and 10th of August. 541. NOVEMBER EPOCH. On the morning of the 12th of November, 1799, an extraordinary display of this nature was seen by Humboldt and Bonpland, at Curria- na, in South America. During the space of four hours the sky was illumined with thousands of shooting-stars, mingled with meteors of vast magnitude. This phe- nomenon was not confined to Cumana, but extended from Brazil to Greenland, and as far east as Weimar, in Germany. On the 13th of the same month, in 1831. a meteoric ehower occurred at Ohio, and also near Carthagena, ofT the coast of Spain. At the latter place, luminous meteors of large size were beheld, one of which left behind it an Are meteors at all times equally abundant 1 What two great epochs exist ? METEORIC SHOWERS. 221 enormous train, tinted with prismatic hues, its trace con- tinuing visible for the space of six minutes. On the same day of the following- year, vast numbers of shooting stara fell at Mocha on the Red Sea, upon the Atlantic ocean, and in Switzerland. The same brilliant spectacle then appeared in various parts of England ; the sky being illumined soon after midnight by the rushing of thou- sands of meteors in every direction. 542. But by far the most magnificent display of this kind occurred on the night of the 12th and morning of the 13th of November, 1833. It extended from the northern lakes to the south of Jamaica, and from 61 W. Long, in the Atlantic to about 150 W. Long, on the Pacific ocean near the equator. For the space of seven hours, from 9 P. M. to 4 A. M., the heavens blazed with an incessant discharge of fiery meteors, that burst in countless numbers from the cloudless sky. At times they appeared* as thick as snow-flakes falling through the air, as large and as brilliant as the stars themselves ; and it required no vivid imagination to suppose, that these celestial bodies were then actually rushing towards he earth. 543. VARIETIES. The luminous bodies of this shower seemed to be divided into three kinds. The first con- sisted of bright lines traced through the sky, as if by a point. The second of fiery balls, that occasionally darted across the heavens, trailing behind them extend ed and luminous trains, which generally continued visi- ble for many minutes. The third of radiant bodies, that continued almost immovable for a considerable time. 544. Meteors of the first class occurred in great abundance. At Union Town, Pennsylvania, they were seen shooting along like streams of fire with the rapid- ity of lightning ; often crossing half the visible heavens in less than a second. At New York, about a quarter past five o'clock, a meteor of the second class was beheld rushing from the Describe the meteoric showers of November, 1799, 1831, 1832 and 1833* In the shower of 1833 how many kinds of meteors were noticed 1 Describe them, and give the instances. 222 LUMINOUS PHENOMENA. zenith, and marking its course by a fiery line apparently two or three inches wide. After passing downward to a considerable distance, it formed into a ball of the appa- rent size of a man's hat^ and then returning on its path, assumed a serpentine figure. It lay extended through the sky for the space of several minutes, and then struck off to the west. A meteor of the third kind was visible in the north- east, at Poland, Ohio, for more- than an hour. It first appeared in the form of a pruning hook, apparently twenty feet long, and eighteen inches broad, and shone with great splendor. At Niagara Falls, at two o'clock in the morning, an extended luminous body like a square table was noticed in the zenith. It remained for a time nearly stationary, sending out on every side broad streams of light. 545. It was distinctly noticed by many attentive and accurate observers, that all the meteors appeared to emanate from a certain region, situated in the constella- tion Leo ; and that during the whole display this point was stationary among the stars for more than two hoars ; thus proving, that the source of the meteoric shower was beyond the atmosphere of the earth ; for had it been within, it must have moved eastward, in the direction of the earth's daily motion. 546. For four successive years, after the great No- vember shower of 1833, an unusual number of meteors was observed in America at this period. The phenome- non ceased, upon this continent, in 1838 ; but an extra- ordinary display then occurred at Vienna, more than a thousand meteors falling in the course of six hours. 547. AUGUST EPOCH. The second meteoric period occurs on the 9th and 10th of August. It was first dis- tinctly announced in 1827 by Thomas Foster of London, What fact was distinctly noticed by attentive observers ? Where is this point situated ? What is inferred from the circumstance that it was stationary'f For how many years after 1833 did this phenomenon appear 1 When does the second meteoric period occur 1 By whom was it first announced 1 METEORIC SHOWERS 223 in his Encyclopedia of Natural Phenomena. The num- ber of meteors observed at this epoch is probably five or six times more than the usual nightly average, which has been estimated by Mr. E. C. Herrick, of New Haven, at not more than thirty per hour for four observers. 548. From 1836 to the present year, scarcely a season has passed without an unusual display of meteors at thi* period, in some quarter of the globe. On the 9th of August, 1839, four observers at New Haven beheld 691 shooting-stars in the course of fiv. hours, a third part surpassing in brightness stars of the first magnitude. On the ensuing night, 491 were seen in the space of three hours, by the same number of ob- servers ; and at Vienna in Austria, during the same evening, shooting-stars descended at the rate of sixty per hour. Upon the annual return in 1842, 490 meteors fell at Parma in Italy, and 779 at Vienna. Many were like- wise seen at Brussels. At New Haven, in the space of fifty minutes, 89 were seen, one of which equaled Jupiter in splendor. In 1847, at Manlius, N. Y., 415 meteors were seen on the morning of the llth of August in the course of two hours, commencing at midnight and ending at 2 o'clock A. M. On the 10th of August, 1848, 475 meteors were noted at New Haven, in the space of two hours and a half, by Mr. E. C. Herrick and three other observers. Many of them exceeded in brilliancy stars of the first magnitude. In France, on the same night, 414 shooting stars were beheld by two observers, within a period of three hours and a quarter. 549. Like the meteors of November, those of August appear also to radiate from a small space in the heav- ens, which has been referred, by all observers, to the constellation Perseus. Shooting-stars have likewise been found to be more What is said in regard to the recurrence of this shower 1 State facts. What is said respecting the source of the August me'.eors'? Where is it situated 1 224 LUMINOUS PHENOMENA. than usually abundant on the 18th of October, the 6th and 7th of December, the 2d of January, the 20th of April, and from the 15th to the 20th of June. 550. ORIGIN. Prof. Olmsted, who was the first to present his views upon the extraordinary phenomenon, which occurred on the 12th of November, 1833, has ar- rived at the following conclusions from a very extensive examination of facts. That the source of the meteors is a body possibly of great extent, composed of matter exceedingly rare like the tail of a comet. That it revolves about the sun within the orbit of the earth, its period of revolution be- ing probably a little less time than a year, That in consequence of its proximity on the night in question, the extreme parts of the body w r ere detached and drawn towards our globe, by the force of gravity. That its altitude above the surface of the earth, at its nearest point, was about 2238 miles; and that the de- scending fragments entered the atmosphere with a velo- city ranging from about fourteen to twenty miles per second. That these fragments were combustible, and in conse- quence of their amazing velocity, the air was so power- fully compressed before them, that they took fire, and were consumed before reaching the earth. 551. This last conclusion will appear by no means incredible, when the following considerations are taken into view. By suddenly forcing down a solid piston to the bottom of a cylinder, in which it moves air-tight, sufficient heat can be evolved to ignite tinder; and this occurs, when the air within the cylinder is compressed to one-fifth of its original volume. Upon the supposition, that the de- scending fragments compressed the rarefied atmosphere at the height of 35 miles only to the density of common air, the amount of heat developed would be 46,080 What is said of other periods ? Detail Prof. Olmsted' s theory. What is said respecting the amount of heat developed by the condcnsa toot* of *he atmosphere 1 CHALDNl'S THEORY. 225 Fah.; an intensity nearly three times greater than the highest temperature of a glass-house furnace, which is 16,000 Fah. 552. If the nebulous body revolves about the sun in a period somewhat less than a year, it tends to explain the occurrence of shooting-stars at all seasons (since the earth and the nebulous body would then be always com- paratively near each other), and will also favor the ex- planation of the meteoric showers which have happened towards the end of April. 553. Prof. Olmsted has been led to suppose, from the whole course of his observations, that the nebulous body in which the meteors originated, might be identical with the zodiacal light. In a late article published by M. Biot, ihis distinguished philosopher also maintains, that meteoric showers are occasioned by the zodiacal light coming in periodic contact with the atmosphere of the earth. It is not regarded by Prof. Olmsted as essential to the truth of his theory, that a shower of meteors should occur upon the 13th of every November 554. In order to account for shooting-stars in gen- eral, including alike their ordinary and extraordinary displays, and embracing the several epochs, the views of Chaldni have been adopted by Arago and other emi- nent philosophers 555. CHALDNI'S THEORY. This theory consists in supposing, that, besides the planets, millions of small bodies are constantly revolving about the sun, which become ignited when they enter the terrestrial atmos- phere. They are not considered to be uniformly spread throughout space ; but in some regions to be diffusely scattered, and in others grouped together in vast multi- tudes, forming zones or rings around the sun ; many of which cross the path of the earth. The ordinary, nightly phenomenon of shooting-stars. If the nebulous body revolves about the sun in a little less time than a year, what does it tend to explain 7 What is M. Biot's opinion! What is Chaldni's theory 1 10* 226 LUMINOUS PHENOMENA. is then imagined to arise, when the earth, in her pro- gress through the heavens, traverses those regions which contain only a. few of these bodies ; but when the zones are encountered, and the globe passes amid countless numbers, the display is proportionally greater, and the meteors occasionally descend in magnificent showers. Amid this vast collection solid masses of considerable size are supposed to exist, and should one of these enter the atmosphere of the earth, a meteorite with all its splendors sweeps across the sky. Such at present is the general state of our knowledge in regard to shooting-stars. CHAPTER 1IT. OF THE AURORA BOREALIS OR NORTHERN LIGHT. 556. THE Aurora Boreal is is a luminous appearance in the northern sky, which presents, when in full dis- play, a spectacle of surpassing splendor and beauty. It has in all ages been an object of wonder and mystery, and still continues so ; for although many valuable facts have been brought to light by the investigations of science, the cause of this brilliant phenomenon is yet in- volved 111 obscurity. 557. CONSTITUTION. Notwithstanding its fantastic motions, and momentary changes in brightness and color, the aurora, according to the best observations, still preserves, amid all its fluctuations, certain invaria- ble characteristics of form and position. It consists of a dark segment, an arch of light, luminous streamers, and a corona or crown. 558. DARK SEGMENT. All observers in the high latitudes of Europe, agree in stating, that before the What does chapter third treat of? What is the Aurora Borealis 1 Of what does it consist 1 Describe the dark segment. DARK SEGMEN'T. 227 aurora appears, the sky in the northern horizon assumes a darkish hue, which gradually deepens, until a circular segment is formed, bordered by an arch of light, extend- ing from east to west. The segment presents the ap- pearance of a cloud, its tint is light in the lower lati- tudes, and grows darker as we advance to the north, up to a certain limit ; after this the reverse occurs, and when high latitudes are attained it becomes so faint as to be scarcely visible. At Upsal and Christiana it is some- times black or of a deep gray, which changes into a violet. During a splendid aurora, that occurred at Toronto in. Dec. 1835, and which is described by Capt. Bonnycastle, a dark, black changing mass, was visible below the lu- minous arch, (fig. 42.) and in a remarkable phase of the aurora, when several bright bows were seen at once, the interval between the second and third assumed a blackness of the deepest intensify. Fif.42. AURORA SEEN AT TORONTO. 559. A difference of opinion exists in regard to the nature of this segment. From numerous observations made at Dorpat in Russia, Struve infers, that the dark- Is it real or imaginary ? 228 LUMINOUS PHENOMENA. ness is simply the effect of contrast with the luminous arch ; while, from equally extensive researches at Abo in Finland, Argelander concludes, that the segment is something real ; since the portion of the sky it occupies, is darker than common, before the bright bow of the aurora appears. 560. ARCH OP LIGHT. The dark segment is bounded by a luminous arch or bow, varying in width from one to three apparent diameters of the moon. Its lower edge is clearly denned, but the upper is only so when the arch is narrow, for as the width increases, it gradually blends with the brightness of the sky. The color of the bow is a pale white, which becomes more pure and brilliant near the polar regions. According to the most accurate observations, this arch has a tendency to place itself at right angles to the magnetic meridian, or in other words, to the direction of a compass-needle at rest. (C. 985.) This fact was particularly noticed by Lieutenant Hood, who accom- panied Franklin in his northern expedition in 1819. 561. The centre jf the auroral arch probably coin- cides with the north magnetic pole of the earth, which is situated in 70 N. Lat. In our own country, the com- pass-needle points to the north, and the arch crosses the heavens from east to west ; but in some parts of Green- land, the needle is directed to the ivest, and the arch is then seen extending from north to south. In the year 1838, when Simpson wintered at Fort Confidence, in 66 54' N. Lat., he found the needle always pointing to the north-east, and the auroral arches invariably spanning the heavens at right angles, from north-west to south-east. At Melville Isle, in 74 30' N. Lat., the luminous arches were seen by Parry in the south; the north magnetic pole of the earth being then in that direction. 562. Tiiis beautiful bow of light is not stationary, Describe the arch of light. Its color and position. What is its position in some parts of Greenland ? What was its position at Fort Confidence and at Melville Isle? Is the arch of light stationary? ARCH OF LIGHT. 229 but frequently rises and falls; and when the aurora ap- pears in great splendor, several arches are seen at the same time crossing the sky, ascending gradually from the horizon to the zenith, and passing over in succession with their summits moving in or parallel to the magnetic meridian ; presenting to the eye broad belts of light, increasing in brightness as they approach the zenith. 563. No less ih&ufive such arches were seen at once by Lieut. Hood ; but similar phenomena, of far greater beauty, were witnessed by M. Lottin at Bossekop, in West Finmark, during the winter of 1838-9. (Figs. 43, 44.) Fig. 43. AURORA SEEN AT BOSSEKOP. Fig. 44. AURORA SEEN AT BOSSEKOP. What phenomena were beheld by Lieut. Hood and M. Lottin '* 230 LUMINOUS PHENOMENA. On one occasion, as many as nine auroral arches were visible, separated by distinct intervals, and in their arrangement resembling magnificent curtains of light, hung one behind and below the other, their dazzling folds extending completely across the sky. 564. STREAMERS. Although the luminous arch pre- serves, in the main, its curved form, it is subject to con- stant changes. Now at one extremity, now at the other, and again at intermediate points, a cloud of light will break suddenly forth, separating into rays which stream upward like tongues of fire, moving at the same time backwards and forwards, along the auroral bow. The origin of the streamers is in the luminous arch, from which they rise in the form of tapering rays or pencils of light, ever in motion, and continually varying in brilliancy, number, magnitude, and color. At one moment, a ray is just visible above the arch, faintly glowing in the sky ; at the next it is seen shooting up- ward in a pyramid of flame and at the same time moving majestically across the heavens. As suddenly its bright- ness fades, and as quickly it is again beheld, flashing forth with renewed splendor. 565. COLOR. During the extraordinary displays of the aurora in our own latitude, the sky is frequently seen suffused with a flush of rosy light, while the streamers assume a crimson hue. In that which oc- curred on the night of the 14th of November. 1837, the upper extremities of the streamers were of the deep- est scarlet, while below they were brilliantly white. But the richest tints appear in the arctic regions. In the auroras witnessed at Bossekop, the rays, at their base, glowed with a blood-red hue, the middle was of an em- urald green, and the rest of a pure transparent yellow. During a brilliant display that occurred at ^ort Con- fidence, on the 5th of March, 1839, the rays were tinged with red, purple, and green. 566. CORONA OR CROWN. The vivid rays that dart What is said in regard to the streamer?, their origin and color 1 CORONA. 231 forth from the luminous arch not unfiequently unite at a point near the zenith; forming a brilliant mass of light which is called the corona or crown. The aurora then appears in its greatest splendor ; the sky resembles a fiery dome, and over the streamers, which seem like pillars of variegated flame supporting the corona, radiant waves and flashes of light pass in quick succession. The luminous columns at this time are apparently shaken and wave with a tremulous motion ; whence they have received, under these circumstances, the name of merry dancers. At Bossekop, this radiant wave was seen by Lottin, crossing and re-crossing with rapid undulations the whole broad field of auroral light. These coruscations are generally attended with color. 567. When, in the northern hemisphere, a needle is delicately balanced upon a horizontal axis, its north end immediately dips downward upon its being magnet- ized. Such an instrument is called the dipping-needle. (C. 998.) The streamers of the aurora assume the same direction as the dipping-needle, and are parallel to each other ; hence the corona is not formed by any actual union of the streamers near the zenith. It arises from an optical illusion. When we look across an extensive field of corn, the rows, at their remote ends, seem to ap- proach each other, as if converging to a point ; though we know that they are three or four feet apart, through- out their whole distance. In like manner when we gaze at the auroral streamers with their bases at the horizon and their summits at the zenith, they will in like manner apparently converge to one point, forming the corona, whose centre is in the line of the dipping-needle. 568. Within the dark segment streamers of the same color are frequently seen, rising and falling like columns of smoke, changing their hue in a moment, and possess- ing all the motions of the luminous rays. Like the ,_. .... " 'i Describe the corona. When does it appear 7 How is it formed ? What is observed within the dark segment 1 232 LUMINOUS PHENOMENA. latter, their line of direction is parallel to that of the dipping-needle. 569. EXTENT. The aurora is not a local appearance, for it is heheld simultaneously in places widely separa- ted from each other. Thus, on the 5th of January, 1769, the same aurora was seen in France and Pennsyl- vania ; and a magnificent display occurred on the 7th of January, 1831,, which was visible at Lake Erie, and throughout northern and central Europe. Another aurora, that happened on the 3d of September, 1839, was seen at the Isle of Sky, 57 22' N. Lat., at Paris, New Haven, and at New Orleans. 570. The beautiful phenomenon of the northern light is not confined to the northern hemisphere. An aurora australis, or southern light, was observed by Don Ulloa, at Cape Horn, in 1745 ; and various displays were seen by Capt. Cook, in the high southern latitudes, at the same time that the northern lights were visible in Eu- rope. In the late Exploring Expedition, during the southern cruise of the Peacock and Flying Fish, several brilliant auroras were seen, which are thus recorded. On the 18th of March, 1839, there was " a beautiful display of the aurora australis, extending from S. S. W. to the east ; the rays were of many colors, radiating towards the zenith and reaching an altitude of 30. On the 19th, in about 68 S. Lat., another display was wit- nessed which exhibited a peculiar effect. In the south- ern quarter of the heavens there was the appearance of a dense cloud, resembling a shadow cast upon the sky, and forming an arch about 10 in altitude. Above this ' were seen coruscations of light, rendering all objects around the ship visible. From behind this cloud, diverg- ing rays frequently shot up to an altitude of from 25 to 45. These appearances continued until the day dawned." What is said of the extent of the aurora 1 Are auroras seen in the southern hemisphere ? Whut are they called ? Give instances. HEIGHT. 233 571. HEIGHT. The height of the aurora has been variously estimated The earlier philosophers computed its altitude at several hundred miles ; but a much lower limit is assigned by later observers. An aurora which appeared in March, 1826, at different places in England, was calculated by Dr. Dalton to be 100 miles high. Observations for determining the elevation of the splen- did aurora of January 7th, 1831, were made by Christie and Hansteen, but their computed heights varied from 23 miles to 120. In the brilliant display that happened on the 14th of November, 1837, the estimated altitudes were even more discrepant, varying from one to two hundred miles. A very distinct auroral arch was seen at various places throughout the Northern arid Middle States, at about ten o'clock on the night of the 7th of April, 1847. From the observations taken by Mr. E. C. Herrick, at New Haven, Ct., and Dr. P. W. Ellsworth, at Hartford, Cu, the height was computed by the former gentleman, and found to be one hundred and ten miles. These observations having been made under favorable circum- stances, and being accordant with each other, this re- sult is entitled to great confidence. The height of the northern lights is obtained in the way that has been already described ; but such is their fitful nature and varying form, that two distant observers can scarcely ever be sure that they have measured the angular height of the same part of the aurora. Hence arise these discordant calculations upon the same phe nomenon. 572. There is every reason for believing, that the auroral light is at times very near the earth, and even within the region of the clouds. During the polar expedition of Franklin, in 1820, ob- servations were taken by Hood and Richardson, upoi? thiee auroras, at stations eighteen leagues distant from each other, and the heights which they obtained, were found to vary from six to seven miles ; while an aurora Relate in full the calculations respecting the height of the northern lighta LUMINOUS PHENOMENA. beheld by Farquharson, of Scotland, was computed to be as low as 4300 feet. Franklin thus remarks : " The fact that the aurora exists at a less height than that of dense clouds, was evinced at Fort Enterprise, on two or three occasions, during the night of the 13t,h of February, 1821, and particularly about midnight, when a brilliant mass of light, variegated with the prismatic colors, passed between a uniformly steady, dense cloud and the earth. In its progress, that portion of the cloud which the stream of light covered was completely concealed until the coruscation had passed over it, when it appeared as before." 573. A similar, but more extraordinary phenomenon, which occurred during his third Arctic voyage, is thus related by Capt. Parry. " While Lieutenants Sherer, Ross, and myself were admiring the extreme beauty of the northern lights, we all simultaneously uttered an exclamation of surprise, at seeing a bright ray of the aurora shoot suddenly downward from the general mass of light, and between us and the land, which was there distant only three thousand yards. I have no doubt, that the ray of light actually passed within that dis tance of us." 574. SOUNDS ATTENDING THE AURORA. It has been asserted, that the aurora is sometimes accompanied by a noise like the rustling of silk, or the sound of a fire when excited by the wind ; but much difference of opinion has arisen upon this point. Those who are incredulous in this particular, affirm that the noise in question may be nothing more than the murmur of the ocean, or of the forest ; the rustling of the snow as it is iriven by the wind, or the crackling sound that arises from its freezing ; all which, it is said, might be easily attributed to the aurora, vt hen the mind is excited by the wondrous spectacle, and susceptible to every illusion . the splendors that burst upon the sight, and the sounds which strike the ear being then referred to the same origin. State the facts showing that the aurora is at times very near the earth. Give the facts respecting the sounds attending the aurora. AURORAL SOUNDS. 235 575. Scoresby, Richardson, Franklin, Parry and Hood, during their Polar expeditions, never heard any sound which they considered as proceeding 1 undeniably from the notthern lights, though hissing noises were heard during the auroral displays which were attributed by them to one or more of the preceding causes. These observers do not, however, deny, that at times audible sounds proceed from the aurora, and even express such a belief, founded upon the concurrent testimony of the natives of the arctic climes. 576. Credible observers in Iceland, Siberia, and Scandinavia, have never heard these singular sounds ; nor were they perceived by the French scientific expe- dition, which wintered at Bossekop, in 1838-39 ; but Hansteen claims to have established their existence from a series of observations in the high northern latitudes. Upon this subject, Simpson thus remarks in his North- ern Discoveries when speaking of a brilliant aurora seen by his attendant, at Fort Confidence, on the 5th of March, 1839, " The aurora seemed to ascend and de- scend, accompanied by an audible sound resembling the rustling of silk. This lasted about ten minutes, when the whole phenomenon suddenly rose upwards, and its splendor was gone. Ritch is an intelligent and credible person, and on questioning him closely, he assured me that he had perfectly distinguished the sound of the aurora from that produced by the freezing- of the breath, for the temperature was forty-four degrees below zero. I can therefore no longer entertain any doubt of a fact uniformly asserted by the natives, and insisted on by my friend Mr. Dease, and by many of the oldest resi- dents of the fur countries, though I have not had the good fortune to hear it myself." 577. TIME. The appearance of the northern lights is not confined to any particular hour of the night, a fact which is fully proved by the circumstance that the same display is frequently witnessed at places widely differing in longitude. Thus, if the aurora extends Does the aurora appear at any particular hour 1 LUMINOUS PHENOMENA. from Boston, Mass., to Berlin, in Germany, and is be- held simultaneously at these cities, the difference in the reckoning of time will be n early five hours and a half (C. 939). 578. There is much reason for believing that the aurora sometimes occurs during the day, though rendered invis- ible by the presence of the sun. Richardson perceived at Bear Lake, the motion of the aurora before the entire disappearance of twilight, and even during the day he discerned clouds, arranged in columns and arches, resem- bling those of the northern lights. Besides, as we shall show hereafter, a brilliant display of this phenomenon is always accompanied by a greater or less disturbance of the magnetic-needle, (C. 997,) and as these disturb- ances take place in the day as well as in the night, it is reasonable to infer that they are caused by the presence of an invisible aurora. 579. FREQUENCY. This phenomenon is more fre- quently seen in winter than in summer ; we must not, however, hastily conclude from this circumstance, that the number of auroras during the former season is actu- ally greater, for the increased length of the nights du- ring the winter would enable us then to see more dis- plays of the northern light, even if the times of its occur- rence were equally distributed throughout the year. About the period of the equinoxes they also appear to be more frequent. These facts are shown from the follow- ing table of Kaemtz, which gives the number of auroras that have been seen in each month. NUMBER OF AURORA BOHEALES IN EACH MONTH. January, 229. July, 87. February, 307. August, 217. March, 440. September, 405. April, 312. October, 497. May, 184. November, 285. June, 65. December, 225. Why is it supposed sometimes to occur i the day 7 What is said respecting the frequency jf its appearance in winter and ummer? Recite the table. FREQUENCY. 237 580. In addition to this annual variation, there ap- pears to be another which extends through a consider- able number of years, but of which very little is known. Thus, from 1707 to 1752, the northern lights became more and more frequent ; but after the latter date, a period of twenty years occurred, in which they dimin- ished in number. An increase in their frequency began in 1820, and since that period many magnificent displays have been witnessed. The number observed for the last ten years, at New Haven, Ct, by Mr. E. C. Herrick, is shown in the fol- lr wing table. Number of Auroras From May, 1838, to May, 1839, 35. it 1839, tt 1840, 36. a 1840, ti 1841, 36. it 1841, n 1842, 21. et 1842, a 1843, 7. it 1843, tt 1844, 7. a 1844, it 1845, 12. tt 1845, ti 1846, 19. it 1846, it 1847, 20. a 1847, n 1848, 28. Between the 12th of September, 1838, and the 18th of April, 1839, no less than one hundred and forty-three distinct auroras were seen by the French observers at Bossekop. They were most frequent at the period when the sun was below the horizon, viz. : from the 17th of November to the 25th of January. During this night of ten weeks, sixty-four auroras were visible. 581. DISTURBANCE OF THE MAGNETIC-NEEDLE. During the prevalence of the aurora, the compass-needle, instead of remaining motionless, in the magnetic meridi- an, is often much disturbed. Sometimes "it is deflected toward the east several minutes and even degrees ; then Is there any other probable variation 1 Recite the table. What is said respecting the disturbance of the compass-needle 7 238 LUMINOUS PHENOMENA. it is agitated, and returns either slowly or rapidly, to the meridian, which it passes at times and moves toward the west. These deviations are as changeable as the phenomenon itself. When the arch is motionless the needle is quiet ; its disturbance commences when the streamers begin to play. 582. Franklin observed at Fort Enterprise, that the disturbance of the needle was simultaneous with some change in the/orra or action of the northern lights, and that after being deflected it returned to its former posi- tion very gradually, not resuming it before the follow- ing morning, and sometimes even not before noon. Moreover when the auroral arch was either at right angles to the meridian, or its western extremity north of west, the needle was deflected toward the west ; but if its western extremity was south of west, the needle moved toward the east. During the aurora of November 14th, 1837, the en tire range of the needle at New Haven, was observed by Messrs. Herrick and Haile to be nearly six degrees. It was not until the morning of the next day, between seven and nine o'clock, that the needle was at rest in its usual position. 583. This effect upon the magnetic needle during the prevalence of the northern lights, was noticed for the first time by Celsius and Hiorter, at Upsal, on the 1st of March, 1*741. 584. It is asserted by Wilke, that when the aurora appears in great splendor, the position of the dipping-- needle is as variable as that of the compass-needle ; the former rising zn& falling with the northern crown. Hansteen has also observed, that the dipping-needle descends very much below its usual position before the aurora is visible ; but that after the display commences it begins to rise: and more rapidly in proportion to its brightness. The needle then slowly resumes its origi- nal position, which it frequently does not attain unu3 How great was its range at New Haven, November 14th, 1837? What has been observed respecting the dipping-needle? CAUSE. 239 twenty-four hours have elapsed. From numerous ob- servations at Bossekop, M. Bravals has likewise obtained the same results. 585. CAUSE. No satisfactory explanation has ever been given of this singular phenomenon : that a connec- tion exists between the aurora and the magnetism of the earth, is evident from the preceding facts ; but the nature of that connection is still unknown. To trace all the hypotheses which have been started would be an unprofitable task ; but a glance at some of the most prominent may be given. Canton supposes the aurora to be caused by the passage of electricity from positive to negative clouds, in the upper and rarefied regions of the atmosphere. He adduces in support of this view the fact, that when the air within a long, glass tube is rarefied, and electricity passed through it, the whole tube is illumined by flashes of light traversing its entire length. It may, however, be stated in reply, that the general height of the northern lights far exceeds that of the highest clouds. 586. Beccaria supposes, that there is a constant cir- culation of the electric fluid from north to south, and that the aurora is seen, whenever the electrical current passes nearer than usual to the earth, or the state of the atmosphere is such as to vender it luminous. Faraday has demonstrated, that the electricity of the earth neces- sarily tends from the equator towards the poles ; and has suggested, that the aurora may possibly arise from an upward current in the atmosphere flowing back from the poles towards the equator. Kaemtz conjectures, that since a spark is perceived every time an electric current produced by a magnet is broken, the northern lights may perhaps be caused by a rupture in the magnetic equilibrium of the globe. At the same time, however, he utterly disclaims the idea of ac- counting for all the circumstances of this wonderful phe- nomenon, in our present imperfect state of knowledge. What is known of the origin of the northern lights 7 State the hypotheses givea. &10 LUMINOUS PHENOMENA. 587. UTILITY. The light of the aurora, from its fre- quency and splendor, serves materially to relieve the darkness and enliven the gloom of the long polar night. During this period, its play is almost, incessant, (Art. 580,) and its coruscations exceedingly vivid and beautiful. So brilliant is the aurora in these regions, that Mau- pertius and others, who were sent to Lapland in 1735, by the Academy of Sciences of Paris, for the purpose of measuring an arc of the meridian, were enabled to pur- sue their difficult work by the light it afforded, long after the sun had ceased to be visible. And Maupertius remarks, that its light, together with that of the moon and stars, is sufficient, during this season, for most of the occasions of life. What useful purpose does the aurora subserve in the polar regions? PART VII. MISCELLANEOUS PHENOMENA CHAPTER I. 3F THE FALL OF TEREESTRIAL SUBSTANCES FOREIGN TO THE ATMOSPHERE. 588. IN addition to storms of rain, hail, and snow, which are products peculiar to the atmosphere, and are the results of the operations of well -known agencies and laws, showers of matter of a terrestrial nature have not (infrequently occurred, which have been traced, upon close examination, to a mineral, vegetable, and even animal origin. The most remarkable of these singular phenomena are dust-storms and Hood-rains, which will now be de- scribed. DUST-STORMS AND BLOOD-RAINS. 589. From time to time, and in regions of the globe widely separated from each other, dust in large quantities has descended from the heights of the atmosphere, not only upon the land, but also far out on the ocean, hundreds of miles from the shore. It is entirely distinct from that which is disseminated through the air by the winds, during the eruption of volcanoes, and for many years has been described, by observers and writers, under the various names of dust-storms, dust-rain, red fogs, Sirocco dust, "What is the subject of part seventh 1 Of what does this chapter treat 1 ? la addition to storms of rain, hail, and snow, what other kinds of showers have not unfrequently happened 1 What are the moat remarkable of these phenomena 1 "What is said respecting the fall of dust from the heights of the atmo- sphere 1 What are the various names under which this phenomenon has been described 1 11 242 MISCELLANEOUS PHENOMENA. African dust, sea-dust, Atlantic dust, and tradewind- dust. 590. This dust not only falls dry, in the form of a fine, impalpable powder, but is occasionally mingled with rain, hail, and snow, which it dyes with its own hue. As it is usually of a reddish color, these showers of rain and storms of hail and snow have received the appellation of Hood-rains. DUST-STORMS. 591. INSTANCES. On the 20th of October, 1755, a Mack dust, like lamp-black, fell in Shetland, between 3 and 4 o'clock in the afternoon. The sky at the time was hazy, and the dust fell in such quantities as to cover the hands and faces of persons exposed to it, and to black- en their linen. 592. During the 5th and 6th of March, 1803, while the wind was blowing from the south-east, a shower of .red dust fell in Italy. Ten years afterwards, on the 14th of March, 1813, a similar storm occurred at the town of Gerace, in Calabria. According to Prof. Sementirii, of Naples, the wind, in the early part of the day, blew from a western quarter, bringing up dark, heavy clouds from the sea over the land. At about 2 o'clock in the afternoon the wind sub- sided, while a deep gloom pervaded the air, and the clouds grew red and threatening. Thunder followed, and soon after red dust, mingled with red rain and snow, descend- ed upon the town. This dust had the appearance of a fine powder. 593. A shower of dust fell at Malta on the 15th of May, 1830, and at the same time a similar fall occurred in the bay of Palmas, in Sardinia, while a Sirocco wind was blowing from a south-easterly quarter. The Maltese dust was of a brownish-red hue. Some of it wan collected by Mr. R. G. Didman, of the ship Revejj^e, and for- "What are blood-rains, and why are they so called * Relate the various instances given of dust-storms in Shetland. Italy, Gerace, Malta, and Genoa. DUST-STORMS. 243 warded to Mr. Charles Darwin, an eminent English nat- uralist, for examination. 594. On the 16th of May, 1846, a shower of Sirocco- dust occurred at Genoa, having the same brownish-red hue as the dust which fell at Malta in 1830. Six months afterwards a remarkable storm of this nature swept over Lyons, in France, and so thickly did the dust descend, that the amount which fell at this time was com- puted to weigh no less than thirty -six tons. 595. In the year 1831, the ship Beagle, under the command of Captain Fitzroy, was dispatched by the British government on a voyage of scientific discovery around the world. Mr. Darwin, the naturalist just men- tioned, accompanied the expedition, and during the voyage observed a dust-shower, near St. Jago, the chief of the Cape de Verd isles. The morning before the Beagle anchored at Port Praya, in St. Jago, Mr. Darwin collected a little package of im- palpable brown-colored, dust, which appeared to have been filtered from the wind by the gauze of the vane at the mast-head. In speaking of this phenomenon, he re- marks, that the atmosphere in this region is usually filled with a haze, caused by the falling of this fine, brown- colored dust. By the kindness of a friend, Mr. Darwin received four parcels of dust which fell upon the deck of a vessel, a few hundred miles north of the Cape de Verd isles. 596. Much valuable information respecting dust-show- ers on the ocean has been gathered by this gentleman, who has found fifteen different accounts of the descent of dust upon ships when far out on the Atlantic. It has often fallen upon them when they were several hundred, and even a thousand miles from the coast of Africa, and at points sixteen hundred miles distant in a north and south direction. 597. In some of the dust collected upon a vessel three 'hundred miles from land, particles of stone were discov- State what is said respecting the fall of dust on the ship Beagle. What is known, from the researches of Mr. Darwin, in regard to th Atlantic dust 1 244 MISCELLANEOUS PHENOMENA. ered, more than the thousandth of an inch square, mixed with finer matter. It falls in such quantities as to soil every thing upon which it descends, and to irritate the eyes of persons exposed to it. Ships have even been known to run ashore, owing to the obscurity of the atmo- sphere resulting from the presence of this dust. 598. The occurrence of dust-showers in the vicinity of the Cape de Verd isles has been noticed, at intervals, from the year 1579 to the present time. The extent of the region over which they here prevail varies, according to Darwin, from 960,000 to 1,280,000 square miles ; but a greater estimate is given by Captain Tuckey, who sup- poses that it ranges from 1,648,000 to 1,854,000 square miles. The Atlantic dust is believed by Mr. Darwin to come from Africa, since not only does wind blow from that quarter whenever it falls, but the showers also occur during those months when the harmattan is known to raise clouds of dust high into the atmosphere. 599. During a voyage from Richmond, Va., to Rio Janeiro, in the winter of 1845-6, Mr. Thomas Ewbank, of the U. S. Patent Office, met with many instances of the falling of sea-dust, and traced the rich and peculiar hues, that at times adorned the clouds and sky, to the diffusion of this fine powder throughout the intermediate atmosphere. 600. On the 10th of January, 1846, in 23 33' N. Lat., and 34 37' W. Long., he observed a narrow belt of slate- colored sky skirting the horizon, while upon this rested a broad band of vermilion, interspersed with soft dashes of Indian ink, shaded with umber. These hues changed, by insensible degrees, into a bright cream-color, and this again into a pale, delicate green, which deepened in tint as it approached the zenith, while over all floated aniber- Ctforxl clouds, growing richer in hue and smaller in size as viey sunk towards the horizon. What is the extent of the region over which the Cape de Verd and Atlantic dust-storms prevail ] What is the opinion of Mr. Darwin as to the origin of this dust? Relate in full the account given by Mr. Ewbank of the dust-storm* that he observed on a voyage from Richmond to Rio Janeiro. BLOOD-RAINS. 245 601. Three days afterwards, in 16 07 X N. Lat., and 31 13' W. Long., the wind blew strongly from the east, bearing along with it a red, impalpable powder. This minute dust was seen on the windward side of the sails, where it was supposed to have been collecting during the two previous days. It was extremely fine, and could only be seen by bringing the loose fibres of a rope, upon which it had settled, between the eye and the sun, when its presence and color were readily discerned. 602. The sun throughout the day, as well as the moon at night, was enveloped in a haze, which was supposed to be caused, in some measure, by the dust that floated in the air. The captain of the vessel, who had noticed this phenomena before, called the red powder African sand. 603. During the two following days the heavens pre- sented scenes of gorgeous and surpassing beauty, the colors of the sky and clouds ranging through emerald green, pink, purple, crimson, yellow, chocolate, umber, and slate ; while beneath this rich and varied combination a groundwork of the purest cream-color extended, giving tone to the whole, and changing in tint from a fawn-color to a pale white. 604. On the 16th of January, in 7 44' N. Lat., and 28 31' W. Long., the red dust was observed to accu- mulate upon the vessel an old sail, looking as if it had been painted of a light brick color. The ship at this time was opposite Soudan*and Senegambia, which border on the great African desert, whence the captain supposed the shower to come. A portion of the dust was collected by rubbing a piece of foolscap paper over the colored sail. 605. A fall of dust, accompanied by snow, occurred in the month of February, 1850, at Olsterholz, near Det- mold, in Westphalia. The wind, during this phenomena, blew from the south-west. The dust fell so thickly as to cover the earth to the depth of one eighteenth of an inch. BLOOD-BAINS. 606. INSTANCES. On the 12th of August, in the year What is said of the dust-shower that occurred at Olsterholz ? 246 MISCELLANEOUS PHENOMENA. 1222, a red rain fell at Rome for the space of a day and a night j and a similar event occurred at Cremona on the 3d of July, 1529. In 1608 a red rain descended for several miles around Aix, in France ; and in 1623 an- other blood-rain happened at Strasburg, between 4 and 5 o'clock in the afternoon. On the 5th and 6th of May, 1711, red rain fell at Orsio, in Sweden ; and a shower of this nature also occurred near Genoa in the year 1744. 607. A very remarkable rain of this character fell at Locarno, in Switzerland, on the 14th of October, 1755. A warm Sirocco wind was here blowing at 8 o'clock on the morning of this day, and two hours afterwards the air was filled with a red mist. At 4 o'clock in the afternoon a blood-rain descended, which left on the ground a reddish deposit. Nine inches of this colored rain fell, in the course of one night, over a region forty square German leagues in extent. It even reached Suabia, on the northern side of the Alps ; while amid the cold heights of these lofty mountains it changed into a reddish snow, which fell to the depth of nine feet. 608. The red matter that was deposited during this shower was found, by actual measurement, to be in some places an inch deep, or one-ninth part of the quantity of rain. Upon the supposition that it fell, on an average, to the depth of only one-sixth of an inch, twenty-seven hundred cubic feet of this red substance must have cov- ered every English square mue. 609. On the 13th of November, 1755, a red rain fell in Russia, Sweden, Ulin, and on the Lake of Constance ; ar.d on the 9th of October, 1763, a similar shower de- scended at Cleves, Utrecht, and many other places ia Europe. 610. During the remarkable phenomenon that occurred ft* Gerace, on the 14th of March, 1813, the red rain pre- vailed over a great extent of country, falling throughout the two Calabrias, and on the opposite side of the province of Abruzzo, in the kingdom of Naples. Relate, in detail, the several instances given of the fall of blood- rain. BLACK RAIN. 247 611. A red rain likewise fell at Sienna, and upon the adjacent country, on the 15th of May, 1830, at 7 o'clock in the evening, and also at midnight. The weather for" two days previously had been calm, but the sky was over- cast with dense, reddish clouds. 612. BLACK RAIN. The material that mingles with these extraordinary rains is not always of a red hue, but is sometimes of a dark color, and imparts an inky Hack- ness to the shower. A rain of this kind occurred at Montreal, in Lower Canada, on two several days during the month of November, 1819, under the following cir- cumstances : On the morning of the 21st of this month a dense gloom enveloped the city, while the whole atmosphere was obscured by a thick haze, of a dusky orange color, and at this time rain descended of a dark inky hue. The weather soon after became pleasant, and continued so until the following Tuesday, when at noon the whole city was again shrouded in a heavy, damp vapor, so dense that it became necessary to light candles in all the houses. At about 3 o'clock in the afternoon a slight shock of an earthquake was felt, attended by a noise like the discharge of distant artillery. Soon after, when the darkness was the deepest, the gloom was dispelled by a vivid flash of lightning, which was followed at once by a crashing peal of thunder ; and this was succeeded by a heavy shower of thick, Hack rain. 613. On the 22d of April, 1846, a copious Hack rain fell also in England, in the towns of Dudley, Stonrport, Abberly, and Bewdley, which are situated in the ncrtlicrn part of Worcestershire. This shower lasted from 11 o'clock in the morning till 1 o'clock in the afternoon, the rain descending so abund- antly as to Hacken the waters of the placea where i* fell, and darken the river Severn. Gire an account of the black rain of Montreal. Of that which happened iu Worcestershire. 248 MISCELLANEOUS PHENOMENA. 614. RED HAIL. A storm of red hail is stated b? Baron Humboldt to have once occurred at Paramo, in South America, between Bogota and Popayan. There hkewise fell over all Tuscany, on the 14th of March, 1813, a shower of hail of an orange hue. 615. BLACK HAIL. A hail-storm happened in Ireland on the 14th of April, 1849, which deposited upon the ground a black, inky substance. Some of this dark mat- ter was collected and examined, and found to be of the same nature as the coloring material of red rains. STORMS OF COLORED SNOW. 616. RED SNOW. One of the most remarkable falls of red snow on record is that which has already been mentioned (Art. 607), as occurring simultaneously with the blood-rain of Locarno, in Switzerland, when snow of a reddish hue covered the neighboring Alps to the depth of nine feet. 617. On the 5th and 6th of March, 1808, red snow fell for the space of three nights in Carniola, a province of Germany, and throughout Carnia, Cadore, Belluno, arid Feltri, to the depth of jive feet and ten inches. The earth had been previously covered with white snow, and the storm of colored snow was succeeded by another, the flakes of which were as usual, of a pure and brilliant white. The two kinds were perfectly distinct. When a portion of the red snow was melted in a vessel, and the water evaporated, a fine rose-colored, earthy sediment remained at the bottom. Red snow, likewise, fell at this time on the mountains of the Valtelline, in Switzerland, at Brescia, and on the Tyrol. 618. During the dust- shower and Hood-rain, at Ge- race, red snow descended over a wide extent of country, embracing the two Calabrias, Tolmezzo, and the Carman Alps. In Tuscany it fell of an orange hue, while al Bologna its tint was a brownish yellow. "What instance is given of the occurrence of red haill What of Hack haill Where, when, and under what circumstances have storms of colored now occurred ! NATURE OF THE DUST. 240 619. On the 15th of April, 1816, colored snow fell in Italy, upon Tonal, and on other mountains. It was of a brick-red hue, and, when melted and evaporated, a light and impalpable earthy powder remained. 620. A storm of reddish snow took place on the 31st of March, 1847, in Puster Valley, in the Tyrol. It de- rived its tint, which was a brownish red, from a fine colored dust, resembling that of the Atlantic showers. 621. BLACK SNOW. A few years ago a fall of Hack snow occurred in New Hampshire, at Walpole, and the adjoining towns. A person writing to the Boston Journal from Walpole, remarks, in relating this extraordinary phenomenon : " I send you some writing, written with the snow as it fell, and with a clean pen." This writing, according to the editor of the Journal, vt&$ perfectly leg- ible, and appeared as if having been written with palt, Hack ink. 622. These colored snows must not be confounded with those already described in Arts. 286, 287, and 288. The snows there mentioned are white before their fall, and acquire their red and green tints, after their descent, from the presence of a microscopic plant whose cells are filled with animalcules, and which, even in Arctic climes, spreads itself with extraordinary vigor over fields of snow. On the contrary, in storms of colored snow, the coloring matter is in the atmosphere, and the snow is dyed before itsfall. NATURE OF THE DUST. 623. It appears from the microscopic investigations of eminent observers, and especially from those of Ehrenberg, that the dust which causes dust-storms, and produces the phenomenon of blood-rains, is composed both of organized and unorganized matter : the latter being pwtions of various minerals, while the former consists principally of the shells of infusoria, mingled with fragments of pet- rified plants &nd parts of insects. Are these colored snows the same in character as those already <3e- cribed in Arts. 286, 287, and 288 ? Why not 1 Of what is the dust of dust-storms and blood-rains composed? Of what does the organic matter consist] 250 MISCELLANEOUS PHENOMENA. It may not be amiss to explain to the student in this place the meaning of the term infusoria. 624. INFUSORIA. The general name of Infusoria has been given to those minute living beings which can only be seen by the aid of the microscope. On account of their being first detected in vegetable infusions, they are termed infusoria ; and since they are exceedingly small, they have also received the appellation of animalcules, or little animals. They are found in countless myriads in all waters, and in the fluids that circulate in animal and vegetable bodies, while their shells and eggs are dissem- inated by the winds over every part of the world. 625. More than eight hundred distinct species have been discovered, possessing the most grotesque and sin- gular forms. Some resemble globes, trumpets, stars, boats, and coins; others assume the forms of eels and serpents, and many appear in the shape of fruits, neck- laces, pitchers, wheels, flasks, cups, funnels, and fans. Their minuteness is almost incredible, for the monad, the smallest of all living beings, never exceeds in length the twelve thousandth part of an inch. A single shot, one-tenth of an inch in diameter, occupies more space than seventeen hundred millions of these atoms each in itself a perfect being, amply endowed with vital powers adapted to the mode and range of its existence. 626. STRUCTURE. The outer covering of the infuso- ria is of two kinds ; i\iz first is soft and yielding, resem- bling the skin of the leech and slug ; but the second is a fine, transparent shell, possessing a flexibility like horn. Those animalcules that are protected by the latter integ- ument are termed loricated, from the Latin word lorica, a shell ; while the name illoricated, or shelless, is assigned to those which are invested with the softer covering. The material that composes the shells varies in different species. In many kinds it consists entirely of foint, and Describe the infusoria the number of their species their minute- MS. What is said re* pecting their structure 7 ness ITALIAN AND CALABRIAN DUST-SHOWERS. 251 in others of lime, united with oxide of iron. In some cases it is combustible. 627. When the loricated infusoria die, their shells re- main undecayed for ages, often congregated in such countless myriads as to form large portions of the earth's surface. The city of Richmond, in Virginia, is built upon an extensive bed of flinty marl, from twelve to twenty feet in thickness, filled with fowl, infusorial shells ; and it is stated by geologists, that nearly half of the bulk of all the chalk of Northern Europe is composed of the fossil remains of animalcules, and other minute shells. They are mingled with the mud that forms the bed of the Arctic Ocean ; they float with the iceberg in all its wanderings, and lie loosely scattered over the surface of every land. These hieroglyphics of nature are interpreted by the aid of the microscope.* 628. THE ITALIAN DUST-SHOWER OF 1803, AND THE CALABRIAN OF 1813. In the dust which fell in Italy during the month of March, 1803, forty-nine species of organic structures were discovered, and sixty-four in that which descended at Gerace, in Calabria, in 1813. Thirty- nine species in the Italian dust-shower, and fifty-one in the Calabrian, are identical with those discovered in more recent dust-storms. It is worthy of remark, that these two storms, though ten years apart, have no less than twenty- eight species in common, and in loth nearly all the species are of fresh-water origin. Among the numerous infusorial shells, four South American forms were discovered ; of these, one occurs in Peru, another in Surinam, and the remaining two belong to Chili. No animalcular structures were found exclusively African. 629. ATLANTIC AND CAPE DE VERD DUST. The dust "When the loricated infusoria die, what becomes of their shells 1 Of what did the dust consist which fell in the Italian and Calabriau dust-storms 1 * For further information on the subject of Living and Fossil Infusoria, see " Viewi of the Microscopic World," by the author; published by Fanner, Brace & Co., New York. 252 MISCELLANEOUS PHENOMENA. that was collected by Mr. Darwin on the Atlantic, in N. Lat. 17 43', W. Long. 26, and at the distance of about five hundred miles from the African coast, was submitted to the examination of Ehrenberg, who discovered that one- sixth part of it was composed of the flinty shells of fresh water and land infusoria, and of silicious fossil plants. There were eighteen species of the former, and as many of the latter. Of the animalcular remains, the greater part were European ; one species was decidedly of South American origin, and another probably ; but there were none that belonged exclusively to Africa. In the opinion of Ehrenberg, the two South American spe- cies were either brought from that country by the upper winds of the atmosphere, or from some other locality which is yet unknown. 630. In the dust of several other showers, which occur- red between the years 1834 and 1838, some at St. Jago, and some on the neighboring ocean, numerous organized structures were discovered, thirty of which were different from those detected in the dust just described. Among these were the shells of a few South American infusoria, and one beautiful microscopic shell, termed the Polytha- lamia* or many -chambered shell. A single species was observed that occurs in the Isle of France ; but none of the forms were recognized as peculiarly African. 631. Some of the dust collected by Mr. Ewbank, on his voyage to Rio Janeiro, was examined by Professor Bailey, of West Point ; but he was unable to discover in it any thing besides irregular, inorganic, mineral frag- ments. He believes, however, that more interesting results would have been obtained if the dust had been gathered with greater care. The entire number of distinct organic Relate, in full, what is said respecting the composition of the Atlan- tic and Cape de Verd dust. What is said respecting the dust of several other showers 1 .Were any of the forms distinctively African 1 ? Were any organisms discovered in the dust collected by Mr. Ew- bank ? What is, however, the opinion of Prof. Bailey 1 Vrom polity (Greek,) many, and thalamus, (Latin,) a chamber. SIROCCO DUST. 253 forms hitherto discovered in the Cape de Verd and Atlan- tic dust-storms is sixty -seven. 632. SIROCCO DUST. The dust that fell at Malta on the 15th of May, 1830, afforded forty-three distinct organ- ized forms ; of these there were fifteen infusorial struc- tures , twenty-one kinds of minute, petrified plants , and seven of Polytkalamia. The species of animalcules were, for the most part, identical with those discovered in the Cape de Verd and Atlantic dust-showers. MICROSCOPIC ORGANISMS OF THB LTOKS DUST-SHOWBR. (Fossil Infusoria.) One form was noticed belonging peculiarly to Chili, but none were found distinctively African. State the entire number of organic forms hitherto detected in th Cape de Verd and Atlantic dust-storms 254 MISCELLANEOUS PHENOMENA. 633. The Sirocco dust that fell at Lyons, on the 17th of October, 1846, was so rich in organic remains that they constituted one-eighth part of its mass. They consisted of numerous species of infusoria and of petrified plants, mingled with a few kinds of Polythalamia, and minute, vegetable fragments. The species were nearly all of fresh-water origin, one-seventh only being mwrine. In figures 45 and 46 are delineated the various microscopic Fig. 46. Ul MICEO80OPIC OKGA.NI8M3 OF THE LYONS DU6T-SUOWER, (Fossil Plants.) organisms which were discovered in this dust. The most remarkable circumstance respecting it is the fact, that, notwithstanding its general resemblance to the dust of the Atlantic showers, which has always exhibited nothing but dead and empty infusorial shells, this, on the con- trary, was found, in many cases, to contain a species of Describe the nature of the Sirocco dust that fell at Malta and at Lyons. 'What is remarkable respecting the Lyons showec ? ORGANISMS OF DUST- SHOWERS. 255 infusoria which was distinctly seen to be filled with green ovaries, or egg-sacks, and consequently was capable of Ufe. 634. The dust collected, in the preceding instances, from the Cape de Verd, Atlantic, and Sirocco showers, being nine in all, afforded 119 distinct organisms. Of these there were fifty-seven species of infusoria, and eight of Polythalamia forty- six kinds of fossil plants, together with particles of seven kinds of plants, and one fragment of an insect. Only seventeen of these organ- isms were marine / while 102, six-sevenths of the whole, consisted of fresh-water species. In all these showers the dust exhibited no indications whatever of volcanic origin. 635. In three dust-showers which occurred in the years 1847 and 1848 t\\z first in Salzburg, the second in Ara- bia, and the third in Silesia and Lower Austria similar fresh-water organisms were detected. The same South American species were here found, as in other showers, without any characteristic African forms. 636. The red snow that fell in the Tyrol on the 31st of March, 1847, afforded sixty-six different organic forms. Of these, twenty-two were infusorial structures, twenty- eig\\t fossil plants, two polythalamia, and thirteen par- ticles of plants. There was also one fragment of an insect. The greater part, by far, of all these species, were of land origin, two only being marine. A remarkable resemblance exists between the coloring matter of this shower and the dust of the Atlantic, Geno- ese, and Lyons storms, not only in its hue, but in its composition ; for out of these sixty-six structures, forty- How many distinct organisms were discovered in the dust of nine showers 1 Describe the several kinds. Was there any trace of volcanic dust in these showers 1 "What is observed respecting the dust-storms which happened in the years 1847 and 1848 \ What organisms were detected in the red snow of the Tyrolese etorni 1 What resemblance was observed between the coloring matter of this shower and the dust that fell on the Atlantic, at Genoa, aiid at Lyons 1 256 MISCELLANEOUS PHENOMENA. six are found in the Atlantic and Sirocco dust ; and twelve species of infusoria and twenty of fossil plants are com- mon to all. 637. In the dust that fell, mingled with snow, at Olsterholz, in the year 1850, Ehrenberg detected fifty organic forms, forty of which he had previously observed in the dust of other showers. The remaining ten species had never been before discovered in atmospheric dust, 638. NUMBER OF DISTINCT ORGANISMS DISCOVERED. In the dust of the various showers examined by this dis- tinguished naturalist, no less than 320 distinct species of organisms were discovered. Of these, five only were of marine origin, and fourteen were forms peculur to America. 639. NUMBER AND EXTENT OF DUST-STORMS AND BLOOD-RAINS. According to the researches of Ehren- berg, 340 instances of dust-storms and blood-rains are mentioned in history and in the annals of science, of which 81 took place before the Christian era, and 259 after it. These remarkable phenomena extend through- out the world, occurring on the ocean, on all the conti- nents, and even in Australia. They appear, however, to prevail most within a zone, extending from that part of the Atlantic off the west coast of Middle and North Africa, along in the direction of the Mediterranean Sea, reaching a short distance north of this sea, and continuing into Asia between the Caspian Sea and the Persian Gulf, perhaps to Turkistan, Kaschgar, and even China: they seldom happen as far north as Sweden and Russia. This zone, according to the observations of Captain Tuckey, has a breadth of 1800 miles. "What organic forms were discovered in the dust that fell at Olster- holz 1 How many distinct organisms have been detected by Ehrenberg in the dust of numerous dust-storms 1 What is said respecting their origin 1 What is the number and extent of dust-storms and blood-rains, accord- ing to Ehrenberg? Where do they appear to prevail most ? What is the breadth of this zone 1 ORIGIN OF THE DUST. 257 640. THEIR PERIODICITY. These phenomena occur most frequently during the first half of the year ; for out of 199 showers, whose dates are ascertained, 118 happened between January and July, and 81 between July and December. The distribution of the shovfers through the several months is as follows : January, 27. July, 9. February, 14. August, 17. March, 23. September, 7. April, 18. October, 18. May, 18. November, 16. June, 18. December, 14. 641. ORIGIN OF THE DUST. The color and nature of this dust ; the circumstance that a great quantity of earthy matter sometimes falls in a single shower ', as in that of Lyons ; and the fact that dust-storms and blood- rains have occasionally happened from the time of Homer (900 B.C.) to the present day, have led Ehrenberg to advance a most extraordinary hypothesis. He believes that these phenomena are not to be traced to mineral mat- ter belonging to the earth's surface ; neither to masses of dust revolving in space, like the meteoric matter of Chaldni (Art. 555) ; nor yet to the influence of atmospheric cur - rents, such as the trade-winds and harmattan, carrying the dust of the earth aloft into the air ; but to some gen- eral law, as yet unknown, according to which infusoria, and other living organisms, exist and are propagated in the upper regions of the atmosphere. The locality which constitutes the dwelling-place of these organisms he imagines to be of vast extent, and to be sit- uated at the height of about 14,000 feet above the sea- level. In what parts of the year do these phenomena most frequent.y occur 1 How are they distributed through the months 1 What are the views of Ehrenberg respecting the origin of the dust that falls in these singular storms 1 Where does he suppose the abode of these organisms to be sit- uated 1 258 MISCELLANEOUS PHENOMENA. 642. The apparent periodicity of the showers he ac- eounts for by supposing that this cloud of organisms lies in the region of the trade-winds, and suffers partial and pe- riodical deviations. 643. In the present imperfect state of our knowledge in regard to these phenomena, it would be highly unsafe to adopt this singular hypothesis. Both the organic and inorganic matter contained in these storms are terrestrial in their nature, and the at- mospheric currents are most probably the agents, which elevate this dust from the surface of the globe, and bear it along to distant regions. 644. The opinion, that the Atlantic, Cape de Verd, and Sirocco dust comes from the deserts of Africa, is incon- sistent with certain known facts respecting it, and has therefore not been universally adopted. For instance, the color of this dust is red, while the sand of the African Saharas is white and gray j and we have also seen that none of the organized forms which it contains are peculiar to Africa ; while many of them are distinctively South American. 645. It is the belief of Lieutenant Maury, that the red powder, which falls in these dust-storms, is brought by an upper wind from South America to Africa ; where it de- scends and becomes the lower trade-wind, which dissem- inates the dust throughout the regions where it blows. It is not improbable that a portion of this dust, carried on- wards by the higher current, falls within the sweep of the Sirocco a circumstance which will fully explain the sim- ilarity that exists between the Sirocco and Atlantic dust. How does he account for the apparent periodicity of these showers and storms 1 Are there, at present, sufficient reasons for adopting this hypothesis ? What is the nature, both of the organic and inorganic bodies, which constitute this dust 1 ? How are they probably raised into the atmosphere 1 What reasons exist for believing that the Atlantic, Cape de Verd, and Sirocco dust does not come from Africa 1 What is the opinion of Lieutenant Maury upon this point 1 How can the similarity in the nature of the Sirocco and Atlantic dust be explained ] VOLCANIC SHOWERS. 259 VOLCANIC SHOWERS. 646. The fall of ashes and dust soon after the eruption of volcanoes, is a phenomenon entirely different from dust-storms and blood-rains y for the materials which are precipitated in volcanic showers contain no organic forms ^ and are easily traced to their source. 647. CAUSE. The mighty energies that are at work, when a volcano is in full action, carry up the lighter por- tion of the ejected matter high into the air; it is then borne along by the upper winds, and at length falls, in showers, in regions often far remote from the burning crater. 648. INSTANCES JORULLO. During the eruption of Jorullo, in Mexico, which began on the 28th of Septem- ber, 1759, the sky was darkened with clouds of dust that afterwards fell at Queretaro, 100 miles distant ; and during another eruption of the same volcano in 1819, dust, to the depth of six inches, descended in the streets of Guanaxuato, at the distance of 160 miles. 649. SOUFFRIERE. One of the most remarkable vol- canic dust-showers on record is that connected with the eruption of the Souffriere mountain, in the island of St. Vincent, which occurred on the 30th of April, 1812. 650. On the 27th of this month the volcano, which had been slumbering for a hundred years, again burst forth, showering down sand, mixed with ashes and gritty, cal- cined particles of earth. This dust, driven before the wind, darkened the air like a cataract of rain, and covered the ridges, woods, and cane-lands with light grey-colored ashes, resembling snow. As the activity of the volcano increased, this continual shower extended farther and farther, destroying every trace of vegetation. 651. For three days the appearance of the burning mountain grew more awful and portentous, when at length, on the night of the 30th, a most terrific eruption State what is said respecting volcanic showers their cause. Give an account of the showers attending the eruptions of Jorulio. What remarkable ghower of this kind is next mentioned 1 D scribe it. 260 MISCELLANEOUS PHENOMENA. took place. From the midst of a lofty pyramid of flame issued streams of glowing lava, which, pouring down the sides of the mountain, flowed in torrents to the sea ; while the sullen roar of these burning rivers was swelled by the thunderings and loud explosions of the crater. Stones, fire, ashes, and calcined masses rained down for hours, and earthquake following earthquake, almost incessantly, the whole island undulated like water shaken in a bowl. 652. On the next day, the air was so filled with vol- canic dust, that it was dark at 8 o'clock in the morn- ing ; a dense haze shrouding sea and land. Most of the plantations in the vicinity of the Souffriere mountain were covered ten or twelve inches deep with dust and stones. 653. But the effects of this eruption were not confined to this island. During the night of the 30th the terrific explosions of the volcano were heard as far as Barbadoes, which is situated seventy miles due east from St. Vin- cent. On the next morning, at 4 o'clock, the atmosphere at Barbadoes was bright and clea/r. but at 6 o'clock the sky was obscured by thick clouds, from which issued in torrents, like rain, particles of volcanic matter finer than sand. At 8 o'clock, an appalling darkness, as intense as that which prevails in the depth of a stormy night, over- spread the island, and continued till noon, but the showers of dust still descended at intervals until 7 o'clock in the evening. 654. This dust descended to the depth of two inches, and, according to the computation of observers, an average weight of 40,000 Ibs. rested upon every acre on which it fell. Vessels at sea, some 300 miles, and others 500 to the windward of St. Vincent, had their decks covered with this volcanic dust. (Art. 103.) 655. TOMBORO. Still more surprising was the dust- shower, caused by an eruption of Tomboro, a volcano sit- To what other island did this dust extend 1 How far is it from St. Vincent ? How was the atmosphere of Barbadoes affected by this volcanic dust? At what distance from St Vincent were vosaels covered with thii dust ! ERUPTION OF COSIGUINA. 261 uated in the island of Sumbawa, which lies east of Java, and south of Borneo. 656. The eruption occurred on the 12th of April, 1815. According to Sir Stamford Raffles, who was then governor of Java, the roar of the volcano was distinctly heard, in one direction, at Ternate, 720 miles distant from Tomboro, and in another, as far as Sumatra, at the distance of 970 miles. 657. Such vast clouds of ashes and dust were ejected, that the day at Sumbawa was as dark as the blackest night ; these, rising within the sweep of the higher winds, were carried in immense quantities to Java, 300 miles distant, and hung like a pall over the island. At Macas- sar, 250 miles from Sumbawa, a total darkness prevailed long after the sun had risen, and volcanic dust fell an inch and a half deep. Some of the ashes were carried even as far as the island of Amboyna, which is situated 800 miles from Tomboro. 658. Near Sumbawa, such quantities of lava, cinders, and ashes fell into the sea, that they formed a cake on the surface two feet in thickness, and, for miles around the island, the ocean was so completely covered with this floating matter, that the progress of ships was materially impeded. 659. COSIGUINA. During the eruption of the volcano of Cosiguina, in Nicaragua, on the 20th of January, 1835, immense clouds of dust darkened the sky, and were borne by the winds to a great distance. 660. At Union, a sea-port on the western shore of the bay of Conchagua, and the nearest place to the volcano of any importance, showers of dust fell at intervals from the 20th to the 27th of January. It descended in the form of a fine powder like flour, and in such quantities as Describe the eruption of Tomboro. What is said respecting the ejected ashes and dust 1 How did they affect the atmosphere, and how far were they car- ried 1 What is said of the condition of the sea around Sumbawa 1 Give an account of the showers of ashes and dust caused by th eruption of the volcano of Cosiguina. 262 MISCELLANEOUS PHENOMENA. to cover the earth to the depth of five inches ; causing, for the space of forty-three hours, so intense a darkness that lights and torches were needed, and even these were insufficient to render objects clearly visible. 661. At Leon, the capital of Nicaragua, showers of ashes and dust descended on the 23d of January to the depth of nine inches / and at Nacaome the falling dust was mingled with coarse sand, which, together, formed a layer upon the surface of the ground seven or eight inches deep. Some of the ashes ejected during this eruption were carried even as far as Kingston, Jamaica, seven hundred and thirty miles distant from Cosiguina. (Art. 103.) 662. YELLOW RAINS POLLEN-RAINS. Showers of rain, mingled with recent vegetable matter, consisting of the pollen of various plants, have been noticed for a con- siderable period of time. A shower of this kind once fell at Lund, in the south of Sweden, the pollen having been borne by the wind, from a forest of fir, thirty-five miles distant. A similar rain fell on the lake of Zurich, in the year 1677, and another of the same nature, at Bordeaux, in 1761. During a thunder-storm at Banff, in Scotland, on the 9th of June, 1835, a shower of yellow rain de- scended, which tinged the waters of the river Devern and of the neighboring pools with the same color. The hue in this case, as in the preceding instances, was derived from the pollen that was mingled with the rain. 663. A few years ago, a rain of this color extended over the western and south-western regions of the United States. At Carrollton, Ohio, the ground, after the rain, was covered with a yellow substance and the same phe- nomenon was likewise noticed at this time at Zanesville, Cincinnati, Louisville, St. Louis, Natchez, and New Or- leans. The hue of this rain is undoubtedly to be attrib- uted to the presence of pollen. 664. GOSSAMER-SHOWER. A phenomenon of a very extraordinary nature was observed by the Rev. Gilbert "What is a pollen-rain 1 Give the several instances. GOSSAMER-SHOWER. 2C3 'Vhite, on the 21st of September, 1741, and of which an account is given in his charming " Natural History of Selborne.' 5 It appears from the statement of this gentle- man, that on the day just mentioned, at about 9 o'clock in the morning, a shower of cobwebs , falling from very ele- vated regions, was observed, and which continued to descend, without any interruption, till the close of the day. 665. These webs were not single, filmy threads, but perfect flakes or rags some being nearly an inch broad and five or six long, which fell with a degree of velocity that showed they were considerably heavier than the at- mosphere. On every side, as the observer turned his eyes, he might behold a continual succession of fresh flakes falling into view, and twinkling like stars as they reflected the rays of the sun. This singular shower was noticed at Bradley, Selborne, and Alresford, three places which lie in a kind of triangle, the shortest of whose sides is about eight miles long. Whether it extended farther, is not certainly known. ' 666. At Selborne, a gentleman, who observed this phe- nomenon while taking his morning ride, supposed, at first, the falling flakes to have been blown, like thistle-down, from the fields above, and imagined that he would be free from the shower when he had gained the summit of a hill that rose near his house. But upon reaching this point, 300 feet higher than his residence, he found the webs, in appearance, still as much above as before still descending into sight in a constant succession, and twinkling brightly in the sun. Neither before nor after was any such fall observed in these places, but on this day the gossamer flakes hung so thickly in the trees and hedges, that a person might havo gathered them by ~baslcetfuls. 667. In explanation of this curious phenomenon, Mr, Give an account of the gossamer-shower described by Rev Gilbert White. Ho\v does he explain this phenomenon 1 2G4 MISCELLANEOUS PHENOMENA. White observes, that the gossamer threads, which fk&t in the air, are the production of small spiders, that swarm in the fields in fine weather in autumn, and have the power of shooting out webs so as to render themselves buoyant and lighter than the air. If taken in the hand, they will run along the fingers, throw out a web, and sail aloft. He supposes, that, possibly, these spiders, with their webs, are carried up into the higher regions of the atmosphere by the warm and light currents of air which ascend from the earth ; and that while thus elevated they have the power, perhaps, of thickening their webs as some naturalists sup- pose thus rendering them heavier than the atmosphere, when of course they must fall, and will thereby occasion, if they descend simultaneously in large flakes and in great abundance, a gossamer-sJwwer. 668. Dr. Lister ascended one day, when the air was very full of gossamer, to the highest part of York Minster, and still found these filmy threads floating far above him. CHAPTER II. DRY FOG AND INDIAN-SUMMER HAZE. 669. DRY FOG. A peculiar haze sometimes pervades the atmosphere, which has received from meteorologists the name of dry fog. It is different from humid mist, for it not unfrequently prevails when no visible vapor exists in the air, and during seasons of great heat. 670. When this phenomenon occurs, the sky, although it may be perfectly free from clouds, has lost its fine azure tint, and is dull and discolored. Terrestrial ob- jects at a distance, and of a deep color, are lost to view, and appear as if covered with a blue veil. The sun loses "What did Dr. Lister observe 1 What is dry fog 1 How does this phenomena affect the appearance of celestial terrestrial objects ? DRY FOGS. 265 its brilliancy, even when high in the heavens, and its light is of a reddish hue. As it approaches the horizon it as- sumes a blood-red color, and may be gazed at without dazzling the eyes. At times, the haze is even so thick that the solar orb ceases to be visible before it has descended below the horizon. 671. INSTANCES. In the year 1782, a remarkable fog of this kind occurred, extending over Europe from Lapland to the Mediterranean. It was succeeded the next year by another still more extraordinary. This fog, known as the dry fog of 1783, produced a great sensation throughout Europe. According to Kaemtz, its intensity was such, that in some places objects at the distance of three miles could not be distinguished. Sometimes they appeared blue, or else surrounded with vapor. The sun, shorn of its beams, appeared of a fiery red, and at noon could be looked at without injury to the naked eye. At its rising and setting it was completely obscured by the dense haze. This dry fog first appeared at Copenhagen on the 26th of May. It reached Rochelle on the 6th of June, and was noticed, almost everywhere throughout Germany, France, and Italy, from the 16th to the 18th of this month. It was seen at Spydberg, in Norway, on the 22d of June, at Stockholm two days after, and on the 25th it appeared at Moscow. In Syria it was observed towards the close of June, and on the 1st of July it shrouded the Altai mountains. In England it continued from the 23d of June until the 20th of July. During the prevalence of this phenomenon the heat was intense. 672. In the sinnmer of the year 1834, dry fogs were noticed in various localities in Germany. Kaemtz ob- served one on the 29th of May, enveloping one of the peaks of the Hartz mountains. Give the instances stated. 12 2G6 MISCELLANEOUS PHENOMENA. For three days, during the latter part of this month, & haze of this kind prevailed at Munster, and the phenom- enon was seen at Halle, Freiberg, and Alteuberg, in Sax- ony, on the 28th and 29th of July. In the northern and western parts of Germany, as well as in Holland, dry fogs very frequently occur. 673. CAUSE. The origin of this phenomenon is not yet satisfactorily explained. Many philosophers suppose it to arise, either partially or wholly, from the influence of elec - tricity, without being able to show very clearly in what manner it is possible for this agent to produce such an effect. Others believe it to result from smoke caused by the conflagration of forests, the burning of peat-bogs, and the eruption of volcanoes. Thus Lalande attributed the dry fog of 1783 to electricity, Cotte to the union of metallic emanations with electricity, while other philos- ophers traced it to a volcanic source. 674. In the opinion of Kaemtz, the dense, dry fog of 1834 arose, partly from the combustion of peat, and partly from the unusual number of extensive fires that occurred in this year. While the fog was among the Hartz mount- ains and in the vicinity of Orleans and Basle, many peat- bogs were reduced to ashes, the fire penetrating deeply beneath the surface. One bog in particular, that of Dachau, in Bavaria, was burned to the depth of more than eight feet, the fire running even beneath ditches filled with water. In July there were vast conflagra- tions of forests and peat-bogs in Prussia, Silesia, Sweden, and Russia. The drought, which then prevailed, favored the propagation of these fires and the diffusion of the smoke. 675. The dry fogs, that occur in Holland, and in the north and west of Germany, are attributed by Finki to the combustion of peat. 676. INDIAN-SUMMER HAZE. Throughout the conti- What is the cause of dry fogs 1 What views are held respecting them 1 HOY? is the dry fog of 1834 accounted for by Kaemtz 1 What is Finki's opinion regarding the origin of the dry fogi ol Holland and Germany 1 INDIAN-SUMMER HAZE. 267 nent of North America, there occurs, about the close of October or the beginning of November, a warm and pleasant interval, termed the Indian summer, which lasts for the space of two or three weeks, and agreeably retards the approach of winter. During this season the air is soft and bland, and a mild temperature prevails, while the atmosphere is filled with a dense, dry haze, that causes the distant objects of the landscape to appear as if veiled in a cloud of smoke. 6TT. CAUSE. This obscurity has been supposed by some writers to originate in the same way as aqueous mists j while others imagine it to be due to the presence of smoke, borne by the wind from the distant conflagra- tions of vast prairies and forests. In respect to the first view it may be remarked, that the Indian-summer haze bears little resemblance to an aqueous mist. It does not change into rain, and during its continuance the hygro- metric state of the atmosphere is different from that which exists when moist fogs occur. The second hypoth- esis fails, inasmuch as it assigns a local cause for the solution of a general phenomenon not to mention other objections which might justly be urged against it. 678. No sufficient explanation of this singular phenom- enon has yet been found, but there is one circumstance connected with it which may possibly give a clue to its cause. The Indian summer, with its genial warmth and misty veil, occurs at that period of the year when the leaves of the forest are falling, and the vegetation that covers the surface of the earth is beginning to decay. In view of this fact, the author was led to think, some years ago, that the decomposition of the decaying vegetation, which Liebig What is the Indian summer 1 ; What opinions are entertained in regard to its haze ? Has any adequate explanation been yet given ? What circumstance is worthy of notice in connection w'th this phe- nomenon 1 In view of this fact, what has been supposed ! 268 MISCELLANEOUS PHENOB1ENA. terms a slow combustion, (eremacausis), might impart that peculiar haziness to the atmosphere which is seen during the Indian summer. It was afterwards ascertained that this phenomenon was ascribed to the same cause by another ob- server, Dr. E. B. Haskens, of Clarksville, Tenn,, who also "suggests," that the Indian-summer haze consists of carbon- aceous matter or smoke produced by the oxidation of the lifeless vegetation. The warmth of this season he attributes to the same cause. These views, however, are merely spec- ulative. SHELDON & COMPANY'S &cjjaol antJ d/flllejjiaU JO would call the Especial attention of Teachers, and of all who are interested in t?te subject of Education, to the following valuable list of School Books: BULLIONS' SEEIES OF GEAMMAES, Etc, A Common School Grammar. Being an Introduction to the Analytical and Practical English Grammar, { This work for beginners has the same Rules, Defini- tions, etc., as the Analytical and Practical English Grammar. A complete work for Academies and higher classes in Schools, containing a complete and concise system of Analysis, etc., Progressive Exercises in Analysis and Parsing. Latin Lessons, witJi Exercises in Parsing. . . 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