LB 0% w I AND MAPS A TEACHERS MANUAL mm CM IB W'■ * * / ~k * * / Big Dipper. / / *^ / / / / / / / / / / / / / / / i f Jj tartk's Plant of f J , ar tt'i grftg The earth. The 8Un Fig. 2. Finding the North Star Globes and Maps in Elementary Schools 17 Two stars in the Big Dipper opposite the handle indi- cate the direction toward the North Star, which, though not very bright, is the first very noticeable star in line. (Fig. 2.) Two motions. Hold the globe level with the mimic sun, incline the axis toward the north somewhat. Rotate it as described under Rotation on page 14, and pass it around the sun in a direction opposite to that taken by the hands of a watch held face up, and with the axis all the while pointing toward the north. This represents one complete circuit around the sun, which requires one year. The path taken by the earth is called its orbit. As seen from the earth, the sun appears to be following the same path, and this apparent course of the sun is called the ecliptic. (Fig. 4.) Plane of earths orbit. A plane is a perfectly flat surface, real or imaginary. It may be represented by the side of any smooth, flat object. A plane has length and width but no thickness. Now imagine a plane which passes through the center of the sun and the center of the earth, and extends far in every direction. As the earth revolves around the sun, the center of it lies con- tinually in such a plane; in other words, every part of the earth's course lies in what is called the plane of its orbit. (Fig. 5 or 6.) Angle of inclination of earth's axis. Explain that circles are used to measure angles. Draw a quarter circle on the blackboard and draw thereon straight lines to illustrate various angles, as, 30 , 45 , 6o°, 66^°, 90 . An angle of 90 is called a right angle. Note that a line making an angle of 66^° with the base is inclined 23}^° from the perpendicular, and so illustrates the position of the earth's axis. (90 — 66^° = 23^°.) Place the axis of the globe 18 Globes and Maps in Elementary Schools IS" from % base or 73" from.perptt dicular Base Fig. 3. A quadrant, or one fourth of a circle. The oblique lines indicate various angles with the base. The heavy line indicates the inclination of the earth's axis as compared with the plane of its orbit, which is represented by the base wholly in the plane of its orbit as nearly as may be; vertical to the plane. Incline the axis toward the north and 23J4 from the vertical position. This is approxi- mately the direction which the axis of the earth takes the year round. (Fig. 4.) The axis of a globe having a graduated metallic meridian circle can easily be set at an angle of 23^° from a vertical position, or any other angle, by adjusting the meridian with reference to the attached orbital plane. Day and night and the equinoxes. Call attention to the fact that the apparent passing of the sun across the heavens from east to west is an illusion which deceived Globes and Maps in Elementary Schools 19 the wisest men for ages, and illustrate the first appearance of the sun in the morning to a man standing near your school. Imagine him as standing facing the east with his left hand toward the north and his right hand toward the south. Obviously, if the position of the globe is not correct and it is not rotated in the right direction, the sun will not seem to rise in front of the man. The teacher should make sure about these points before she gives the lesson, and should in advance consult some one who knows if she is doubtful. Show that in the earth's revolution around the sun there comes a time when, owing to the inclination of the earth's axis, the sun's rays meet the earth's surface ver- tically at a point 23^° north of the Equator, and that at the same time they extend 23^° beyond the North Pole while they lack 23^° of reaching the South Pole. (Figs. 5 and 6.) This condition marks the location of three circles on the earth, one 23^° from the North Pole, called the Arctic or North Polar Circle, another 23 y 2 ° from the South Pole«called the Antarctic or South Polar Circle, and a third 23^° north of the Equator called the Tropic of Cancer. The marking of the Tropic of Cancer or either of the other circles may perhaps be more clearly understood if a ray of sunlight be imagined as an immovable pencil with the point touching the earth. Such a pencil would mark a circle at each rotation. The teacher should dwell with patience on these rela- tive positions of the earth and the sun, as they appear on June 2 1 of each year, till the facts are clearly under- stood, for otherwise the causes of the seasons and of long and short days will not be clear. Observe that by a man standing on the Tropic of Cancer on this day, the sun, at noon, is seen directly overhead ; 20 Globes and Maps in Elementary Schools that to one standing north of the Arctic Circle there is no night, the sun being in sight during the entire rotation; that one standing anywhere between the Equator and the Arctic Circle has the day longer than the night; that toward the north the day grows longer and the night shorter; that a man standing south of the Antarctic Circle has no day, the sun being out of sight during the entire rotation; that a man standing anywhere between the equator and the Antarctic Circle has the night longer than the day; that toward the south the night grows longer and the day shorter; and that at any point on the Equator the day and the night are exactly equal. On this date occur the longest day and the shortest night in the Northern Hemisphere, while in the Southern Hemi- sphere occur the shortest day and the longest night. Revolve the earth one fourth the distance around the sun, with the axis still directed toward the north as described, and observe that the direct vertical rays of the sun meet the earth at the Equator, and that the sun- light covers a hemisphere that on the north extends just to the North Pole and on the south just to the South Pole. Observe also that on this day, September 22, the days and nights are equal over the entire earth. This is called the autumn equinox (aequus means equal, nox means night). Revolve the earth another fourth of the distance around the sun, still pointing the axis toward the north. This brings them to a time representing December 2 1 . (Figs 4 and 6.) Observe that the conditions with regard to day and night are exactly the reverse of those which existed on June 21. The sun shines vertically over a point on the earth's surface 23^° south of the Equator and so marks the position of a circle called the Globes and Maps in Elementary Schools 21 Spring* equinox fi Earth aphelionf iSui Earth in -^perihelion '*9 kto: Autumn equinox Fig. 4. Relative positions of the earth and the sun during the spring equinox, the summer solstice, the autumn equinox, and the winter solstice Tropic of Capricorn. North of the Arctic Circle there is continuous night, south of the Antarctic Circle there is continuous day, between the Equator and the Arctic Circle the nights are longer than the days, and between the Equator and the Antarctic Circle the days are longer than the nights. On this date occur the shortest day and the longest night of the year in the Northern Hemi- sphere, while in the Southern Hemisphere occur the longest day and the shortest night. It will be seen that from June 21 to December 21 the days in the Northern 22 Globes and Maps in Elementary Schools Hemisphere have become gradually shorter and the nights correspondingly longer, while on the other hand the days in the Southern Hemisphere have become grad- ually longer and the nights shorter. On the Equator the days and nights are still exactly equal. Observe also that during this period of six months the sun has seemed to move gradually toward the south, daily rising and setting a little lower. Every child in the class has observed the fact that the sun moves lower in the south in winter than in summer, but by the use of the globe both the cause and the effect of this phe- nomenon can be made quite clear. In continuing the revolution of the earth around the sun, lead the pupils to observe that the changes in the lengths of day and night, for the next six months after December 21, are the reverse of those during the pre- ceding six months; that is, north of the Equator the days lengthen and the nights correspondingly shorten, while south of the Equator the days shorten and the nights correspondingly lengthen. Note also that in the posi- tion halfway between that for December 21 and that for June 21, there is a day when again the direct vertical rays of the sun shine upon the Equator and daylight extends over a hemisphere reaching .from the North Pole to the South Pole. This is March 21, the spring equinox. (Fig. 7.) Observe that then again the days and nights over the entire earth are equal. Note fur- ther that on the Equator they have been found equal all the time. At the equinoxes, when the sun seems to move across the Equator, it is said to "cross the line." The horizon. The line where the earth and the sky seem to meet is commonly called the horizon. Scien- tists use the term to indicate (a) the plane passing through ' i? 23 »vi* n 3 }N 24 »p»* vfl*N Globes and Maps in Elementary Schools 25 the eye of the observer at right angles to the vertical at any given point, called the sensible horizon; and (6) the plane passing through the center of the earth parallel to the sensible horizon, called the rational horizon. The solstices. Observe that in the earth's swing around the sun, which we began to study in the position for June 21, it reaches a position halfway around on December 21, and that thereafter it passes upon its return journey. The sun which from day to day had seemed to men on the earth to move toward the south, on that day reaches its farthest limit, and thereafter seems to move toward the north; but on that day it seems to move neither north nor south. Hence the day is called the solstice (sol means sun; sister e means to stand). This is called the winter solstice; there is a similar day on June 21, which is known as the summer solstice. The seasons. Every child knows that the chief source of heat as well as light is the sun. In the study of day and night, light has been a fundamental factor; in a study of the seasons, heat is a fundamental factor. First compare the effects of vertical rays of heat with those of slanting or oblique rays. Distance, of course, affects the intensity of heat, the intensity diminishing as the distance increases, and conversely; but the amount of heat which a surface receives depends also upon the relative direction whence it comes. If, for instance, the rays meet the surface, vertically, it receives far more heat than it would if the rays were very slanting, for it intercepts a far greater number of them. These statements may not be under- stood by the pupils, but they may be made clear by the use of a lamp and a piece of cardboard or any similar 26 Globes and Maps in Elementary Schools apparatus. The broader general truth may be formu- lated somewhat as follows: The more nearly vertical the rays, the greater the heat; and conversely, the more slanting the rays, the less the heat. Again place the globe in the position for June 21, as already described on page 19. (See also Fig. 5.) Observe that the sun's heat rays as well as its light rays meet the earth vertically on the Tropic of Cancer, that they reach the entire Northern Hemisphere, becoming very slanting at the far north, that they become more and more slant- ing from the Tropic of Cancer to the Antarctic Circle, where they cease, and that all south of the Antarctic Circle is shut off from direct rays of heat as well as light. Reason from these observations that it is very warm at that time of year for some distance north and south of the Tropic of Cancer, that it is cold in the region of the North Pole, that it is far colder in the region of the South Pole, and that there is a middle region on both the north and the south where the cli- mate is neither very hot nor very cold. Observe that in June the Northern Hemisphere, having long days and short nights and receiving more directly the heat rays of the sun, must be warmer than the Southern Hemisphere, which has long nights and short days and receives less directly the heat rays of the sun. It is then summer in the Northern Hemisphere and winter in the Southern. June 2 1 would be midsummer in the Northern Hemisphere and midwinter in the southern were it not that, as the earth warms so slowly after winter and cools so slowly after summer, the seasons all lag behind the sun. Hence it is that this date is only the beginning of summer, as the astronomers count it. On passing the globe around the sun again, as before, 27 28 Globes and Maps in Elementary Schools it can be seen that between June 21 and December 21 the conditions with regard to both heat and light become reversed so that on the latter date there is summer in the Southern Hemisphere while there is winter in the Northern. (Figs. 4 and 6.) Midway between these dates, on March 21 and September 22, when the cold of winter on one hand and the heat of summer on the other hand have become moderate, occur the spring or vernal equinox and the autumn equinox, the begin- ning of spring and autumn respectively in the middle latitudes. (Fig. 7.) Winter is said to begin on De- cember 2i f the winter solstice. Observe that as the vertical rays of the sun pass from the Tropic of Cancer to the Tropic of Capricorn and back each year and are never far from the Equator, the region of the Equator must be very warm the year round. The continued exposure to the sun of each frigid zone for months at a time without any night would make it unbearably, even dangerously, hot were it not that the heat rays there meet the surface of the earth very slant- ingly, and so impart little heat. Zones. It will be seen that there are on the earth five broad regions or belts (zones) in each of which the weather conditions (climate) have marked character- istics. There is the very warm belt between the tropics, called the Torrid Zone; there are the two very cold regions about the poles, the one on the north extend- ing south to the Arctic Circle and called the North Frigid Zone, the other on the south extending north to the Antarctic Circle and called the South Frigid Zone; and there are the two intermediate regions called respectively the North Temperate Zone and the South Temperate Zone. (Fig. 6.) Globes and Maps in Elementary Schools 29 An interesting discussion may be started by inquiring what the effect would be if the axis of the earth were perpendicular to the plane of its orbit. Would there be any change of seasons? The following diagram (Fig. 8) indicates the position in which the globe should be held while the pupils are studying the question. Plane of earth 's "orbit tThe earth The sun Fig. 8. The earth shown as it would be if its axis were perpendicular to the plane of the orbit. Distances in miles. To find the distance in miles between any two points on the earth, stretch a narrow strip of writing paper from one to the other as indicated on the globe, and mark the distance on the paper; then measure off the same distance on the Equator where the degrees are numbered, beginning at the prime meridian, and so ascertain the distance in degrees. As one degree on a great circle is 6o£ miles, multiply this number by the number of degrees indicated. If, for instance, they are 6o° apart, they are sixty times 69! miles apart, or 4,150 miles. Along the meridian of 30°W. or else- where, at the intersection of the parallel lines, may be found Arabic numerals. These indicate the length of a degree of longitude on the small circles on which they stand. The sun is about 95,000,000 miles distant. The moon is about 235,000 miles distant, and is about 2,000 miles in diameter. The earth is about 8,000 miles in diameter and about 25,000 miles in circumference. 30 Globes and Maps in Elementary Schools Third Series: For Upper Elementary or Lower Secondary Grades 1 Direction of the sun. Illustrating with a globe, lead pupils to see that to a man standing on the Arctic Circle on June 21, the sun at noon appears rather high in the heavens in the south, that at midnight it is on the hori- zon in the north, and that during the entire twenty- four hours it does not set. Lead them to see that to a man standing at the North Pole on that date it seems merely to swing around the heavens, some distance above the horizon, but all the time in the south. At the North Pole there is no north, east, or west. To people living south of the Equator the sun always appears in the north at noon. When the sun appears to you on the horizon on the morning of June 21, its rays, which then reach you very slantingly, meet the earth vertically at a point on the Tropic of Cancer. (Fig. 5.) At that point it is noon. To determine just where the point is, learn from an al- manac at what time the sun rises at your home. If, for instance, it rises at 4.30 a.m., it will require 7K hours to pass over to your meridian and mark twelve o'clock, noon, for you (1 2 hr. — 4^ hr. = 7^ hr.). As it passes over 15° of longitude in one hr. (see p. 32), in 7 }4 hr. it will pass 1 The following lessons are here inserted for such use as teachers may choose to make of them. The substance of some of them appears in the regular high-school courses in physical geography and astronomy, though they are often pursued with little or no ref- erence to a globe. All treat of topics which every intelligent person wishes to understand. Some or all of them may be given in the upper elementary grades, or they may be given in the advanced grades, or they may be omitted, at the discretion of the teacher. The fact is not to be overlooked that, to be effective, they must be based on actual observation of the globe and of the celestial bodies named. None ot them is intended to give more than the merest simple outline. Globes and Maps in Elementary Schools 31 over 7>£ times 15 , which are 112^°. It is seen there- fore that when the sun first appears to you on that morn- ing, it is shining vertically on the Tropic of Cancer at a point ii2>£ east of your meridian. Suppose your meridian to be 75°W. Then the point referred to ia in longitude 37^° E. Make this clear. (75° + 37K° = 1 1 2%°.) Find the point on the Tropic of Cancer at 37^° E. With a piece of cord mark the most direct line on the globe between your home and that point. This indicates the direction in which on that morning you must look to see the sun rise. You may be surprised to find that you must look toward the northeast, as you may discover by comparing the direction of the cord with the direction of the parallels. In similar manner the direction of the sun at sunset (northwest) or at any other time of day may be found. But in applying this rule it is necessary to know the declination of the sun on the particular date, that is, its distance north or south of the Equator, which varies according to the time of year. The declination on each of the solstices (23^° north or south) and each of the equinoxes (o°) is known. For any other date, see the analemma. If it is remembered that direction east and west on the globe is indicated by the parallels, some idea of the direc- tion of the sun from any point on the earth may be gained from Fig. 5 or 6. To a man traveling north, the North Star seems to rise in the heavens. At the North Pole it would seem to be directly overhead. It is invisible in the Southern Hemisphere. Longitude and time. From any one meridian around the earth directly east or west to the same meridian, as 32 Globes and Maps in Elementary Schools measured on any parallel, there are 360 of distance. In the rotation of the earth, the sun is caused apparently to pass over this distance from east to west in twenty-four hours. In one hour therefore the sun passes over is°(i-24 of 3 6o° = 15°). Noon by the sun arrives at any place when the sun shines vertically on the meridian which passes through that place. It follows that when, for instance, it is noon at any one point, it is 11 a.m. at any other point located 15 west, the sun not having reached it, and it is 1 p.m. at any other point, 15 east, the sun having passed it. It is therefore seen that, toward the west from any point, time by the sun is earlier (slower), while toward the east it is later (faster). The variation is at the rate of one hour for 1 5 , or four minutes for one degree. Note that the meridians are marked along the Equator on the globe in multiples of 15, as 15°, 30 , 45 , etc., thus making it possible easily to find the difference in time between any two meridians. Along the Equator, Roman numerals, clock fashion, may also be found adjacent to the meridians whose num- bers in degrees are divisible by 15. These numerals indi- cate the time on each meridian when it is twelve o'clock on the prime meridian. Find the difference in longitude and in time between two given meridians both of which are in east longitude; between two in west longitude; be- tween two meridians, one of which is east and the other west. Give problems, as: An event happens at 6 p.m. at a point on the prime meridian and the news is sent by telegraph to a point 75 west without loss of time. At what time is the news received at the latter? The difference in longitude is 75 , hence the difference in time is five hours. (75 -5- 15 = 5.) As time toward the west is Globes and Maps in Elementary Schools 33 earlier (slower), the news was received at i p.m. of the same day. For exact measurements a degree is divided into sixty equal parts called minutes (marked ') and each minute is divided into sixty equal parts called seconds (marked ")• Table 60" make i' 60' " i° 360 " 1 circle 1' is one nautical mile. If the difference in time between any two places is given in hours, minutes, and seconds, the difference in longitude may be found by multiplying by 1 5 and calling the result respectively degrees, minutes, and seconds. Time dial. The small, loose metal plate attached to each pole of the globe is a time dial. It is divided into twenty-four equal parts corresponding to the twenty-four hours of the day; generally into two sets of twelve each, marked to correspond to the clock record. By adjusting it to any meridian so as to show the time thereon, the time on any other meridian at the same moment is indi- cated. With this information, the pupil can easily deter- mine the difference in time between the two meridians. Standard or railroad time. If the people in every place reckoned time by the sun, no two whose longitude differ would have the same standard and there would be great confusion. In the latitude of central New York, a difference of about eleven miles, east and west, makes a difference of one minute in time by the sun. Difference in location north and south makes no difference in time. Why? A man whose watch is correct for his home would find it one minute slow if he were to go eleven miles to- ward the east or one minute fast if he were to go eleven miles toward the west. After traveling any considerable 34 Globes and Maps in Elementary Schools distance east or west, no man could learn the exact local time by consulting his watch. Watches and clocks would be of less use, railroad trains could not be run safely, and time-tables would lose most of their value. Business would be seriously hampered. All inconvenience and loss on this account are avoided by the adoption in America and elsewhere of a simple expedient called standard or railroad time. This is based on the knowledge that a difference of 15 in longitude makes a difference of one hour in time, and on the convenience of counting no changes of time except in full hours. The meridian of 7 5 W. , which passes through the middle of the state of New York, differs from the prime meridian in time exactly five hours. The meridiafcpf 90 W. differs six hours; of 105 W., seven hours; of ir^ W., eight hours. The plan is to give to all the territory in the region of each meridian whose number in degrees is divisible by 1 5 the time of that meridian. For instance, when it is twelve o'clock, noon, on the 75th meridian, it is counted twelve o'clock over a region halfway to the 60th meridian on the east and halfway to the 90th meridian on the west. By this plan, the United States is divided into four time- belts or zones extending north and south, the middle of each being marked by one of the four meridians just mentioned. A traveler in the United States therefore takes no account of any change in time unless he passes into another time-zone, and then the change is exactly one hour. For illustration, if he is going west, and his watch indicates four o'clock on passing into the next time- zone, he knows that by standard time it is there three o'clock. On the other hand, if he is going east and his watch indicates four o'clock on passing into the next time- zone, he knows that by standard time it is there five o'clock. Globes and Maps in Elementary Schools 35 Time is spoken of as Eastern, Central, Mountain, or Pacific according as the zone had in mind is marked by the meridian of 75 , 90 , 105 , or 115 . In practice, the boundaries between the zones are irregular. International date line and days of the week. Hold the globe so as to represent noon at your home, say 75 W. Call the day, let us say, Monday. Now rotate the globe properly and note that as each successive meridian passes under the vertical sun it is Monday noon on that meridian. When your home again passes under the vertical sun, it is again noon there, but what day? You who have remained at home will say, Tuesday. Then when and where was the change made from Monday to Tuesday? By agreement between civilized nations a line has been chosen where such changes can be made with least incon- venience, and that line is the meridian of 180 , exactly opposite the prime meridian, and passing through the Pacific Ocean, where fewest people live. It is called the International Date Line. Find it on the globe, and observe that in some places it is drawn to one side of the direct course. These diversions of it have been agreed upon to accommodate the people who live on the islands included. So when the line passes the vertical sun on Monday noon as just seen, the people on the west side of it immediately begin to call the time Tuesday noon. Place the globe in a position to represent noon on the prime meridian (Greenwich), call the day Monday, and trace the day both eastward and westward. At the longitude of qo°E. the sun is just passing out of sight; it is sunset. Farther east it is evening, Monday evening, while just west of the Date Line it is nearly midnight at the end of Monday. On the other hand, at the longitude of 90 W. the sun is just rising on Monday morning, while 36 Globes and Maps in Elementary Schools farther west and near the Date Line it is very early in the morning of Monday. It will be seen therefore that at the moment when it is noon on the prime meridian it is mid- night on the Date Line, that Monday is just beginning immediately at the east of the line while it is almost ended immediately at the west of the line. Over the whole earth it is Monday, and both the beginning and the end of that day occur on the Date Line. If the globe be rotated ever so little so as to bring the prime meridian past noon, midnight, which marks the division between two days, moves to the west of the Date Line a corresponding distance. As Monday was ended on the Date Line at midnight, the next moment Tuesday begins right there. Rotate the globe still farther and observe the effect. When it is noon 15 W. it is midnight (Monday-Tuesday) 1 5 west of the Date Line, which is the same as 165° E. (i8o°-i5° = i65°). It is then one o'clock Monday after- noon on the prime meridian, while on the Date Line it is either one o'clock in the early morning of Monday or one o'clock in the early morning of Tuesday, according to whether it is considered from the east side or from the west. If a traveler going westward could at that moment stand on the east side of the Date Line, to him it is 1 a.m. Monday; but the instant he steps across the line, to him it is 1 a.m. Tuesday. So he would be obliged to add a day to his reckoning. This is precisely what all seamen do who are sailing westward. In a similar manner it may be shown that travelers going east must subtract a day on crossing the Date Line. For instance, if the ship, going east, reaches the Date Line on Tuesday at 8 a.m., the seamen immediately change their record to 8 a.m. Monday. From the foregoing it will be seen that there may be Globes and Maps in Elementary Schools 37 two consecutive days of the week on the earth at the same time, and it may easily be shown that as the later, beginning at the Date Line, spreads steadily over the whole earth the earlier recedes before it and vanishes at the Date Line at midnight. When it is noon on the Date Line the earth is divided equally between two days. Lead pupils to see that from the moment when a day begins at midnight on the 180th meridian to the moment when it ends in the same place, forty-eight hours must elapse, and the earth must make two complete rota- tions. At the end of the first rotation, the day covers the entire earth. A.M. and P.M. The day as here meant is the mean solar day of twenty-four hours as measured by the clock. Solar days vary in length, as will be seen by reference to the paragraphs on The Analemma. The mean solar day is found by adding together the exact lengths of all the solar days in the year and dividing the sum by the number of days in the year. Each day of the week is reckoned from midnight to midnight. As now commonly made, clocks keep a record for twelve hours only and then re- peat. This makes it necessary to add an extra description to distinguish any two points of time in each of the two series for the day. For instance, eight o'clock is de- scribed as 8 a.m. (eight ante meridiem; ante means before, meridiem means midday, noon), or 8 p.m. (eight post meridiem; post means after) 8 a.m. means not eight hours before noon, but the eight by the clock which comes before noon. Clocks have been made to record time in series of twenty-four hours, but they are not common. Ocean currents- Observe that the waters of the oceans fiow about in regular and well marked currents. Trace the courses of a few of the most noticeable. Give 38 Globes and Maps in Elementary Schools particular attention to the famous Gulf Stream, which pours a vast volume of warm water from the tropical region northward along the east coast of the United States, thence diagonally across the ocean to the British Isles and Norway. What effect has this on the climate of those European countries? Note also the Labrador current, which brings icy water south from the Arctic region. What effect has this on the climate of Labrador? Ocean cables. Observe the courses of the principal ocean telegraph cables. Isotherms. An isotherm (iso means equal or same, therm means heat) is a line that connects places on the earth's surface that have the same temperature at a given time or that have the same average or mean temperature during the same period. Observe the isothermal lines on the globe. There may be two sets, one for January and one for July. It will be seen that latitude (distance from the equator) does not alone govern the temperature of any place. Elevation above the sea, distance from the sea, the character of ocean currents that are near, and other conditions are factors that also affect the temperature. Observe particularly the isothermal lines that cross the United States. For instance, the line for January (winter) that passes through New York City and shows an average temperature of 3o a , passes northeastward to Iceland and northern Norway, within the Frigid Zone, and, on the other hand, after dipping southward to Missouri, passes far to the northwest in southern Alaska. In January, therefore, these places all have the same temperature, and Iceland and southern Alaska are as warm as New York City. The land is then relatively colder than the sea. But in summer the conditions are different, so that in the same latitudes the land is warmer than the sea. For Globes and Maps in Elementary Schools 39 illustration, trace the isothermal line for July (summer) which passes through Boston, and shows an average temperature of 70 . Note that it passes far to the north- west into Canada, and then dips to the south opposite northern Mexico. Earth's orbit elliptical. Stick two pins into a piece of cardboard one-half inch apart. Take a piece of cord 4^ inches long, and, after tying the ends together, lay it around the pins on the cardboard. Next, with a pencil draw the cord tightly to one side, and trace a line around both pins as far from them as the cord will permit. The figure so drawn is an ellipse, and the pinholes are the foci (singular, focus; plural, forci). The earth's orbit is an ellipse and the sun is one of the foci. It follows that the earth is nearer the sun in one part of its course than else- where. When it is nearest it is said to be in perihelion (peri means around; helios means sun), and when it is farthest away it is said to be in aphelion (a means from). Perihelion occurs in the northern winter and aphelion in the northern summer. 1 Attach a piece of cord to a weight and swing the latter around with differing lengths. Observe that the shorter the cord the swifter the circuits of the weight. This will illustrate the fact that the earth swings fastest when in perihelion, and slowest when it is in aphelion. The analemma. The large diagram like a figure 8 on the globe is called the analemma, and it presents certain facts about the earth in its elliptical course around the sun. If it is to be understood, therefore, the pupils should, in consulting it, constantly bear in mind (or, better, illus- trate) the relative position of the earth in its orbit. It is useful for two purposes. First, it shows the declina- tion of the sun, that is, its distance north or south of the 40 Globes and Maps in Elementary Schools celestial equator day by day during the year, or, what is practically the same thing, the latitude at which on each day its vertical rays meet the earth. The celestial equator is an imaginary circle in the heavens directly above the terrestrial (earthly) Equator. As the sun never shines vertically beyond the tropics, it will be observed that the analemma extends only from one tropic to the other, that is, from 23^° N. to 23^° S. Note that on the margin of the diagram are the names of the months and a scale to indicate every day of each month. Observe that the marginal scales change sides where the two loops meet. The mark for each day indicates the exact position of the parallel on which the sun shines vertically at the time. For instance, both March 21 and September 2 1 appear on the Equator, showing that on those dates the sun shines vertically on that circle. (See The Equinoxes.) Again, June 2 1 appears on the Tropic of Cancer, and December 21 on the Tropic of Capricorn, showing the circles which receive the vertical rays on those dates. On the former date the declination of the sun is said to be 23^° N.; on the latter, 23^° S. The latitude of the sun for any particular date may be found by using a metallic or a flexible meridian having a scale of degrees to measure north or south from the Equator, or, for illustrative purposes, by estimating the latitude as compared with a known parallel. Observe that in some months the sun seems to move north or south rapidly, the spaces for months and days, as in March and October, being wide, while in others it moves north or south very slowly, as in June and December. In the latter months occur the solstices. (See The Solstices.) Second, the analemma shows certain interesting facts about time as indicated by the sun and by a good clock. Globes and Maps in Elementary Schools 41 To begin with, if the earth merely rotated around its axis and did not revolve around the sun, one day would measure exactly one rotation; but because the earth swings around the sun, it is constantly changing its position, so that, counting from exact noon on any meridian, one rotation will not quite bring the same meridian under the sun, the earth having moved farther around in its orbit. From noon on any meridian, therefore, till noon the next day, the earth makes a little more than one rotation. A day as thus measured by the sun is called a solar day (sol means sun). Bearing in mind that when in or near perihelion the earth swings faster than at other periods (see Earth's Orbit Elliptical) , and that when in or near aphelion it swings more slowly, it will be seen that the distance around its orbit which it travels varies slightly from day to day. <* The farther it so travels in a given time, the farther it must rotate to bring any meridian under the sun twice in succession (from noon to next noon) and therefore the longer the day. The solar day accordingly varies in length; hence it is not perfectly adapted to commercial needs. To meet this objection, the average length of the solar days for a year (called by astronomers the mean solar day) has been found, and this is the exact, unvarying day as measured by the clock and as commonly meant by the word day in all civilized countries. This is the day of twenty-four hours. The use of the words average and mean as just used, when understood, convey the idea that some solar days are longer than the average and some are shorter; hence, compared with time as recorded by a good clock, time as indicated by the sun is sometimes slow and sometimes fast. At twelve by the clock it is not always noon by the 42 Globes and Maps in Elementary Schools sun. The difference between them is called the equation of time. These variations would not occur if the orbit of the earth were circular. Again referring to the analemma, observe that, at the point where the loops meet, a bar crosses the analemma, and on it are marked very short divisions to the right and to the left from the meridian which passes through the figure lengthwise. These divisions constitute a scale with which to compare the dates shown around the margin of the figure, and indicate the difference in minutes between sun time and clock time. To make the comparison, measure the distance from the central or dividing meridian to the inner margin of the figure opposite some date, and then measure off the same distance from the meridian on the minute scale or bar. This gives the difference in time between the sun and the clock on that date. On all the dates on one side of the meridian the sun is before the clock, on the dates on the other side the sun is after the clock. Note that, on four dates marked by the me- ridian, sun time and clock time are the same. The zodiac. 1 Viewed from the earth in its passage around the sun, the sun seems to pass in the same path, and in the same direction in the opposite heavens, making the complete circuit in one year. The path it follows is called the ecliptic. The ecliptic is marked as an oblique great circle on most globes, but the orbital plane repre- sented by the top of the circular wooden frame on a full mounted globe gives a clearer idea of it. Around the heavens astronomers have imagined a broad belt i6° wide (8° each side of the ecliptic), in the middle of which the iThis lesson explains familiar references to be found in every almanac, but it is of little practical value and may be omitted with- out much loss. The relations of the signs to various parts of the human body are merely fancied. Globes and Maps in Elementary Schools 43 sun appears to pass, and this was centuries ago divided into twelve equal parts of 30 each. This belt is called the zodiac. Each part was named after a conspicuous group of stars (constellation; Stella means star) which it included. Perhaps in order to make the location of par- ticular stars easier of description, men who had made a study of them charted them ages ago by covering the heavens with various imaginary outlines of animals, per- sons, and other objects in such a way as to bring the brightest stars in certain definite places upon them. For instance, one group appears in the outline of Orion, who in classic mythology was a famous hunter. Three bright, noticeable stars in nearly a straight line form his belt. The twelve constellations in the zodiac across which the sun seems to pass are as follows: Aries (meaning the ram, symbol, T), Taurus {the bull, symbol, tt ), Gemini {the twins, symbol, H), Cancer {the crab, symbol, @), Leo {the lion, symbol, Q.), Virgo {the maiden, symbol, TCP), Libra {the balance, symbol, — ), Scorpio {the scorpion, symbol, Til), Sagittarius {the archer, symbol, 9^), Capri- cornus {the goat, symbol, r6), Aquarius {the water-bearer, symbol, «*), and Pisces {the fishes, symbol, X). When the division of the zodiac was made over 2,000 years ago, the sun appeared to enter the constellation of Aries at the time of the spring equinox, about a month later to enter the constellation of Taurus, etc. The apparent position of the sun in the zodiac and therefore the time of year were indicated approximately by naming the constella- tion in which it appeared. If it was in Aries, for instance, the time was from about March 21 to April 21. Instead of the name of the constellation, the symbol or sign was often used, as tt for Taurus. Later, the twelve 44 Globes and Maps in Elementary Schools parts of the zodiac were called signs, and are so called to this day. For reasons which need not now be explained but which may be learned by consulting a good cyclopedia under the subject Precession of the Equinoxes, the signs as planned have every year gained on the constellations a little, or the constellations have fallen behind, so that now there is a difference or discrepancy of about 30 , the width of one entire division. The result is that each constellation now lies in the sign next in advance. For illustration, now, when the sun is said to be in the sign Taurus it is not in the constellation of Taurus as it was 2,000 years ago, but is in the constellation of Aries The orbital plane on a full mounted globe indicates the signs of the zodiac, and the corresponding time in months and days over which each extends. Planets. The earth is one of several large spheres or stars called planets which revolve around the sun at varying distances. They all revolve near the plane of the earth's orbit and in the same direction, and so are con- stantly changing their relative positions in the heavens as compared with the other stars. In the order of their distance from the sun, beginning with the nearest, they are Mercury, Venus, the Earth, Mars, a group of about 600 much smaller bodies called asteroids (aster means star; oid means like), Jupiter, Saturn, Uranus, and Neptune. Around some of these larger planets one or more smaller or secondary planets, often called satellites, revolve. All these planets and a few comets, together with the sun which holds them in place and around which they pass, comprise the Solar System. (Sol means sun.) All the other stars are immeasurably farther away, and as they are never seen to move they are called fixed stars. Globes and Maps in Elementary Schools 45 The moon. The moon is a sphere much smaller than the earth, which revolves as a satellite around the latter once in about twenty-eight days. If the earth be repre- sented by a globe twelve inches in diameter, a ball three inches in diameter would represent the relative size of the moon. It rotates around its axis, but so slowly that it turns only once while it is making one entire revolution. The result is that the same face is always toward the earth. Using the globe and a ball, show that when the moon is on the side opposite the sun, light from the sun is reflected to the earth by a full hemisphere of the moon, thus showing a full round face. This phase is called the full moon. We then see the day side of it. If the ball be painted white and this lesson be given by lamplight, the phases of the moon can be shown more clearly. When the moon is on the same side as the sun, no light is reflected from it to the earth. It then appears dark, as the night side of it is toward us. When it begins to show its day side we say the moon is new. Eclipses. When it occurs that the earth is exactly between the sun and the moon, the shadow of the earth passes across the moon, and we say there is an eclipse of the moon. The fact that this shadow is always round is one of the proofs that the earth is spherical. When the moon passes exactly between the sun and the earth, the body of the moon obscures the sun and we say there is an eclipse of the sun. (See Figs. 9 and 10.) Tides. The earth, the sun, the moon, and all other bodies attract each other. The attraction of the sun, for instance, is strong enough to hold the earth in its course, as has been shown, and the attraction of the earth is strong enough to hold the moon in its course. On the other hand, the attraction of the moon is so strong that it 46 47 i* § a -xa 8 ,*0 to 1 SO to 1 so so ~5 ;*-i so e o o s a "* ijfi 5 ^ "^ a 1 8 8 ■5 1 so •ft «xo 9 ^-~, to «6i s so o" .to e 1 1 -g i s i | "v § .to so "5 1 to so K 5 MB K i 1 ,8 .2 IS ,*3 2 to i 1 e g •