Our Planet and its Relation to the Universe
( Originally Published Early 1900's )[an error occurred while processing this directive]
WHETHER man was given a beginning in a Mesopotamian Eden, or awoke to intelligence in some cradling valley of Central Asia, his first impression of external things no doubt concerned itself with conjectures regarding the sun, moon, and stars.
In this age we take, as a matter of course, the endless procession of days and nights, the seasons, the various stages of the moon, and too seldom indeed is our gaze directed towards the starry heavens. A little reflection on these things will prove wonderfully refreshing to the mind ordinarily intent upon business cares, and no other study costs so little or repays the student so well.
In the annals of every race, no matter how primitive it may be, are found references to the heavenly bodies. Religions of the past wrote the stories of their gods and goddesses into the star groups, or constellations, and the names these groups bear have immortalized deities and heroes who were as real to the people of the past as Washington, Franklin, Lincoln, and Lee are to us of the present day.
The earth we dwell upon is a body of spherical shape and swings about the sun, describing not quite a true circle in its path, or orbit. The earth is about 8,000 miles in diameter, and, owing to the fact that its path about the sun is not a true circle, its distance from that luminary will vary to some extent at different times of the year.
In the summer months we are about 92,450,000 miles away from the sun, and in the winter we are about 3,000,000 miles closer. At first glance it would seem that our winter months should be warmer on this account, and the reason they are not, so far as the Northern Hemisphere is concerned, is interesting.
Imagine, if you can, a line drawn from the center of the sun to the center of the earth. Instead of entering the surface of the earth at the Equator—that imaginary circle which divides the earth into two hemispheres, North and South—this line from the sun will enter the earth at a point 23½ degrees north or south of the Equator, depending upon the location of the earth in its orbit, though it will coincide with the Equator for a few days twice a year, at the time of the Equinoxes—that is, at those times when the nights and the days are of equal length.
This indicates that the earth must be "tipped," or is leaning either away or towards the sun, so far as the North Pole is concerned, else the line would always enter the earth's surface at the Equator. And this is a fact. It happens that when the earth, as a whole, is nearest the sun, in the month of January, the North Pole of the earth is leaning away from the sun, and the waves of radiant energy sent out by the sun do not fall direct upon the Northern Hemisphere, but on an angle, or "slant," and as a glancing blow is never as efficacious as one that is delivered direct, these waves do not have the same heating effect. And furthermore, the sun being so far to the south makes the days short and the nights long, and the little heat that is received cannot be "stored up" as it is through the long days and short nights of the summer season.
In the Southern Hemisphere, at this same time of the year, the South Pole of the earth is presented to the sun, and the southern continents of South America, Africa, and Australia have their summer season, with long days and short nights. Six months later, when the earth is at its farthest distance from the sun, the North Pole of the earth is leaning towards the sun, and the waves of radiant energy fall directly upon the Northern Hemisphere, to give a summer season to those who dwell in North America, Europe, and the greater part of Asia.
From the foregoing it must not be considered that the polar axis of the earth changes its direction to make the earth lean away or towards the sun; it is that the sun is at a relatively fixed point, and the earth, in its orbit, always directs its polar axis to what we call the Pole Star, just as the reader might walk about a table lamp, carrying a cane which would be always pointed up and down at a certain angle towards the north and south, no matter in what direction he might be moving about the room.
The polar axis, it is true, does shift its general direction to some extent, but to a very small extent in comparison with the diameter of the orbit of the earth. The path of the earth about the sun might be considered in the same light as a weight attached to the end of a cord and swung rapidly with a circular motion. The cord which holds the earth in its orbit is that force called "gravitation," and it tends to draw the earth towards the sun just as the earth draws the article which you drop from your hands. Going back to the weight swung above your head by a restraining cord, the moment your hold upon the cord is released the weight shoots off through the air on a straight line, trailing the cord behind it. So with the sun and the earth. The force generated by the earth in its swing about the sun gives the earth a tendency to overcome the gravitational pull of the latter, and this keeps it from being drawn bodily into the fiery mass which constitutes the orb of day.
As the earth swings about the sun it always turns upon its axis once every twenty-four hours, with a speed at the Equator of 1,050 miles per hour. Thus it is that we have nights and days, depending on ,whether the place we live in is away from or towards the sun. When the people of New York are having their noon, it is midnight at that point which is exactly on the opposite side of the earth, for it is at that time away from the sun. And as the earth turns from west to east at the equatorial rate of 1,050 miles an hour, it will not be noon in Chicago till an hour later than in New York, and in Denver it will be two hours later, and in San Francisco three hours later. The hour of noon is determined at Washington, D. C., by certain calculations, and all points west of Washington will have their noon one, two, or three hours later, and points east of Washington will have their noon hour one hour earlier for each one thousand miles of distance. This applies to the United States.
In consequence of this difference in time for different parts of the United States, a person traveling from New York to San Francisco will find his New York time to be three hours fast in San Francisco, and if he were traveling in the opposite direction his San Francisco time would be three hours slow when he reached New York. And if he traveled the whole way around the world he would either lose or gain a whole day of twenty-four hours, depending upon his direction of travel.
If it would be possible to take a trip to the sun by rail-road train, traveling at the rate of 1,000 miles each day, we would be 254 1/3 years upon our journey, and would find an immense globe with A diameter of 866,500 miles, or about 109½ times that of the earth, and with a surface area of 12,000 times that of the earth. It is so hot that if this immense surface could be covered with a layer of ice 64 feet thick the ice would be melted in one minute's time. A still better idea of the intensity of the sun's heat may be obtained from the fact that such substances as carbon, and iron, copper, and other metals, subjected to it, are not only melted, but are in gaseous form. In other words, these substances have passed the molten condition and are in the same state as a drop of water becomes upon a red-hot stove, not alone changed to steam, but the steam in turn changed to gas. And in the sun's case this gas is heated to such a degree as to produce blinding light. It is really too hot to burn. All the combustible parts of it are gone, but it still exists in a state which is extremely hard to describe.
The surface of the sun is in a constant state of ebullition, or boiling, and great jets of this incandescent gas are thrown up to enormous heights, as much as 80,000 or 100,000 miles above the surface. At this height the gases become condensed to some extent, and in this state they prove themselves to be vapors of the various metals which exist upon the earth. Their nature is deter-mined by an instrument known as the "spectroscope," which came into use in the year 1860.
WHAT THE SPECTROSCOPE REVEALS
The spectroscope consists of a tube so arranged that an entering ray of light is carried through one or more prisms, or small, triangular pieces of glass. By these prisms the light rays are broken up into the colors of the rainbow, and by examining this rainbow effect by means of a magnifying lens the colors are seen to be crossed with dark lines. This array of colors is designated as a "spectrum."
When comparisons are made between the spectrum of the sun and that obtained by burning various metals, the same lines appear in certain colors of each. For example, certain lines are produced if iron is present in a flame, and as identical lines are found in certain colors of the solar, or sun's, spectrum, it is perfectly justifiable to believe that iron exists in the sun.
About forty of the elements found on earth are thus determined to be constituents of the sun, though in the form of fiery vapor. It is not unlikely that these vapors of the sun contain many other earthly elements in another foam, a form which would produce these elements under conditions of lower temperature. No one would recognize the principal constituent of a diamond in the black soot of a tallow candle, or in the lump of sugar dropped in the morning cup of coffee, and yet, under another condition of formation, the carbon of the soot or of the sugar would have been a diamond.
All the deductions of science point to the conclusion that the sun was at one time immeasurably larger than it is now, reaching out beyond the orbit of the farthest planet, Neptune. This planet is 2,800 million miles from the sun, and therefore the sun's diameter then must have been more than 5,600 million miles.
At that time, however, the sun was not as it is now. Instead of being a fiery mass its substance was a thou-sand times thinner than the air we breathe. But the substance was active; it was permeated with a force which the theologian calls the power of God, and which the man of science calls energy. As a leaven of yeast this force caused movement in this elemental substance, and the corpuscles thereof which were probably no more or less than electrical impulses—were drawn to and repelled from each other, in whorls and spirals, until they united to form a substance still thinner than air, but almost solid in comparison with its former state.
ORIGIN OF THE PLANETS
Millions upon millions of years passed, and the sub-stance grew more dense and drew in upon itself. The corpuscles vibrated in waves of certain length to produce light and heat, which in turn gave rise to other effects. Then came a time when the substance of the sun became almost as thick as water—it is but little more so now—and its speed of rotation, a natural effect of the whirling, swirling motion of its substance, became so great that immense drops of the fiery liquid were thrown off the parent body like water from a wagon-wheel.
These masses were rough and irregular in shape, but as they whirled in space, ever held by the long arm of gravitation to the parent sun, they took on spherical shape like clay upon the potter's whirling table, and they also commenced to cool. Before becoming solid, however, they in turn threw off masses of their substance which became "moons," and our moon was thus at one time a part of this world.
Just as a large substance will retain its heat longer than a smaller one, so our earth was a globe of fire for millions of years, and even now, though a thick crust has formed and hardened like slag from a furnace, and the waters of the rivers and oceans cover a large part of its surface—even now the interior of the earth is a fiery mass which bursts forth from time to time in volcanic eruptions.
The moon, however, with a diameter of one-fourth of that of the earth, became cold and lifeless long, long ago. But it is bound to the earth even as the earth is bound to the sun, and the force imparted to it on that day when it was flung 240,000 miles into space causes it to swing about the earth even as the earth swings about the sun. In the space between the suns of the heavens an object once set in motion will continue in motion until acted upon by another force. This is true on earth; it is true everywhere, but on the earth the gravitational effect of the earth will bring a moving object to rest in a very short time.
The moon's speed of rotation has slowed down, and for that reason it always presents the same face to us. As it circles about the earth in a cycle of twenty-eight days, at certain times it gets between the earth and the sun in such a manner that the sun's rays fall upon the side not visible to us.) As no light except reflected sunlight comes to us from the moon, we cannot see the moon at these times, and it is said to be "dark."
As it proceeds in its orbit it emerges from this position with relation to the sun, and a portion of the surface towards the earth is illuminated by the sunlight. It is then we see the crescent of the "new" moon. Later on the angle widens, and finally, when it is what might be termed "back" of the earth, and the sun shines full upon the surface presented to us, we have the "full" moon. Still later it gets into position between the earth and the sun so that the reflected light is diminished, and it passes into the "dark" stage again.
ECLIPSES OF THE SUN AND OF THE MOON
Sometimes the sun, moon, and earth get into such relation to each other that there is what is called an "eclipse." If the moon gets between the earth and the sun in proper position there is an eclipse of the sun. If the earth gets between the sun and the moon there is an eclipse of the moon. In either event it is merely a case of an obstruction in the sun's light, just as your hand might be placed before a lamp in a hallway and thus throw the lighted area into darkness.
The moon, in addition to giving light through the night, has an effect upon large bodies of water on the earth's surface, notably upon the oceans. Just as the sun pulls the earth, and the earth in turn pulls the moon, so the moon pulls upon that portion of the earth which is unstable. As a matter of fact, it draws upon all the earth, but the only appreciable effect of this influence is upon the oceans, wherein it causes "tides" by lifting up the waters. This lift, in itself, does not amount to a very great deal, but just as a snowball builds itself up by rolling over snow-covered ground, so the tides build them-selves up as they sweep towards the shores from far out at sea. At certain seasons of the year the sun and the moon pull together, and the result is a much higher tide than that caused by the moon acting alone.
OUR PLANETARY SYSTEM
We have referred to the earth as being a mass thrown off from the parent body of the sun, but it was not the only mass thrown-off. Between the earth and the sun are the orbits of two planets, Mercury and Venus, and beyond the earth are the orbits of Mars, Jupiter, Saturn, Uranus, and Neptune, in respective order of distance from the sun.
The name "planet" was given to these bodies by the Greeks, the word signifying "a wanderer," for it was noted by the ancients that these bodies were different from the stars, which seemed to be of permanent location. The ancients were right in this respect, for the planets are all members of the sun's family, and might be termed brothers and sisters of the earth, for they have the same parent, the sun, as a source of being.
AS TO LIFE ON THE PLANETS
There is much talk of the possibility of life on the planet Mars, due in great part to the peculiar markings on the surface when studied with a powerful telescope. There is also some telescopic evidence of atmospheric conditions being similar to those of this world, but science is far from being willing to state that life exists as we have life here.
The length of time required for a planet to complete its orbit or path about the sun is of course dependent upon its distance from the sun. We have seen that the earth takes one year, or rather a period of time which we call one "year." The speed of travel in the orbit is also another factor; in the case of the earth it amounts to eighteen miles per second in its journey about the sun.
From the table it will be noted that Uranus is over 82 years in making its journey, and far-off Neptune is almost 165 years on its ceaseless round. Uranus may be seen with the unaided eye as a very faint star, but Neptune requires at least an opera glass to be made visible. Both these planets have a greenish tint, so far as color is concerned. Mars is red, as is Saturn, and Jupiter,. Mercury, and Venus are bright in color.
Saturn is interesting on account of its "rings," which are whorls of gaseous matter surrounding the planet. Saturn has ten moons in addition to its rings. Jupiter has seven; Uranus has four; Mars, two; and the earth and Neptune, one moon each. One of Jupiter's moons is about 3,600 miles in diameter, and the others are about the size of ours. - Both of the moons of Mars are very small.
In the space between Mars and Jupiter there are several hundred bodies revolving about the sun, just as a planet might revolve, though they are widely scattered. Opinions differ as to their origin, though it is believed by some astronomers that they are the fragments of a disrupted planet which either exploded or was struck by a meteor, one of those wanderers from space which are called "shooting stars." None of them are very large, the majority-being masses of rock twenty or thirty miles in diameter. It has been computed that the total bulk of these "asteroids," as they are called, amounts to less than one-hundredth part of the bulk of the earth.
WHAT THE STARS REALLY ARE
So far we have confined our attention to our immediate neighbors in the heavens, and while the sun, moon, planets, and their satellites are of prime importance in our affairs, some of course to a less extent than others, the whole solar system is very insignificant in comparison with other objects in the heavens.
On, a clear night, when the moon is dark, the heavens glitter from zenith to horizon with thousands upon thousands of stars, and of them we will attempt to give a general description.
The people of ancient times had only the most remote idea of what the stars really are, though there are a few exceptions. Hipparchus, a Greek astronomer, who lived about 200 B. C., sensed the fact that what we call stars are suns like our sun, but so far away that they appear merely as points of light. It is also likely that the Egyptians had a very good conception of the stars. All manner of ingenious ideas were entertained by the majority of people to explain the evening skies' spangled draperies.
It was noticed at a very early date, probably in pre-historic times, that the sun seemed to travel in a regular path among the stars. As a matter of fact the sun does not travel among the stars to an extent that is appreciable except from the most complicated of observations. What actually happens is this : the earth in its orbit about the sun is, at different times of the year, between the sun and certain stars, if the word "between" may be used in this sense, and from month to month the stars of the evening sky seem to change, some dropping out of sight and others coming into view.
If the sun's light were blotted out for twenty-four hours, so there would be no daylight for that time, we would see all the stars of the heavens pass above us in a stately procession. As it is, we see certain stars this month, and as the stars do not keep time in their appearance with the setting of the sun, but gain four minutes each night, the stars we see this month pass into the west and a new group comes into our view. Those we see tonight are invisible to that half of the world wherein it is day, and when our part of the world comes again into the sun's light the stars are invisible to us, but visible in the night sky of the other half of the world.
For greater ease of expression it is customary to speak of the sun's "path among the stars," and for the sake of convenience we will refer to this path in speaking of the various star groups, or constellations. Pre-eminent among these groups are the "Signs of the Zodiac," a belt of constellations which marks the progress of the earth from month to month in its orbit about the sun.
THE SIGNS OF THE ZODIAC
The Zodiac may be considered as the numerals marking the hours on the dial of a timepiece, with the earth represented by the hour hand, and the sun by the pivot at the center of the dial. The center is fixed, but the hour hand moves from one numeral to another, and is thus between the sun and the "signs" as represented by the numerals.
There are twelve of these "signs" in the Zodiac, each covering 30 degrees of the 360 of the complete circle, and as the majority of them represent animals or animate creatures, the name of "Zodiac," or "Zone of Animals," was given to this belt by the ancients.
Though the majority of the names have descended to us from prehistoric times, they are still used by astronomers. They are considered, however, in a very different relation to the earth from the relation they once occupied. When astrology, the "parent of astronomy," was a flourishing "science," it was considered that people born at certain times of the year were gifted in some particular way, or were subject to this or that weakness, or tendencies to "certain organic troubles. Even today, in almanacs distributed by patent-medicine concerns, the signs of the Zodiac are seen encircling-the human body, with arrows pointing to various organs or parts which are liable to affliction as a result of these "influences." It may be that people born at certain times of the year, or during certain years, have a predisposition towards one thing or another, but most assuredly the stars have nothing to do with it. One could as well say that a railroad wreck was caused by a school-house because a school-house happened to be located near the scene of the wreck.
At a time when astronomy came to be studied in a more or less scientific manner—and this was many thou-sands of years ago—it was noticed that during the month marking the advent of Spring, or the Vernal Equinox, the sun always seemed to be in a certain constellation, and this constellation was given the name of Aries (the ram). A month later the sun seemed to be in another star-group, which was called Taurus (the bull), and so on through the entire twelve.
The names of these twelve constellations, and the symbols which have represented them from the most ancient times, are as follows:
Aries The Ram Libra The Balance Taurus The Bull Scorpio The Scorpion Gemini The Twins Sagittarius The Bowman Cancer The Crab Capricornus The Goat Leo The Lion a Aquarius The Waterman Virgo The Virgin Pisces The Fishes
No explanation has ever been given that is entirely satisfactory to explain the names employed for these star groups. A few may be explained as follows When the sun reaches the constellation known as Cancer, it starts "back" to the south, and this retrograde motion may have suggested the locomotion of a crab. In the same manner the sun, upon reaching the "sign" of Capricornus, commences to "climb" to the north, as a goat climbs a hill upon which it is grazing. Libra (the balance) may have marked the location of the sun when the days and nights are of equal length.
With very few exceptions the outlines of the constellations, as marked by the stars of each group, give no clue to the origin of the groups, but by aid of star maps or an atlas it is not difficult to locate the majority of them. Some of the groups are made up of a great number of bright stars, and others are outlined with such faint stars that it requires a great deal of patience to place them. As it is, the stars themselves are of greatest interest to the scientist, and the constellations only serve in a general way as an aid in finding them.
As with the constellations, the names of the stars have come down to us from ancient times, and, as previously noted, they bear the names of deities and heroes of the people of those times. It was a wonderful way to immortalize these names, preserved as they are in the firmament.
The reader will note, in the heading of the table, the term "light years" used as a unit to measure a star's distance from the earth. To give an idea of what this represents, the following analogy will be used: In watching a railroad train from the distance of a mile or more it will be noted that the steam from the whistle is seen several seconds before the sound of the whistle is heard. This is because it takes—at sea level—about one second for sound to travel 1,100 feet. If the train is a mile away the sound of the whistle will be about five seconds in reaching the ear. It also takes a certain length of time for light to travel from its source to the observer, though it travels at the almost incredible speed of 186,000 miles per second. Even at this speed the light from the sun is over eight minutes in reaching the earth.
A "light year" represents the distance that a ray of light will travel in one year's time, at the rate of 186,000 miles per second, and is numerically expressed as follows :
186,000 miles per second 11,160,00O miles per minute 669,600,000 miles per hour 16,070,400,000 miles per day 5,865,696,000,000 miles per year
The star nearest the earth, and which is too far to the south to be seen from the United States, is four and a half light years, or some twenty-six trillion miles away, and Sirius, the bright star of the constellation Canis Major, which may be seen in the southern sky in the evenings of February, is over eight light years distant. These stars are close at hand, in comparison with those for which no distance has been determined, and which are possibly as much #s 20,000 or 30,000 light years distant from the planet on which we live.
TThe reader must bear in mind that space is infinite. No matter how far away you may go from the earth, you may continue to go that much farther, and again that much farther. Space can have no limiting lines, for once a boundary is thought of the mind instinctively considers : What is beyond this boundary? So with eternity: one cannot imagine when time started, for that implies a preceding period which must be accounted for.
We have spoken of the possible origin of the sun from a very thin, gaseous elemental substance, and there is every reason to believe that all the stars originated in the same manner; for just as our sun is a star, though a small one, so all the stars are suns. As their substance is revealed by the spectroscope to be similar in nature to our sun, it is conceivable that they have a similar beginning. What the elemental substance may be we do not know, though science, as stated before, is inclined to believe it may be electric waves.
THE INVENTION OF THE TELESCOPE
While there has always been much ingenious speculation about the stars, practically nothing was known of them until after the invention of the telescope. There is a story to the effect that an optician in Holland made the first instrument, and it is known that a man named Lippershey applied for a patent upon such an instrument in 1608. Credit for the invention of the telescope is usually given to Galileo, who heard about the instrument made in Holland and developed one for himself in May, 1609.
Galileo's first telescope had a magnifying power of but three, but he soon improved upon this and made an instrument which magnified thirty times, and with it discovered the moons of Jupiter, and also identified the peculiar shadows on our moon as mountains. Glass-workers then became interested in the subject, and better lenses were made.
In. 1611 Kepler made substantial improvements in the instrument. The great trouble with the early telescopes was their size, which was necessary on account of the many imperfections of lenses, etc. A scientist named Huygens made an instrument 300 feet long, and in spite of this unwieldy length he arranged it so that very satisfactory results were obtained.
It was not until the nineteenth century that satisfactory object glasses and lenses were made, the great trouble 'being the production of flawless pieces of glass, which are necessary for this purpose. The first telescope was made on the plan of an opera glass, or spy glass, but with the development of the science and the discovery of certain laws of optics the "reflecting" type came into being, which is now the type most generally used.
In this form of instrument the observed object is reflected from a large concave mirror so arranged as to throw the reflected object upon a smaller mirror. This, in turn, directs the image to the eye through a magnifying lens.
The smallest star which it is possible to see with the unaided eye is what is known as a "sixth-magnitude" star. Vega, in the constellation Lyra, is of first magnitude; Polaris, the Pole Star, is of second; Megrez, marking the jointure of the handle and the bowl of the "Big Dipper," is of third; the three stars of Lyra nearest to Vega are of fourth; and the other visible stars in the heavens which are more faint are examples of fifth and sixth magnitude.
The magnitude of a star is not always a question of actual size, for the star may be so far away as to be almost imperceptible and yet be truly immense. This is not a hard and fast rule, for some of the first-magnitude stars are so far away that no idea can be obtained of their distance, even in light years. Such a case is that of Spica, the bright star in the zodiacal constellation Virgo (the virgin).
All the stars have a motion in space, some in the general direction' of the earth, and others in the opposite direction. The sun is traveling in the direction of Vega, carrying the earth and the other planets with him at a speed of about twelve and one-half miles per second. If a star seems to "shift" its location when observed from the opposite ends of the earth's orbit, and the apparent "shift" can be determined as a definite distance, it is possible to gain a general idea of the star's distance from the earth. Other methods are also used, and these, while extremely complicated, present no great difficulties to the mathematician if certain facts are known.
REVELATIONS OF THE LENS
The telescope has brought before us many wonderful objects, not the least of which are the "nebulæ," filmy, lacelike wisps of substance which can only be compared to fragments of a cloud, and yet in many cases they are so large that our entire solar system could be completely lost in their depths.
The Pleiades, or "Little Dipper," seems to be enmeshed in a nebula, and another nebula, visible on a dark night, may be observed in the sword handle of "Orion," just below the three stars which form the belt of the constellation.
The wonderful "Milky Way" is made up largely of nebulous clusters, which in a measure accounts for the pale luminescence marking its path across the heavens.
Not far to the east of Vega, and in the constellation Hercules, is what is known as a "star cluster," containing over six thousand suns, all enmeshed in a nebula. Each of these suns may be much larger than our sun, but the distance is so remote from us that only a high-power telescope can distinguish anything but a not overly brilliant single star.
Truly the heavens are full of wonders far exceeding anything upon this earth, though we in turn are a part of it all.
There are stars of almost every color, and of every age, from those new-born, like the brilliant star which came into the eastern heavens early in June of 1918, to those which are dead and dark and are only evident by the effect they have upon their companions.
Such dead stars wander through space, and sometimes collide with other stars. Then there is a tremendous explosion, and the heat developed burns the fragments of the two stars into gas, which may form a nebula which, in turn, may develop into a new star. With infinity as the scene of action and an eternity setting no limits of time, anything and everything may take place, and as a matter of fact this is precisely what does take place.
On a summer evening we often notice what we call "falling" or "shooting" stars. Thousands of them fall daily upon the surface of the earth and sea, but most of them are burnt up before they reach our planet. Their origin is unknown, but they may be fragments of exploded suns previously referred to, thrown so far into space as to come within the influence of the earth's gravitation. Traveling at an incredible rate of speed, the friction they encounter in passing through the earth's atmosphere causes them to be heated to an intense degree, and unless they are very large they are entirely consumed. Meteorites, as they are called, have been found in many places throughout the earth, and all show indications of being subjected to great heat. They are largely composed of iron.
Other visitors from space are comets. They are the strangest and least understood of all the phenomena of the solar system, of which they seem to be a part. Astronomers believe them to be groups of meteoric substances, together with various gases which have been ejected from some solar volcano, and thrown so far into space as to have an orbit of their own. The "head" of the comet has been called "a gravel bank," consisting as it does of masses of small stones or iron ore, though, instead of being packed together, the particles may be miles apart. With this material are probably various gases, which form the comet's "tail," and so thin is this gas that the amount in a "tail" of one hundred thousand miles in length "might be carried in a suitcase," as some one has expressed it. What makes it look so formidable is that each and every particle of this "tail" has the property of reflecting light, just as a cloud has this property, and, from the enormous distance that we are from these celestial visitants, we see the total sum of the reflections of each of these microscopic particles. If a comet should strike the atmosphere of the earth "head on," there would probably be an unusual display of "shooting stars," and that would be all there would be of it, but it would be the end of the comet itself.