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Les diagrammes suivants illustrent la m6thode. arrata to pelure, >n d n 32X 1 2 3 1 2 3 4 5 6 r »* 1 , ■. >-..« I l. t' eo^ra »v M.^jiMi€m&tm M r: %•.' ^'K0-tp*miim0mmm>^-^' micE '2<;'jmns ••—>**•»»■»•■' i il *--i A8TR0N0M1GALAND MATHEMATICAL GEOGRAPHY ■-;•■* BT M. PARKINSON PWNCff AL OrVEN3 STBEET aCHOOt,. TORONTO. Latb AjwmTANT MASTER, Strathroi Collrqiait: Inbtotjtk. ToBCHiTO : JTHE EDUCATIONAL PUBLIGHING CO. (JM2 n Entered accordinf to Act of the ParlUunent of Quuda In the rear one t'uiuaand eight hundred and ninety-nine, by The Educational PoBLMHiNO CoMPANT, at thc Department of Agriculture. "^ I PREFACE. HTHIS little maniial is a coAdensed statement of the chief facts in Astronomical and Mathematical Geography, •o far as they should be known to the pupils of our Public and High Schools. The teachers of Entrance and Leaving Classes in the Public Schools^ and of Form I. Classes in the High Schools will find, uroU|^nt within the compass of its one hundred pages, all the information rticessary to place these subjects intelligently before their pupils. At the same time tne book has been written in such a simple style that it is believed every pupil will easily understand each of its sections, and, with the volume in hand, readily prepare the work in this department of Geography for himself. The author puts forward no claim to originality. The collecting, classifying and simplifying of Astronomi- cal and Mathematical facts in relation to the subject of Geography has been his object ; and no excuse for pub- lishing such a work could be given if we had had in the market an inexpensive, comprehensive and trustworthy volume treating on such matters. The author would refer his readers to the followii|g •mti works for a fuller treatment of the subject ; and at the •ame time would acknowledge his own indebtedness to them : A New Astronomy.— American Book Company. Eci^KCTic Physicai, GsooRAPJaY.— American Book Company. Jackson's Astronomicai, GrographV.— D. C. Heath & Company. Stkelb's Drscriptivb Astronomy.— American Book Company. This Worij> of Ours.— Casaell 8l Company. The illustrations have been largely copied from the above works, but in every case acknowledgment has been made oi the jtacc. I£. PARKINSON. / PART I. THE HEAVENLY BODIES CHAPTER I. L^THE SOLAR SYSTEM. z. The Solar System consists of the following bodies :— I! Tke Sun-'-the centre. a. The Major Planets — Vulcan (?), Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus (ft'-ra-nQs), Neptune. 3. The Minor Planets^ or asteroids, at present (1899) five hundred in number. 4. The Satellites^ or moons, twenty-one in num- ber, which revolve around the different planets. 5. Meteors and shooting-stars. 6. Thirteen Comets^ which have now been found, by a second return, to move, like the planets, in elliptic paths, and to revisit the sun periodically. 7. The Zodiacal (zo-di'-a-cal) Light. , We are to imagine these bodies as suspended in space, held together by the law of gravitation, where- by each planet attracts every other' planet and is in turn attracted by all. ■,n»** THE H£AVENLY BODIES. In the midst is that great central globe—the sun. So vast is he that he can overcome the attraction of I The San and his Family. all the planets, and compel them to circle round him. Then come the planets, each turning on its axis while THE SUN. 7 it flies around the sun in an elliptical orbit. Then there are the satellites, or moops, each again rotating on its own axis, and at the same time revolving around its parent planet, while all whirl in a dizzy waltz around the great central orb. Last of all come the comets, rushing across the planetary orbits at irregular intervals of time and space; and the meteors and shooting-stars, u..rtl..g hither and thither, interleaving all in apparently inextricable confusion. The foregoing diagram will help to more th .oughly understand the Solar System. It shows all t!.e planets, their relative size, their distances froir he sun, an the sate^''^.^ » of each. II.-~THE SUN. I. The Sun's Distance—The average distance of the earth from the sun is 93,000,000 miles. But as the orbit of the earth is an ellipse, and the sun is situated in one of its foci, we are 3,000,000 miles nearer the earth in perihrlion (the point in the earth's orbit nearest the sun) t' ^n in aphelion (the point in the earth's orbit farthest from the sun). This distance is entirely beyond our grasp ; but we may get some conception of it if we consider the following : — (d) An express train travelling day and night at the rate of thirty miles per hour would require 352 years to reach the sun. If Shakespeare had started on this excursion on the day of his birth he would not yet be at the end of his journey. 8 THE HEAVENLY BODIES. {b) If a child were born with an arm long enough to reach the sun, and should touch that fiery globe, the infant would grow to man- hood, and finally reach old age and die, before the sensation could traverse the nerve to his brain and he feel the burn. 2. The Sun's Size. — The size of the sun is also entirely beyond our comprehension. To say that the sun is 865,350 miles in diameter gives us no concep- tion whatever of its size. The following illustrations may give a slight idea of its vastness : — {a) If wc should conceive for a moment the sun as a hollow sphere with the earth placed at its centre, and the moon revolving around the earth at its present distance, then the outer crust or rim of the sun would still be 190,000 miles from the moon. (J?) The hollow sun would require 1,300,000 worlds such as ours to fill its cavity. {c) The mass of the sun is 750 times that of all the planets along with their moons. (d) An athlete who could jump 6% feet from the ground on the earth would find that when transferred to the sun his highest jump could not exceed three inches. 3. The Sun's Light—The light of the sun is equal in brilliancy to the combined power of 5,563 wax-candles held at a distance of one foot from the eye. The amount of light received from the sun is equal to that from 600,000 full moons. 4. The Sun's Heat— The heat of the sun is again entirely beyond our comprehension. We may m ^ I THE SUN, 9 form some conception of the sun's heat from the amount of heat received by the earth from the sun. The heat faUing on five feet square of the earth's sur- face would produce sufficient energy to do the work of five men. If the heat falling on the deck of a steamer in the tropical ocean could be utilized, it would be sufficient to propel it at about ten knots an hour. But, when we, consider that the intensity of heat de- creases as the square of the distance from the radiating body increases, we find that the amount of heat radiated by a given area of the sun's surface must be about 46,000 times greater than that received by an equal area on the earth. The sun emits sufficient heat in one second to melt a solid cylinder of ice three miles in diameter, reaching from the earth to the sun. The question of " how the sun's heat is maintained " has occupied the minds of scientific men for centuries. Two theories have been advanced : — (i) Helmholtz, an eminent German physicist, pro- posed the theory that the sun's heat was produced by condensation of the sun itself, thus constantly chang- ing its potential energy into kinetic energy. So enormous is the volume of the sun that ai actual shortening of its diameter by six miles in a century would fully account for all the heat which it gives out. (2) Another theory accounts for the heat of the sun by assuming that there are vast numbers of meteors revolving round the sun and constantly rain- ing down on its surface. This theory would necessitate an amount of matter equal to a hundreth part of the earth falling from the present distance of the earth upon the sun during each year. to THE HEAVENLY BODIES. 5. The Physical Constitution of the Sun.— Very little is definitely known of the constitution of the sun. But it is fi;enerally supposed to be a \ast, fiery body, surrounded by an atmosphere of substances volatilized by the intense heat. The different por- tions of the sun are spoken of as follows : — (a) The nucleus, probably composed of gases, in the consistency of tar or pitch, on account of the intense heat and compression due to solar gravity. {d) The photosphere^ an envelope several thou- sand miles thick, which radiates the light of the sun. (c) The chromosphere ; this envelope, composed chiefly of hydrogen, surrounds the sun to a depth of from 5,000 to 10,000 miles. Tongues of fire from 100,000 to 350,000 miles in length shoot up through this chromosphere at the rate of 150 miles per second. ('S.^i..;.l'' 36 THE HEAVENLY BODIES. meteorological. The form of the crescent has no connection whatever with the weather. Neither do the phases of the moon have any effect on the curing of pork, making of soap, etc., as common people seem to believe. 7. Seasons. — The axis of the moon is nearly perpendicular to the plane of her orbit, therefore there can be no change of seasons. During nearly fifteen of our days, the sun pours down his rays upon the moon. No atmosphere intercepts this scorching heat. No clouds lend their grateful shade. This day is succeeded by a night of equal length, and of arctic cold, for the moon is not enveloped during this long period by a cushion of warm air, as is our world, and there is no atmosphere around the moon to prevent the great beat of the long day from radiating into space. 8. Telescopic Features.— The great modern telescope brings the moon within 150 miles, and as a result much detail of her inexpressibly lovely scenery can be made out. The surface of the moon is torn and shattered by fearful though now extinct volcmic action. The crust is pierced by craters, whose awful chasms and irregular edges testify to the great convulsions our satellite has undergone. One astronomer has counted 33,000 craters in the moon ; and, as the part of the moon turned from us may be supposed to contain features similar in kind to those on the hemisphere so ffimiliariy Irnown, there are probably at least 60,000 craters on the entire surface. These lunar volcanoes ^.rt? well shown in the accompanying photograph. I il, THE MOON. 37 Lunar VolcanoAs. Nearly 40 lunar peaks are higher than Mount Blanc. ""I'hc Leibint;i Mountains, perhaps the highest on the moon, are from 30,000 to 36,000 feet high, much higher than the highest peaks on earth. The crater of Copernicus is 50 miles in diameter, and the walls are 13,000 feet hi height. 9. If one were to visit the Moon.— < >f course no human being could live on the moon. Absence of air and water means absence of life, at least in the forms such as are known to us. But, if we could visit her, " how strange the lunar appeara^ice would be to us ! The disc of the sun seems sharp and distinct. The sky is black and overspread with stars even at mid-day. There is no twilight, for the sun bursts instantly into day, and after a fortnight's glare, as m ^iW*p:n'y 3» THE HEAVENLY BODIES. suddenly gives place to night ; no air to conduct sound ; no clouds ; no winds ; no rainbow ; no blue sky ; no gorgeous tinting of the heavens at sunrise and sunset; no delicate shading ; no soft blending of colors, but only sharp outlines of sun and shade. " The moon is a fossil world, an ancient cinder, a ruined habitation perpetuated only to admonish the earth of her own impending fate, and to teach her occupants that another home must be provided which frost and decay can never invade. The moon was once the seat of all the varied and intense activities that now characterize the surface of our earth. At one time its physical condition was like that of the parent earth, from which it had just separated ; but, being smaller, it cooled faster, and its geologic periods were correspondingly shorter. Its life age was perhaps reached while the earth was yet glowing." — Steele's Descriptive Astronomy. CHAPTER III. ECLIPSES OF THE SUN AND MOON. Solar Eclipses. — Lockyer beautifully says : " We may imagine the earth floating around the sun on a boundless ocean^ both sun and earth half immersed in it. This level, this plane, the plane of the ecliptic (because all eclipses occur in it), is used by astrono- mers as we use the sea-level. We say a mountain is so far above the level of the sea. The astronomer says the star is so high above the level of the ecliptic." THE MOON. 39 UlastratiiiK the Plane of the Bcliptie (after Jackson). In the above cut let the largest sphere represeot the sun, the smallest one the moon and the third the earth. Then the level surface of the water will represent this plane of the ecliptic. To an observer standing upon the ball representing the earth the other ball would stand in the surface of the water ; thus the plane of the earth's orbit is also the plane of the sun's apparent path, or ecliptic. Now if the orbit of the moon, as shown in the picture, lay in the plane of the ecliptic, it is clear that once each month the moon must come directly between the earth and the sun and an eclipse of the sun occur. That is, there would be an eclipse of the sun every new moon. Also, it will be readily seen, that tiiC oarth must, once each month, come directly between the moon and sun and an eclipse of the moon take place. That is, there would be an eclipse of the moon every full moon. Instead, how- ever, of the orbit of the moon lying in the plane of the ecliptic, it is inclined to that plane at an angle of about -f °. The points where the orbit of the moon cut the ecliptic are called nodts. Then an eclipse of 40 THE HEAVENLY BODIES. the sun can occur only when the moon is between the earth and the sun (new moon), and at or near a node. II How Eclipses of the Sua and Moon take place (after Todd). From the above figure it will be seen that the shadow of the moon cast upon the earth is in shape an inverted cone. This dark shadow is called the umbra. As the moon is smaller than the earth her cone of shadow is too small to cover the entire globe. The width of the space covered cannot exceed 1 80 miles, but, as the earth is constantly rotating on its axis during the duration of the eclipse, the shadow may travel over a large surface. People living in this region witness a total eclipse. Completely surrounding the umbra is a less dense shadow, from which the sun's light is only partly ex- cluded- Within this region there is a partial eclipse. 2. General facts regarding Solar Eclipses.— If we remember the following facts they may guide us in understanding the phenomenon of solai eclipses: THE MOON. 41 (i) An eclipse of the sun can occur only at new moon. That is, at conjunction, (2) The moon must be at or near a node. (3) An eclipse is not visible over the whole illuminated side of the earth. (4) The longest duration of an eclipse is about 12 minutes. (5) There cannot be more than five nor less than two solar eclipses each year, but very few of these are total eclipses. 3 Phenomena of a Solar Eclipse.— Durmg a total eclipse the darkness is so intense that the brighter stars and planets are seen, birds cease singing and fly to their nests, flowers close, a sudden chill falls on the earth, men take on a cadaveron*; ' ue and look at each other and behold, as it were, corpses. When the moon reaches just the point where she urst shuts off completely the light of the sun, the solar corona flashes out, and the total eclipse begins. Corona of 1878 (HarkocM). 42 THE HEAVENLY BODIES. 4. Lunar Eclipses. — An eclipse of the moon is caused by the earth coming directly between the sun and the moon. This can occur only at full moon — opposition. The moon must also be at or near a node. H I i I j Eclipse of the Mr^n (after Steele). This cut shows the position of the sun and moon during an eclipse of the moon. The space between the Unes Kr and \b^ on the opposite side of the moon from the sun, represents the umbra. Outside of this, where the sun's light is only partially cut off by the earth, is ^'O. penumbra. From a to ^ the moon is only partially eclipsed. From ^ to ^ she is totally eclipsed. From ^ to ^ the sun's light is again only partially shut off from the moon. ^«iiwiifiiiiiPiiroii»waW'^^ F»ARX II. THE EARTH CHAPTER IV. THE SHAPE OF THE EARTH. 1. The Rotundity of the Earth.— The earth is a great spherical ship, carrying you swiftly onward '1 ,: fC^-H^'v vS^ Earth and Moon in Space. in the ocean of space. We are to learn that the earth is a planet shining brightly in the heavens, and appearing to other worlds as a planet does to us. We 44 IHB EAKTH. are to learn that it is flying along its orbit with a speed incomparably greater than the swiftest express train ; that it is hanging in space held by the invisible power of gravitation. 2. What made the Earth Spherical ? -The same force that draws the particles of a raindrop together and makes it spherical ; the force that caused the molten metal dropped from a shot tower to form the tiny spheres of lead we call shot ; this universal force — f/ie aitradion of gravitation — caused the earth to assume the form of a sphere. When the matter which constitutes our earth sep- arated from the sun (see Nebular Hypothesis in our Physical Geography), this attraction, acting on the particles of matter, first drew two or three together, forming a small body, which attracted the neighboring particles more powerfully, thus causing them to gather round this body as a centre, and from the continua- tion of this process the earth was formed. Each particle, acting under the force of gravity, would endeavor to approach as near as possible to the centre, and thus form a sphere, just as a number of men, crowding around an object, form a circle. In ,this y we account for the spherical shape of the earth. 3. How we know the Earth is Spherical. — The original idea of the earth was that of an immense, flat, circular plane, around which Oceanus flowed like a vast river. The sky was a hollow hemisphere turned downward over it, thr ugh and across which the heavenly bf.:)dies coursed for human convenience and pleasure. We now know that the earth is round because : — \ I THE SHAPE OK THE EARTH. 45 {a) The curvature of the earth may be actually seen. As you stand on the shore^ and watch a vessel sailing away to sea, the hull of the vessel will appear to sink below the water, and the last to disappear will be the masts and sails. This is caused by the fact of the intervening " hill " of water. (If) Navigators have sailed around the earth. Final doubt of the shape of the earth was swept away when Magellan, in the i6th cen- tury, circumnavigated the globe. (c) The shadow of the earth on the moon during an eclipse of the moon is always circular. (See Eclipses, Chapter III.) (d) The horizon expands as we ascend an emi- nence. If we climb a hill we can see farther than we can from its foot. This is not because our eyesight is improved, but because the cur\'ature of the earth shut off the view of dis- tant objects when we stood at the foot of the 1-ill, and when we reached the top we could see farther over the side of the earth. The Horizon on a Round Earth. •N. 46 THE EARTH. I* \ i f ' ! ii N A person standing on top of the mountain will have the largest horizon. The person at the foot of the mountain will see least. ((?) The pole star seems higher in the heavens as we pass north. This would not be so except the earth were spherical ; if the earth were flat the pole star would be seen at the same height by all persons on the earth. (/) We may prove that the earth is spherical by the aid of the electric telegraph. If the earth were flat then the sun would rise on all parts of the earth at the same time ; if it is spherical the sun cannot rise at the same time on all parts of the earth, but must be rising at some place at all times. Now, if at lo a.m. at Chicago the telegraph operator asks New York the time, he will receive for answer it a.m.; if he asks Denver he will receive for answer 9 a.m. This difference in local time can only be explained by concluding that the earth is spherical. (g) All the other planets are spherical. Then, reasoning from analogy, our planet is spherical. This is the strongest of all the proofs, 4. The Earth is not a Perfect Sphere. (i) First, the earth is not a perfect sphere, becau.se its surface is uneven. Mountains, hills and valleys diversify the face of our earth. But, when we con- sider that the height of the loftiest mountain is no greater compared to the volume of the earth than is a grain of sand to the volume of a globe sixteen I THE SHAPE OF THE EARTH. 47 inches in diameter, we at once see that they merely roughen its surface to a very slight degree. (2) The earth is not a perfect i/zi^r^, because it is flattened at the poles. The true shape of the earth then is an oblate spheroid. The diameter of the earth from pole to pole is 7,900 miles ; in the plane of the equator it is 7,927 miles. Each pole is then depressed about 13^ miles, a little more than twice the height of a very higli mountain. 5. What made the Earth an Oblate Spher- oid? — This flattening gf the earth at the poles is caused by the earth's rotation. When the earth was in a molten condition (see Nebular Hypothesis) the particles at the equator would tend to fly off into space from the centrifugal force due to the rotation of the earth on its axis. This would cause the plastic earth to bulge out at the equator and sink in at the poles. In this way we account Jor the real shape of the earth. 6. How we know the Earth is not a Perfect Sphere. (a) By analogy we conclude the earth is flattened at the poles. All rotating bodies are subject to the law which flattens their poles. We know from observation that the other planets are flatter^ -f at their poles. Hence we reason that the eartL i ast also be flattened at its poles. # (b) A second proof is found in the difference in the weight of a body when weighed at the equator and again near the poles. The farther a body is canied above the surface of the earth the less it mm 48 THE EAKTH. weighs, and the nearer a body Is carried to the centre (granted it is above the surface) the more it weighs. Now, it is found that a body weighs more near the poles than it does near the equator. Thus we con- clude the poles are nearer the centre of the earth than is the equator. That is, the earth is flattened at the poles. A similar proof is found in the pendulum of a clock. A clock marking seconds at the equator will, if carried to, say, Winnipeg, gain time. While, if one marking seconds at Winnipeg be carried to the equator, it will lose time. The reason for this is found in the following: The attraction of gravity causes the pendulum to swing, and the nearer the centre of the earth it is the faster it will swing. The pendulum, smce it swings faster at Winnipeg than it does at the equator, must be nearer the centre of the earth at the former than at the latter place. (c) The earth is known to be flattened at the poles by actual measurement. The north star remains apparently motionless in the sky, excepting when we move towards or from it. If we approach the pole star over one degree of latitude, the star appears to rise one degree towards the zenith. By means of this it is possible to measure with great accuracy the length of a degree on any part of the earth's surface. Now, if the earth were a perfect sphere, the length of a degree would be the same no matter where meas- ured ; but such is not the case. A degree of latitude is 365,744 feet long in Sweden and 362,956 feet in India. This shows that, since the degree at the poles is longer than a degree at the equator, it must be a degree of a larger circle. That is, the earth must be flattened at the poles. I i THE SIZE OF THE EARTH. CHAPTER V. 49 THE SIZE OF THE EARTH. I. How to Measure the Earth.— We have already found out the shape of the earth ; now we come to the discus.sion of its size. We are to find out how far it is round the earth at the equator, how far from pole to pole. It is very plain that we cannot set out and measure it with a tape line. That would take too long and be too inaccurate. But we may measure A TtaeodoUto. a small portion of the way round, say a mile, with great accuracy, and from this, as a first step, arrive at the whole distance round the globe. In order that we may understand how this is done, it will be necessary to know something about the science of triangles. Yo'4 know that, if the length of the base of a triangle, and also the angles at the base, are given, the length of the sides and the 50 THE EARTH. I f ; I i remaining angle may be found. This is the fact on which all measurements that cannot be made by an actual tape are based. Suppose we wish to find the distance from the man at a to the church spire, as shown in the picture. We would first measure with great care a base from a to 6. Let this be loo yards in length. Then a b ^^^^^ ..4: ".7; .■»:.■ ^- if:'./-' .''■ :_"- ■^^^^'^ "*■"" ,:xiy:^:t^^^ '^ J Mouiureinent by Trlaogulatloo. is the base of our triangle. We now go to the end tf, and look at the church spire through an instrument called a theodolite^ and we find that the line a c along which we look makes, with the line a b, an angle of 87*8'. Now going to b, and repeating the observation, we find that the line b c makes an angle of 87" 8' with the line a b. '^v THE SIZE OF THE c^ARTH. 51 Now we have a triangle a b c, of which we know the length of the base a d, and the size of the two .angles at the base cab and c b a. Then from the science of geometry, we can readily find the length of a c and b c. For instance, we might cut a perfect model of the triangle a b c from a piece of cardboard, having the base one inch in length instead of 100 yards, and having the angles at the base exactly equal to the two angles we before measured, that is, 87° 8'. Then, carefully measuring the sides of our model, we would find them to be each 10 inches in length. Now, as the base of this model triangle is only j^^Vo" ^^ ^^^^ triangle a b c^ the side of the model is only ^-gVxr ^^ the si^e of the triangle a be. That is, a c\s 3600 x 10 inches, or 1,000 yards in length. Now, from our short base line of 100 yards, which we could measure with great accuracy, we have found with absolute accuracy a line a r, 1,000 yards in length, and the line a c may be now used as a base line to measure the distance to some point still farther away than the church spire. For instance, if we wish to find how far it is to the top of the distant mountain top in the picture, we proceed as before, using (I ^ as our base line. Then in the triangle ac d^ we know the length of the base a r, the angles cad and a c d. From this we find a dio be, 1 Jt us say, 10 miles. Then we may use a d?as a base to find the distance of still farther objects, and so on. And so it is possible to go on increasing the length of our measurements as long as we can see the object whose distance from us we want to measure. This is the way in which measurements of the earth's surface are taken. It is by this method of triangulation that the most accurate surveys of a country can be obtained. t9 .'-ipo* uXK ^'asss^faay^it.. 52 THE EARTH. 2. To find the Length of a Degree. Let us now see how what we have just learned of measuring long distances can help us in our problem, of finding the circumference of the earth. i I 1 / ""^ H ''jO _ nof s^oo® JJO. "^ la T oo" 00'* G\^ yb tw-^ y^"^ 1 Decrees in a Circle. Let the circle o o represent the circumference of the earth. Of course you will remember we have learned in Chapter IV. that the earth is not a perfect sphere, and therefore that its circumference cannot be a perfect circle. But fur our present purpose we will let this circle represent the outline of the earth. For convenience the circumference of every circle is divided into 360 equal parts called degrees. 1 here is no reason, other than convenience, why this number of divisions should be taken ; but you will notice that 360 has more factors tha 1 any other number you could choose, and it has been fixed on for that reason alone. Each degree is again divided into 60 minutes and each minute into 60 seconds. If in our figure N p is the north pole, s p the south THE SIZE OF THE EARTH. S3 pole and e e the equator, we shall readily see that from the equator to the noith pole will be 90 degrees. Now if we knew the length of one degree we could readily find the whole circumference of the earth by multiplying the length of one degree by 360. The question then is, Can we measure ike length of a degree ? and, if so, how ? Unfortunately for us there are no marks on the earth's surface to show us where one degree starts and another ends. But we have in the sky an object, the north star, from which we can always find how many degrees north of the equator we may be. The north or pole star may be easily found on any clear night from the following diagram. i.\ -J ■ 1 i I m ■ T 1 d 1 t ' 1 n > \ \ \ - •. ■ ■SI' V * , ■ ^ fl •- f\ ~ -- — — , The Pole k> — .— --■» 1 1 1 ; YhePole Star The (ireat Bear and the Pole Star. The Dipper or Great Bear is known to everyone, and is seen shining in the northern sky every night. The two outer stars of the Dipper point almost directly to the north polar star, as the above cut shows. ; ;^^gjy;ats THE MOTIONS OF THE EARTH. 59 A stone dropped from a cliff always falls a little fast of a vertical line. That is, it is thrown a little eastward bv the earth's rotation. If the earth'-:? rota- tion were rapid enough, the stone would fly off a^ong A Pendulum. ihe line a e. This would be so if the rotary motions should becomt swift enough to reduce the day to eighty-four minutes. But, as the rotation is not .nearly so rapid, the stone's departure from the vertical lin^ A c is comparatively slight. This distance c D 6o THE EARTH. |: ili- furnishes mathematicians with a means of determining the rate at which the earth rotates. (3) Suspend a ball of lead by a fme thread attached to the centre of a ruler. Hold the ruler in both hands, and set the ball swinging in the plane of the stick. Then, without raising or lowering it, quickly swing the ruler quarter way round its centre in a horizontal plane. The ball keeps swinging in the same plane as belbre, although it is n^)W swinging at right angles to the ruler. Now take a heavy leaden ball, fasten it to the roof, as in the picture, by a fme stoel wire, and set it swingmg, so that the fuie point in the ])enduluni end will make a slight scratch on the smooth fioor. The south end of the floor, being nearer the equacor than the north end, will trav< 1 eastward a little faster than the north end will ; and as the plane of oscilhition of the pendulum does not change, the marks caused by the sharp point will not all lie in the s:une place, but a more or less star-shaped figure will result. At the equator the pendulum marks only one line, l)ut the nearer the pole the nearer the ligure approaches the form of a star. 3. Solar and Sidereal Days. (i) A Sidereal day is the exact inten-al of time in which the earth rotates on its axis. It is found by marking two successive passages of a star across the meridian of any place. I'his is absolutely uniform, and occurs every 23 hours, 56 niiiiutes and 4 vseconds of mean solar time, (2) A Solar day is the interval between two suc- cessive passages of the sun across the meridian of any place. If the earth were stationary, the solar ' THE MOTIONS OF THE EARTH. 6i day would be of tlie same length as the sidereal day ; but, while the earth is turning on its axis, it is also going forward in its orbit. Thus, when the earth has made a complete rotation, it must perform a part of another rotation, in order to bring the same meridian vertically under the sun. These solar days are of unequal length. To obviate this difficulty astronomers have adopted a mean day, which is the average length of the solar days in the year. The clocks in common use are regulated to keep mean time. Thus the sun and our clocks do not always mark the same time. On the first of November the sun is sixteen and a quarter minutes too fast ; and on the tenth of "February it is fourteen and a half minutes too slow. This mean solar day is divided into 24 parts called hours. Thus 24 hours of mean solar time are equal to 23 hours, 3 minutes, 56 seconds of sidereal time. From what has been said, it follows that the earth makes 366 rotations in 365 solar days. 4. The Effects of the Earth's Rotation^ (a) The determination of an axis^ poles and Equator, The earth rotates upon its shortest diameter, called its axis. The ends of the axis are called poles, A line drawn around the earth, mid-way between the poles, is called the equator. {b) The flaitening of the poles. See Chapter IV., Section 5. {c) The apparent rotation of the heavens in the opposite direction. ^ 62 THE EARTH. By observing the heavens it Vill bo seen that the north star 'remains stationary, while the stars near the pole star seem to move in small circles around it every twenty-tour hours. Stars farther off describe larger circles, while those over the equator desciibe the largest of all. {d) Alternation of day and night. The sun shines upon one-half of the earth at a time. The other half being turned away from the sun is in darkness. As the earth rotates, each point on its surface is carried necessarily into the light and into the darkness, one day • and one night marking a complete revolution. 3. REVOLUTION. I. How we Know the Earth Revolves Around the Sun. This is apparent from the change in the appearance of the heavens in different months. Let a d c dhe the orbit of the earth, and c d a b the sphere of the fixed stars, surrounding the sun in every direction. When the earth is at parently spreading apart, and it is therefore thought that the solar system is moving in that direction. CHAPTER VII. TftB SUCCESSION OF THE SEASONS. r. Causes of the Succession of the Seasons. (i) The earth's revolution round the sun. (2) The inclination of the earth's axis. (3) The unchanging position of the axis. 2 The Inclination of the Earth's Axis. The axis of the earth makes an angle of about 665^° with the plane of the ecliptic — a plane passing through the earth's orbit and the sun's centre. The axis, therefore, leans about 23^° (90° - 66^ ') out of a perpendicular to the plane of the ecliptic. This angle constitutes the inclination of the axis. This mclinatJon is shown in the cut on page 70. The broad line e, which passes around the globe at an equal distance from the top and tlie bottom of the axis, is called the equator. The two points a and b are the poles of the earth, and the imaginary line passing through them is tlie axis upon which the earth rotates. The line a b cuts the orbit or path of the earth round the sun at an angle of 66)^'. ,tl*l«'t.k-h^ ''-... .-v.- iV-'V UN ¥' 70 THE EARTH. Dlasrrftn Showing tho Inclination of the Baitb's Axis. It is a difHciilt matter to explain just what is meant by the plane of the ecliptic. A good way to illustrate it is to suspend a large sphere in water. Then take a ball, through which a knitting-needle has been thrust, to represent the axis, and on which the equator, tropics and polar circles have been carefully drawn, and suspend it also in the water, so that the equator rests on the surface. The surface of the water repre- sents the plane of the ecliptic, and in this position the latter corresponds exactly with the plane of the equator. Now incline the axis until the surface of the water just touches the tropics. It will be found that the inclination of the axis is 231-^. This shews the true relative position of the earth and the plane of the ecliptic. See the cut on page 39. 3. Proof of the Inclination of the Axis. We know that on the 2Tst of June the sun shines vertically on the Tropic of Cancer, while on the 21st < t UN THE SUCCESSION OF THE SEASONS. n of December it shines vertically on the Tropic of Capricorn. This apparent movement of the sun from north to south is proof of the inclination of the axis, and, since these tropics are 23^4° north and south of the equator respectively, we at once see that the inchnation must be 23^^" from the perpen- dicular to the plane of the earth's orbit — ih^ plane of the ecliptic. 4. The Unchang^ing Position of the Axis. Nature reveals nothing more permanent than the parallelism &f the axis of rotation of any rapidly turn- ing body. A top never falls so long as it spins, since its tendency to keep the differient positions of its axis of rotation parallel is greater than the attraction of the earth. A slater, wishing to throw a slate from the roof to the ground, whirls it perpendicularly, and it strikes on its edge without breaking. Even a boy knows that his hoop will not fall so long as he keep;, it rotating rapidly. This wonderful law would lead us to suppose that the axis of the earth must always point in the same direction, even if we did not know it from direct observation. But since we always see the north star, summer and winter, at the same distance above the northern horizon, while all other stars seem to move from east to west, we at once conclude that the axis of the earth must point constantly to the north star. The north star must be imagined at an immense dis- tance from the earth, so that the different positions of the 8xis of the earth, although parallel, will, like the parallel lines of a railway track, appear to meet in a single point in the distance. i ^ 72 THE EARTH. it I 5. The True North. The axis of the earth does not point exactly to the north star, but to the po/e of the heavens, which is one and a third degrees, or two and a half times the diameter of the moon, from it. The result is that the pole star appears to move in a small circle, five times the width of the moon in diameter, with the pole of the heavens as a centre. Therefore twice each day Polaris marks the true north. X m • * ''"•G ^ '-'"h • *' K "' ■1 \ \ \ The Lai ■ '■■■ i Tbc True Pole. In the year 2100, A.D., Polaris will be only half a degree, or about the apparent diameter of the moon, from the pole, and will then slowly pass away from it, until, 12,000 years hence, the brilliant star Vega will fulfil the office of pole star for those who shall then live on the earth. I I «n 74 THE EARTH. l! ; ! 6. Diagram Showing the Change of Sea- sons. (See cut on preceding page.) The average distance of the sun from the earth is 93,000,000 of miles. But, as the orbit of the earth i.s an eilipse with the sun placed in one focus, the earth approaches the sun at certain seasons and draws away from it at others. The earth is the nearest the sun about the 31st of December. This point in the earth's orbit is called perihelion {peri^ near ; and helioSy the sim). The earth is farthest from the sun about the 8th of July. This point in the earth's orbit is called aphelion {ap^ from ; helios, the sun). At [)erihelion the earth is 3,000,000 of miles nearer the sun than it is at aphelion. 7 Vernal Equinox, 22nd March, sun enters Aries. If on ^he 22nd of March the vertical rays of the sun cou, .1 leave a golden line on the earth as it rotates, tbey would mark the equator. Neither pole of the earth inclines towards or from the sun, but sidewise. The suns light reaches to the north and to the south pole. Each hemisphere receives an equal portion of the sun's light and heat. jjfOfl TH£ftNMpST ""/?"av''s _yfff T>C4i _$0U THeRNMOSr BAYS Earth at Vernal Equinox (after Jackson). ipw THE SUCCESSION OF THE SEASONS. 75 The Circle of Illumination—the line dividing light from darkness — passes through the north and south poles, cutting the tciuator at right angles, and, there- fore, bisecting it and all the parallels of latitude, thus giving equal day and night all over the world. It is spring in the northern and autumn in the southern hemisphere. As the earth moves on, tlje north pole begins to lean towards the sun and the south pole from it ; the sun, therefore, shines vertically farther and farther north each day. 8. Summer Solstice, 21st of June, sun enters Cancer. The vertical rays of the sun would now mark the Tropic of Cancer. The north pole leans directly towards the sun, and the south pole directly from it. The sun is at his greatest northern declination ; that is, he ascends the highest he is ever seen above our horizon, and ap- parently rises north of east and sets north of west. NORTH iflNMOSr PAYS ve/fffCAL RAYS Garth at Summer Solstice (after Jackson). ' The sun now seems to stand still in his northern and his southern course ; hence the name Solstice I 76 THK EARTH. \ I {So/, the sun ; sh^ I stand). The northernmost ray of the sun reachts 23^^ beyond the north pole, and would, it it Icfr a golden track, mark the Arctic Circle as the earth rotates, rhe southernmost ray falls 2 3 f/^" short of the south pole, and would mark the Antarctic Circle. The Circle of Illumination passes from the Arctic Circle to the Antarctic Circle, cutting the ecjuator at an acute angle, thus bisecting it, but cutting every parallel of latitude into two unequal parts. This gives une(|ual day and night all ovtt the earth except at the equator. The northern hemisphere receives more thaji half the sun's light ; herice the days are long in the northern and short in the southern. It is simimer in the northern and winter in the southern hemisphere. No ptoint on the Arctic (Circle passes out of the .sun- light, and no point on the Antarctic Circle passes into the sunlight, during the earth's rotation; hence there is a 24- hour day on the Arctic Circle and a 24- hour night on the Antarctic Circle. It is the noon of the 6-month day at the north ])ole and the midnight of the 6-month night at the south pole. As the earth moves on in its orbit, the poles incline less and less towards and from the sun, and the sun's vertical rays fall farther and farther south. 9. Autumnal Equinox, 22nd of September, sun enters Libra. The vertical rays of the sun would again mark out the Ef]uator. All the phenomena of the Vernal Equinox are re- peated, except that it is autumn in the northern and spring in the .southern hemisphere. THE SUCCESSION OF THE SEASONS. 77 ^ hAYk""' MAYS ^^ Rarth at Autumnal Equinox (after Jackaon). As the earth passes on in its orbit, tfie north pole begins to incUne from the sun and the south pole towards it; the sun, therefore, shines vertically farther and farther south each day. 10, Winter Solstice, 21st of December, sun enters Capricomiis. The vertical rays of the sun would now mark the Tropic of Capricorn. The north pole leans directly from the sun, and the south pole directly towards 'the sun. The sun is NOf^THeRNMOST ^ii-i rays" VERTICAL RAYS S0UTH£f9SM0ST RAYS Earth at Winter Solstice (after Jackson). rn^Ku "8 THE >:arth* i ^ at his greatest southern declination ; that is, he de- scends the lowest tie is ever seen, and rises south of east and sets south of west. The sun again seems to stand still. The southern- most ray of tlvi sun reaches 23)^" beyond the south pole, aid marks thv=! Antarctic Circle. The northern- most ray falls 2 3}'2** short of the north pole and marks the Arctic Circle. The Circle of Illumination occupies a similar posi- tion to that at the Summer Solstice, only the condi- tions are reversed. The southern hemisphere receives more than half the sun's light ; hence the days are long in the southern and short in the northern hemi- spheres. It is summer m the southern and winter in the northern hemisphere. No point on the Antarctic Circle passes out of the sunlight, and no point on the Arctic Circle passes into the sunlight ; hence there is a 24-hoar day on the Antarctic Circle and a 24-hour night on the Arctic Circle. It is the noon of the 6-month day at the south pole and the midnight of the 6-month nignt at the north pole. We have now traced the yearU path of the earth, and noticed the course of the succeeding seasons and the varying lengths of day and night. The same series have been repeated through the ages of the past, and will be repeated in the time to come. II. Seasotlfe at the Equator. Since the sun crosses the equinoctial twice during each year, there are two summers and two winters at the equator annually. Winter at the equator, of course, is much warmer than our warmest summer. i THE SUCCESSION OF THE SEASONS. 79 Practically the only seasons known in tropical climates are the "wet' and the "dry.'' J !. Summer Longer Than Winter. As the sun is not in the centre of the earth's orbit, but ^,t one of its foci, the earth from the time of the Vernal Equinox to the time of the Autumnal Equinox passes through more than one-half of its orbit. Also, as was shown in vSection 5, Chapter 6, the velocity of the earth as it passes over this portion of its orbit is less than its velocity while passing over the shorter portion The result is that the time from Spring to Autumn is shorter by eight days than the time from Autumn to Spring. 13. Vertical and Oblique Sun. We have already seen that the vertical rays of the sun move from the Tropic of Cancer at the Summer Solstice to the Tropic of Capricorn at the Winter Solstice. ^ WRECTlOh Of SUN AT THt tQUmOxES Direction of the 5un'» Rmy at Equinoxes and SolAtice*. mmm I So THE EARTH. The result of this will be clearly seen. At the Summer Solstice the northern hemisphere will receive the vertical rays of the sun, and at the Winter Solstice the southern hemisphere will receive these vertical rays. Hov\' great is the difference between the heat from vertical rays and that from oblique rays may be readily seen from the following diagram. Vertical and Oblique Raya. Let A represent a beam from the sun as it strikes the equator at the Vernal Efjuinox ; that is, verti- cally. Then B will represent a beam, from the sun strik- ing the earth at 30" noith latitude at the same time, * THE SUCCESSION OF THE SEASONS. Si ■' ■h':^ Cat ss"* north latitude, D at 65" north latitude, E at 85" north latitude. We at once see that the vertical beam A must bring more heat to the portion of the earth on which it falls than the oblique beams B, C, 1), E. For, while all the beams, as represented in the drawing, are the same breadth, the whole ot the beam A will be concentrated on the small space ot ground num- bered I ; the beam B, however, will be spread out over a much greater space marked 2 ; wliile C, D, E fall upon the still wider spaces marked 3, 4 and 5 - that is to say, the heat of an oblique beam will be spread out over a much larger surface than that affected by the vertical beam. The heat of the beam B is ^, of C i^, of D ^, and of E yj^ of the heat which the beam A brings to any one point. Thus we see that the heat of any part of the earth's sur- face will depend upon the angle at which tiie sun's rays I 'ke it. 14. The Hottest and the Coldest Day. Although the most direct rays fall at noon, the warmest part of the day is usually about 2 p.m. So we do not have our greatest heat at the time of the Summer Solstice, nor our greatest cold at the Winter Solstice. After the 2 1 st of June the earth continues to receive more heat daring the day than it loses during the night. Thus the great heat of an August day is not the result of the sun's heat for that day, but is the result of the accumulation of the heat of the pre- ceding weeks. Thus, also, after the 21st of Decem- ber the earth continues to lose more heat dunng the night than it receives during the day, and the greatest cold does not arrive until some time in January. 82 THE EARTH. i 15. Earth's Axis Perpendicular to the Plane of the Ecliptic. Then the plane of the ecliptic would coincide with the equator. The sun would always shine vertically on the equator. '^. -— .. f^- ! Axis Perpendicular to Ecliptic. He would rise and set every day at the same points on the horizon. His northernmost ray would just reach the north pole ; his souiuernmost ray, the south pole. There would be equal day and night all over the world. Near the equator there would be a fierce torrid heat, while north and south the climate would change into temperate spring, and, lastly, into the rigors of a perpetual winter. There could be no succession of seascxis. 16. Earth's Axis Parallel to the Plane of the Ecliptic. To a person standing on the e lator, the sun would, after passing the Vernal Equmox, each day perform a smaller circle, and, rising like the threads of a screw, reach the north pole at the time of the THE SUCCESSION OF THE SEASONS. 83 ! Summer Solstice. Here he would halt, and then day by day descend the same curve in an inverse manner. >^ Ar^s Parallel to the Piiine of the BcUptlc. In our own latitude the sun would make his diurnal rotations as described above. His rays would pass farther and farther beyond the north pole, until we would be in the region of perpetual day. The sun would then ascend in a ^.piral course to the north pole, and halting would commence to descend by travelling down the same spiral in an inverse manner. As a result every part of the earth would be ex- posed part of the year to torrid heat and six months afterwards to frigid cold. ' 17. Conclusiotz. We have now seen that the succession of seasons is due to the different angles at which the sun's rays strike the earth. They beat on us almost directly at midsummer, and fall very obliquely at midwinter. I mmm li« «4 THE EARTH. We have also learned that these differences in direc- tion are caused by the three things mentioned at the beginning of this chapter, viz : — (i) The revolution of the earth around the sun. (2) The inclination of the earth's axis, at an angle of 2^}4^ from the perpendicular to the plane of its orbit. (3) The parallelism of the axis at every part of the earth's path. All these three are necessary to produce a suc- cession of seasons. For example, (i) and (3) are assumed in paragraph 1 5 ; still no succession of sea- sons is the result. Then, by a simple experiment with a ball or apple, you may easily prove that (i) and (2) may be assumed with a similar result. CHAPTER VIII. THE VARIATION IN THE LENQTM OF DAY AND NIQHT. The variation in the length of day and night has been very fully explained in Chapter VII. Here it would be well to summarize the facts. X. Causes. The causes of the variation in the length of day and night are the same as the causes of the succession of seasons. All three must be given. 2. Maximum Length of Day and Night. Since, as has been stated in Chapter VII., the VARIATION IN LENGTH OF DAY AND NIGHT. 85 ^ Circle of Illumination always bisects the equator, giving half of it light and half of it darkness, there must be equal day and night at the equator during the entire year. The longest day at the Tropics is 13^^ hours, at the Polar Circles 24 hours and at the Poles 6 months. The following table gives a detailed view of the length of the longest day over the whole world : At degree of Greatest Itngth At degree of Greatest length latitude of day is latitude of day is 0.0 12.0 hours 65.8 22.0 hours 23-5 ^•5 " 66.5 24.0 " 30.8 14.0 " 67.4 I month 4 .0 16.0 " 73-7 3 months 5^-S 18.0 " 84.1 5 " . 634 20.0 " 90.0 6 3. Curious Appearances of the Sun. We know that the longer the day the farther north the sun appears to rise and set, and the longer the arch he describes in the sky. Continuing this, the sun would linr^ly rise in the north and set in the north, describing a circle set obliquely in the sky, its northern edge resting on, and its southern edge rising 47** above, the horizon. This is the appearance of the sun to a man standing on the Arctic Circle at the Summer Solstice. His day is 24 hours in length. At midnight on the 20th of June t* ^ sun is seen to rise due north, and at midnight of the 21st he sinks from sight in the same place. To a person standing near the north pole on the 22nd of March the sun appears .0 sweep horizontally around the sky in '?4 hours. During the following I 86 THE EARTH. days this journey is repeated without any perceptible variation in the sun's distance from the horizon. It is, however, slowly rising until, on the 21st of June, it has reached an altitude of 23}^ ^. Here it begins to slowly descend, its track being represented by a screw with a very fine thread. On the 22nd of Sep- tember it again slowly sweeps around the sky, with its face half hidden below the icy sea. The ordinary notion of the polar night needs some correction. It is true that the sun is below the hori- zon for nearly six months. But the duration of twi- light is a matter not to be forgotten. In fact, the autumn and the spring twilights are protracted over 2)^ months each, leaving only 6 or 7 weeks of absolute darkness. Also, since in high latitudes the moon, during its full phase, shines continually above the horizon, and, since the moon must ** full " at least twice during the six weeks of darkness, the period of absolute night is reduced to about three weeks at the most. \ CHAPTER IX. THE ZONES. The division of the surface of the earth in astronomical zones is a matter of very little im- portance. The discussion of climatic zones fdls under the province of physical geography. I. The Zones. The astronomical zones are five belts into which the surface of the earth is divided by the Tropics and the Polar Circles. IHE ZONiib. 87 2 Names and Boundaries. (a) Torrid Zone (I.at., lorridus^ hot) is the belt be- tween the Tropirs of Cancer and Capricorn, and is, ♦herefore, 47"^ wide. (<^) Two TemHrate Zones He between the Tropics and the Polar Civcles, and are each 43 ** wide. (c) Two Frigid Zones (Ivat , fri^idus^ cold) li^.: with- in the Polar Circles, and have a r lius of 23)^'', 3. Characteristics of the Zones. (a) T'>rrid Zone — (i) scorching neat ; (2) sun verti- cal over every place twice a year ; (3) days and nights differ in length very little during the year ; (4) vcj^e/a- Hon is luxuriant; (5) animal //'/ c^». ■ ■P^. '^ ^^" f* a^ ///. Photographic Sciences Corporation 23 WEST MAIN STREET WEBSTER, NY \45P0 (716) 872-4503 -r iV iV v .^ -<•' ^ o^ Q, I longer and longer as we approach the poles. The length of a degree of latitude on the equator is 68^ statute miles. In southern Canada it is 69 miles, and at the pole 69^ miles. The figure below shows •the reason for this difference. D«ffrees Orow Longer (After Todd). 4. Length of a Degree of Longitude. Measured at the equator the length of a degree of longitude is nearly the same as the length of a degree of latitude. It would be the same were the circum- ference of the earth at the equator the same as the circumference of the earth drawn through the poles. It has been found to be 69.07 miles at the equator, and, since all the meridians meet at the poles, it fol- lows that a degree of longitude has no length at the poles. The following table shows the length of a degree of longitude for every five degrees of latitude in statute miles : » LATITUDE, LONGITUDE AND TIME. 91 1 Degret of Statuts Degree el Statute iatttmU miles latitude miles 69.07 50 44-35 5 68.81 55 3958 10 67.95 60 34-53 «S 66.65 65 29.15 20 64.84 70 23.60 «s 62.53 75 17.86 30 59.75 80 11.98 35 56-51 85 6.00 40 52-85 • 90 .00 45 48.78 5. How to Find the Latitude of a Place. (a) By means of the sextant find the elevation of the pole star above the horizon. This gives the lati- tude at once. (p) By means of the sextant find the elevation of the sun above the horizon at noon. From a Nautical Almanac find the declination (distance from the equator) of the sun for that day. If the sun is north of the equator, and the observer in the northern hemisphere, subtract this declination from the sun's elevation, and it will give the height of the sun if the sun were at the equator. Subtract this from 90*^, and the remainder is the latitude. If the sun is south of the equator its declination must be added to its observed elevation. 6. How to Find the Longitude of a Place. (rt) By means of the sextant mark the time when the sun ceases to rise any higher in the heavens. It is then apparent noon. Add or subtract the equation of time (the number of minutes the sun is too fast or wmmmm 92 THE EARTH. too slow ; see Chapter VI., Section 3) as found in the Nautical Almanac, and the true or mean noon is found. Compare tliis local time with the time of Greenwich, as found from the ship's chronometer, and by reducing the difference of time to degrees, the longitude is found. The earth turns 360 ** in 24 hours, or 1° in ^Jy hour=4 minutes. That is, a difference of four min- utes in time is equivalent to a difference of one de- gree of longitude. (d) This is an unsafe way of determining longitude, because all depends upon the accuracy of the chronometer. Therefore, the navigator prefers to depend upon the moon. The Nautical Almanac gives, for three years ahead, the distance of the moon from the principal fixed stars which lie along its path, at every hour (Greenwich time) of the night The sailor then determines with his sextant the moon's distance from a certain fixed star, and then, by refer- ence to his almanac, finds the corresponding Green- wich time. By comparing this with his local time, and reducing the difference to degrees, he has his longitude, as before. 7. Time. (a) Sidereal time has been fully discussed. (See Chapter VI., Section 3). This is the only absolutely correct time. Astronomical clocks are regulated to keep sidereal time. {b) Solar time has also been fully discussed in Chapter VI , Section 3. Mean Solar time is kept by our ordinary clocks. A Sun-Dial gives the apparent time, which may be readily changed to mean time by I. . LATITUDE, LONGITUDE AND TIME. 9$ mmm adding or subtracting the number of minutes the sun is too fast or too slow, as; shown in the almanac. (i) Standard time has been adopted as a matter of convenience. When each place kept its own local time, the annoyance in travelling from place to place was very great. Therefore, in November, 1883, it was decided to establish a standard of time by which railroad trains should run and all ordinary affairs be regulated. 'v^rf'^^matTm y Tim* all over the World when It Ia Noon at Greenwich (after Tudd;. By thi^ arrangement the North American continent is divided into five sections or belts, approximately 15 degrees of longitude in width, so that the time of each varies from those adjacent to it by exactly one hour. Commencing at the east, these divisions keep Colonial Time, or the time of the 60th meridian ; Eastern Time, or the time of the 75th meridian; Central Time, or the time of the 90th meridian ; Mountain I'ime, or the time of the 165th meridian ; 94 THE JEARTH. Pacific Time, or the time of the 120th meridian. This facilitates matters very much. All that is neces- sary in travelling is to change your watch one hour when passing from one of these divisions into another, setting it ahead when travelling east, and turning it back when travelling west. 8. The Calendar. There are two calendars in use at the present day. Russia and Greece still employ the Julian Calendar. AU other modern nations have adopted the Gregorian Calendar. The history and differences Qf these calendars are as follows : (a) The Julian Calendar is named after Julius Caesar, who, B C. 46, reformed the calendar by the aid ot* Sosigenes, an Egyptian astronomer. Sosigenes knew the true year was composed of about 365 1/ days, so Caesar decreed that three successive years ( f 365 days should be followed by a year of 366 days perpetually. This would have needed no correction, but for the fact that this Julian year was 1 1.2 minutes too long. This accumulated year by year, until in 1582 the error amounted to ten days. In that year the vernal equinox occurred 'on the 11th of March instead of the 21st. (/^) The Gregorian Calendar^ which was adopted by England in the year 1752, is named after Pope Gregory. He reformed the Julian Calendar by drop- ping 10 days and ordering that three leap year days be omitted in every four centuries. Thus, although every year not marking the close of a oentury is a leap year if its number is divisible by four, the cen- turial years, as 500, 600, 700, 800, are leap years only when exactly divisible by 400, I t \:i-: ■ , M.r •. Supplementary Exercises ARITHMETIC ARITHMETIC EXERCISES FOR FIRST CLASS Teachers' Edition, 15c. ARITHMETIC EXERCISES FOR SECOND CLASS Teachers* Edition, 15c.; Pupils' Edition. 10c. ARITHMETIC EXERCISES FOR THIRD CLASS Teachers' Edition, 15c.; Pupils' Edition, 10c. ARITHMETIC EXERCISES FOR FOURTH CLASS Teachers' Edition, 15c.; Pupils' Edition, 10c ARITHMETIC EXERCISES FOR FIFTH CLASS Teachers' Edition, 15c.; Pupils' Editio:^ tOc. MENTAL ARITHMETIC— PART I. For 1st, 2nd and 3rd Classes, 10c- MENTAL ARITHMETIC— PART II. For 4th and 5th Classes, 10c. DRILL ARITHMETIC FOR ALL CLASSES Teachers' Edition, 15c.: Pupils Edition. 10c. GRAMMAR EXERCISES IN GRAMMAR For 3rd, 4th and 5th Classes, lOc HARD PLACES IIS GRAMMAR MADE EASY For 5th Classes and High Schools, 30c. T Supplementary Exercises COMPOSITION JUNIOR LANQUAQE LESSONS For 1st, 2nd and 3rd Classes, lie. EXERCISES IN COMPOSITION For 4th and 5th Classes, lOc. MANUAL OP PUNCTUATION For 4th and 5th Classes, lOc. GEOGRAPHY QEOQRAPHY NOTES For 3rd, 4th and 5th Classes, 10c. ASTRONOMICAL AND MATHEMATICAL QEOQRAPHY For 5th Classes and High Schools, 28c. HOW WE ARE GOVERNED For 3rd, 4th and 5th Classes, 10c. MAP OF CANALS. 10c. HISTORY BRITISH HISTORY NOTES, 10c. CANADIAN HISTORY NOTES, lOc ROMAN HISTORY IN BRIEF, I5c. QR^EK HISTORY IN BRIEF, 15c. SUMMARY OF CANADIAN HISTORY IN VERSE, Sc. T