LIBRARY UNIVERSITY OF CALIFORNIA OF" Class OF S Mo. TEACHERS' MANUAL FOR Andrews' Lunar Tellurian BY HOWARD H. GROSS. Second Edition. PUBLISHED BY A. H. ANDREWS & Co., CHICAGO. 1882. Copyrighted by HOWARD H. GROSS, CHICAGO, iSSi. Introduction. To THE TEACHER : In the preparation of this Manual the writer has endeavored to treat the subjects presented, in a simple yet forcible manner, avoid- ing, as much as possible, technical terms. The illustrations given, ' outline the work that should be done in the class-room. The teacher should, and no doubt will supplement these illustrations in many ways, presenting the subjects treated, step by step, in a thorough and yet attractive manner. The value of demonstration is no longer doubted, and in those - schools where it is most used the best results follow. This is pre-eminently true in geographical and astronomical work. The Lunar Tellurian is designed to furnish the illustrations necessary to give the pupils a comprehensive understanding of the relation- ships of the earth, sun and moon. It is so simple in construction that the average teacher may use it to advantage after a few hours' study with the Manual. < The teacher will find it advantageous to now and then assign a topic to one of the pupils, and require him to furnish clear and forcible demonstrations by use of the apparatus. The teacher's attention is particularly called to the section in which Prof. E. Colbert, now scientific editor of the Chicago Tribune, and well known as a practical astronomer, treats the subject of Tides. His presentation is new, having reduced the abstract to the concrete. The author congratulates the readers upon being able to present an article from the pen of Prof. Colbert, and here acknowledges obligations to that estimable and scholarly gentleman. The writer acknowledges his obligations to M. MacVicar, Ph. D., of the Michigan State Normal School than whom there is no better authority on mathematical geography some of whose illustrations the writer has embodied in this work. CHICAGO, March i, iSSi. 111861 NDEX Introduction, j Andrews' Lunar Tellurian, Description, - 3 How to Adjust the Lunar Tellurian, - - 6 Preparatory Work, ... ^ General Definitions, - 8-16 Distribution of Light and Heat, - - 16-24 Days and Nights : Equal and Unequal, - 24-27 The Sun's Apparent Path, 27-28 Change of Season, 28-30 Twilights, 3 o- 33 The Sun's Declination, 34 To find the Latitude and Longitude oj Places, 35 Longitude and Time, - 37~39 To find the Difference of Longitude between Two Places, 39-4 1 To find the Time of Sunrise and the Length of Twilight, 41 The Sun, - 4243 The Earth, 44-45 The Moon, 45-46 The Moon's Motions, Phases, Etc., - 46-55 The Zodiac, Signs of, Etc., - 55~59 Eclipses, Solar and Lunar, - - - 59~68 Precession of the Equinoxes, - 6870 Equation of Time, 7~74 The Tides. By PROF. COLBERT, 74~79 Commendations of Andrews' Lunar Tellurian, 80 4 Andrews' Lunar Tellurian. A. The globe balL S. Arc of the sun's circumference, drawn upon the same scale as the globe. Extend the arc S until a circle is completed, and this circle shows the size of sun upon the same scale as the globe represents the earth. B. The circle of illu- mination, showing how far the sunlight extends. C. The twilight circle showing how far the twilight extends. D. The moon ball, showing the light and dark hemispheres of the moon. The gear- ing at F keeps the light hemisphere always toward the sun. E. Plate showing the inclinatian of the moon's orbit. G. A calen- dar index. L. Pointer showing the position of the sun's vertical ray. H. A longitudinal or time index, used to find time of sun- rise and sunset, length of days, nights and twilight. J. The ecliptic. K. The equator. LUNAR TELLURIAN MANUAL. To Adjust the Lunar Tellurian. To adjust the apparatus to agree with the calendar, move the arm IX until the calendar index G is opposite the 21st of June ; place the arm in which the south pole of the globe is fastened parallel with the arm IX, as shown in cut, or bring the calendar index to June 21st and place the center of the socket at the south pole op- posite the mark I on the semi-circular brace joining the ends of circle C. The pointer L should be parallel with the arm IX. Raise the moon ball until the gear wheels at F are disengaged, turn the cog-wheel to the right or left until the white side of the moon ball is toward the sun, drop the cogs into gear. The gearing will keep the bright side of the moon ball toward the arc S. The apparatus is now fully adjusted for use. For Geographical Study. (The Globe may be used for geographical purposes and is an excellent one for such use, having the Isothermal Lines indicated in blue and red. The ocean currents are also shown. When thus used, the teacher will remove the circles B C, also the curved standards supporting the same (after lifting off the globe ball along with the axis.) Replace the globe, detach the moon also, at F, by tipping the ball toward the globe. The sun arc S, may also be removed. All these changes take but a moment, giving an unobstructed view of the Globe.) LUNAR TELLURIAN MANUAL. Preparatory Work. The study of the method of adjusting and handling the LUNAR TELLURIAN GLOBE in illustrating and solving problems. Before using the globe in illustrations, the following points should be carefully studied. Each adjustment should be made familiar by actual practice. The teacher cannot be too particular on this point, as the power of any illustration depends largely upon the tact with which the piece of apparatus used is handled. The cut on the preceding page represents the globe with all the attachments in position. Let every part be removed and replaced and set in the positions indicated again and again, until everything required can be done with ease and rapidity. Be particular to notice the following suggestions : 1. The arc 6* represents the curvature of the surface of a ball which bears the same relation in size to the sun that the globe A bears to the earth. Hence by com- pleting the circle of which the arc 6 1 is a part, and com- paring it with a great circle on the globe, we have a correct representation of the relative size of the earth and sun. 2. The pointer L represents a line connecting the center of the earth and sun, hence, indicates the position of the only vertical ray of light or heat which comes from the sun to the earth. 3. The circle B is used to indicate the line which sep- arates light from darkness ; hence is called the " Circle of Illumination," or " Day and Night Circle." LUNAR TELLURIAN MANUAL. General Definitions. The following definitions should be made familiar before commencing the use of the globe. 1. A Point is that which has position without mag- nitude. 2. A Line is the path of a moving point. 3. A Straight Line is one which has the same di- rection throughout its entire length. 4. A Curved Line is one which changes its direc- tion at every point. 5. Parallel Lines are lines which have the same direction. 6. An Angle is the opening between two lines which meet in a common point called a vertex. There are three kinds of angles, thus : (1) (2) (3) (4) HORIZONTAL* Two Eight Angles, One Eight Angle. Obtuse Angle. Acute Angle. 7 When a line meets another line, making, as is shown (in 1), two equal angles, each angle is a Right Angle, and the lines are said to be perpendicular to each other. 8. An Obtuse Angle is an angle (as shown in 6 3), that is greater than a right angle. 9. An Acute Angle is an angle (as shown in 6 4), that is less than a right ang-le. LUNAR TELLURIAN MANUAL. 10. A Plane is a szirface traced by a straight line moving in the same direction. 11. A Circle is a surface enclosed by a curved line, %* every point of which is equally distant from a point within called the center. 1 2. A Circumference is the line that bounds the circle. In describing the lines on the sm-face of the globe, the word circle is used in place of circumference. When a circle proper is intended, the word "plane" is introduced. 13. A Degree is one of the 360 equal parts into which the circumference of a circle is supposed to be divided. Observe, the length of a degree varies with the size of the circle. 14. The Diameter of a circle is a straight line pass- ing through its center and terminating at both ends in the circumference. 15. The Radius of a circle is any straight line ex- tending from its center to the circumference. 16. A Sphere is a solid or volume bounded by a curved surface, such that all points in it are equally dis- tant from a point within called the center. io LUNAR TELLURIAN MANUAL. Observe the point e. in the cut in the margin, is the center of a sphere of which c b d is the lower half. 17. The Diameter of a sphere is a straight line passing through its center and termin- ating at both ends in the sur- face. In the cut, ab and cd are diameters. 18. The Radius of a sphere is a straight line drawn from the center to any point in the surface. In the cut, ce, fe, ae^ ge and de are radii. 19. A Great Circle of a sphere is one whose plane passes through the center of the sphere. Hence the planes of all great circles divide the sphere into two equal parts. Each part is called a Hemisphere. 20. A Small Circle of a sphere is one whose plane does not pass through the center of the sphere. Hence, the planes of all small circles on a sphere di- vide the sphere into two unequal parts. 21. The Axis of the Earth is that diameter on which it rotates once in twenty-four hours. 22. The Poles of the Earth are the two points on its surface at the extremities of its axis. 23. The North Pole is the Pole directed to the North Star. The South Pole is the opposite extrem- ity of the axis. LUNAR TELLURIAN MANUAL. 24. The Equator is a great circle midway between the poles whose plane is at right angles to the axis of the earth. 25. The Parallels of Latitude are small circles parallel to the Equator. 26. A Meridian is a semi-circle extending from Pole to Pole. 27. The Latitude of a place is its distance in de- grees north or south of the Equator. Places north of the Equator are said to be in North Latitude, and places south in South Latitude. 28. The Longitude of a place is its distance in de- grees east or west of a given meridian called the First or Prime Meridian. The meridian of the Royal Observatory at Greenwich, England, is commonly employed as the Prime Merid- ian. The French use the meridian of Paris ; the Ger- mans that of Ferro, one of the Canary Islands ; and Americans frequently use that of Washington. 29. The Tropic of Cancer is a parallel of latitude 23 1^ degrees north of the Equator. 30. The Tropic of Capricorn is a parallel of lati- tude 23 ^ degrees south of the Equator. 31. The Orbit of the Earth is the path in which it moves round the sun. Observe, the plane of the earths orbit is the plane in which the orbit is described. 12 LUNAR TELLURIAN MANUAL. 32. The Zones are broad belts or divisions of the earth's surface bounded by the Tropics and Polar Circles. These four lines divide the surface of the earth into five zones or belts known as the Torrid Zone, the two Tem- perate Zones, and the two Frigid Zones. The width of the Zones depends entirely upon the in- clination of the axis. The width of the Torrid Zone is double the inclination of the axis (23^ degrees), or 47 degrees. The width of the Frigid Zone is equal to the inclination. The Temperate Zones embrace whatever surface lies between the Tropics and Polar Circles (43 degrees). If the inclination of the axis were 30 degrees? as in the case of the planet Saturn, the Zones would be as follows : Torrid Zone, double the inclination, 30 or 60 Frigid Zones, each equal to the inclination, 30 or 60 Temp. Zones, each equal to the inclination, 30 or 60 Total degrees from pole to pole, 180 33. The Ecliptic is the sun's apparent yearly path through the fixed stars, or the earth' } s real path or orbit. 34. The Zodiac is a belt of the heavens 16 degrees wide, lying 8 degrees on each side of the Ecliptic, within which the sun, moon and planets are seen to move. This belt is divided into twelve equal parts called Signs of the Zodiac, These divisions, with their names, are represented on the base of the Lunar Tellurian. 35. The Equinoctial or Celestial Equator is a great circle of the Celestial Sphere directly over the terrestrial equator, and hence is in the same plane. LUNAR TELLURIAN MANUAL. 13 36. The Equinoctial Points or Equinoxes are the points where the Ecliptic crosses the Equinoctial. The point which the sun passes in March is called the Vernal Equinox, and that which he passes in September the Autumnal Equinox. 37. The Solstitial Points or Solstices are the two points where the sun is farthest from the Equinoctial. The point north of the Equinoctial is called the Sum- mer Solstice^ and the one south the Winter Solstice. 38. The Declination of a heavenly body is its dis- tance north or south from the Equinoctial. Declination corresponds to terrestrial latitude. 39. Perihelion is the point in the earth's orbit nearest to the sun. 40. Aphelion is the point in the earth's orbit far- thest from the sun. 41. Refraction in Astronomy is the change of di- rection which the rays of light undergo in passing through the atmosphere. 9 This may be illustrated to a class by placing on the blackboard a diagram ; thus, LUNAR TELLURIAN MANUAL. F E E F Let S represent the sun, D the earth, and F and E two strata of the atmosphere of which E is the more dense. Ask the pupil to observe, (a) That if a ray of light from 6" enter the stratum F at 3^ it will be bent toward the perpendicular 3b, and enter the stratum E at 2. The stratum E being more dense than the stratum F, it is again bent toward the perpendicular 2 & 9 and strikes the surface of the earth at 1. (3) That the atmosphere is not made up, as represented in the diagram, of separate strata of different densities, but becomes gradually more dense the nearer it is to the surface of the earth. Hence, the rays of light in passing through the atmosphere curve gradually toward a per- pendicular to the surface of the earth from the point where they enter the atmosphere. (c) That there Js no refraction when a ray of light strikes the atmosphere perpendicularly, as shown by the line lz, and that the more obliquely a ray enters, the greater the refraction, as shown by the line 1 3 S. Hencei LUNAR TELLURIAN MANUAL. 15 light coming from any heavenly body in our zenith, un- dergoes no refraction, and as a body moves from the zenith to the horizon, the refraction increases. (d) That since all objects are seen in the direction in which the light from them falls upon the retina of the eye, the sun S in the diagram is seen by an observer at 1 in the direction of SI. In consequence of this effect of refraction no heavenly body, unless in the zenith, is seen in its real position. In the case of the sun and moon, the amount of refrac- tion at the horizon is a little greater than their apparent diameters. Hence, in rising or setting, they appear above the horizon when they are actually below it. 42. The Radiation of heat with reference to the earth is the emission and diffusion of heat from its surface into the atmosphere. Ask the pupil to observe, (a) That during the day the surface of the earth is heated by the rays of the sun. (3) That when the sun sets the earth radiates its heat into the atmosphere ; hence, the change in the tempera- ture before the sun rises. In the summer season the earth's surface absorbs or takes in more heat from the sun during the long day than it radiates or gives out during the short night, the tem- perature must for this reason rise. When the sun leaves us and goes south our days shorten and nights lengthen, during which absorption diminishes, radiation increases, and the temperature is correspondingly lowered. The blacksmith puts the horseshoe into the forge that 16 LUNAR TELLURIAN MANUAL. it may absorb heat until it gets soft, so that he can easily shape it upon the anvil ; while working with it the shoe radiates heat, getting thereby more and more difficult to work. It must soon be replaced in the forge again to absorb the required quantity of heat to be easily arid economically wrought ; when the smith is through with the shoe he drops it into his tub of water that it may quickly radiate the heat and be ready to nail to the horse's hoof. Distribution of Light and Heat. To Illustrate the difference between the Sun's Ver- tical and Oblique Rays. Take two pieces of cardboard about a foot square. In the center of one of them cut a round hole about one inch in diameter ; hold this one up to the sun at a right angle to the rays, so that the light will pass through the opening ; place the other piece about a foot behind the first and parallel to it ; ask the pupils to observe that the sunlight passing through the inch opening falls upon the second piece vertical to it, and covers a like surface of one inch. This illustrates how the sunlight, falling verti- cally upon the earth, covers a surface equal to the volume of such light. Change the position of the back piece of cardboard slowly, so that it will not be parallel to the first, and ask the pupils to observe that while no more sunlight passes through the opening in the first cardboard than in the other illustration, yet that amount is spread over a greater surface on the second piece, owing entirely to the fact that it now falls obliquely ; whereas, in the first instance, it fell vertical to the surface of the cardboard. This illus- LUNAR TELLURIAN MANUAL. 17 trates how the sunlight, falling obliquely upon the earth's surface, covers a space greater in area than the volume of the light. Observe also, that the greater the obliquity ? the greater the space covered. Remove the second piece of cardboard, and put the globe in its place in such a manner that the sunlight ad- mitted through the first cardboard shall fall vertical to the surface upon the equator. Observe that the area of light on the surface of the globe is about equal to the area of the hole admitting the light. Raise the cardboard so that the sunlight will fall upon the 40th parallel of north latitude, and observe that while no more sunlight is ad- mitted, it covers a much greater area, and must be less intense there than on the equator where the sun was vertical. In the same manner place the sunlight on the 60th parallel, and observe the greater obliquity and the greater area covered. Call special attention to the fact that the curvature of the globe is the only cause of the rays in the higher latitude being more oblique than they are in the lower latitudes. Observe, that what is true of a small globe and a por- tion of sunlight, is true of our earth as a sphere, and the greater volume of sunlight,* Thus we find i. That the nearer the vertical sun, the more intense the light and heat ; and the farther from the vertical sun, the less intense the light and heat. The cause of the heat of summer and cold of winter is not more due to the angle at which the rays of sun- light strike us, than to the relative lengths of day and night at these seasons. In midsummer we are about 15 i8 LUNAR TELLURIAN MANUAL. hours in sunlight, wherein we are warming, and about 9 hours are turned away in darkness to cool, while in midwinter we have about 9 hours of sunlight and 15 hours of darkness. As we depend upon sunlight for heat, it follows that the temperature must rise in summer and fall in winter, owing to the longer and shorter periods of sunshine at these respective seasons. 2. That only one-half of the earth's surface can at any time, be exposed to the sun's light and heat. This half is called the Illuminated Hemisphere. Rotate the globe on its axis from west to east 10 de- grees, and ask the pupils to observe, in case the earth moves in like manner : (a) That a distribution of light and heat will have taken place. (b) That the vertical rays of the sun will have been carried westward 10 degrees upon the earth's surface, owing to this rotation to the east ; or, the sun's vertical ray will have been distributed east and west 10 degrees. (c) That the boundary of sun's light and heat will have been carried westward from 90 degrees west longitude to 100 degrees, and that all places situated between these *NOTL. If convenient, place a convex lens over the aperture in the cardboard ; place the second board behind, as directed in the first instance, and at such a distance as necessary to make the converging rays cover the least possible surface ; hold the sunlight upon the same point for a few moments ; and if the lens is a good one, combustion will ensue at the point of contact, thus illustrat- ing the intense heat produced by reducing the space covered by a given portion of sunlight. The intensity of solar heat is inversely proportional to the space covered by a given volume. LUNAR TELLURIAN MANUAL. 19 meridians will have been by this distribution brought into the illuminated hemisphere, while those places situ- ated between the 90th and 80th meridians east longitude will have been carried out of it. (d) That the Day and Night Circle is parallel with the meridians as they pass under it. Rotate the globe once upon its axis from west to east, and ask the pupils to observe : (a) That by reason of this rotation the sun has crossed every meridian and returned to the place of starting. (b) That every meridian has passed through the illu- minated and the dark hemispheres. Hence, one com- plete distribution of light and heat east and ivest has taken place, being produced by the rotation of the earth upon its axis. As the earth turns once upon its axis daily, there must occur a daily distribution oj~ light and Tieat east and west upon the eart/i's surface. (c) That when the sun is vertical to the equator, as on March 20th and September 23rd, the light and heat of the sun is equally distributed in the north and south hemispheres. To Illustrate the Distribution of Light and Heat on March 2Oth. To produce a distribution of the sun's light and heat upon the earth's surface, the earth or sun must change their position in respect to the other. This necessitates a movement, and without a movement no distribution can take place. It is very necessary that the pupils get a clear concep- tion of this subject and master it, as upon the distribution 20 LUNAR TELLURIAN MANUAL. of light and heat depend the succession of day and night, the twilights, change of seasons, and, in fact, our very existence. Bring the calendar index to the 20th of March ; rotate the globe upon its axis until the sun is vertical to the prime meridian, and ask the pupils to observe : (a) That the sun is vertical to the equator. (b) That the sun's light and heat extends north and south from pole to pole, as shown by the Day and Night Circle B. (c) That the sun's light and heat extends east and 'west of the prime meridian 90 degrees, as shown by the Day and Night Circle B. To Illustrate the Distribution of Light and Heat on the 21st of June. Bring the calendar index to the 21st of June, and ask the pupils to observe : (a) That the sun is vertical to the Tropic of Cancer, 23 y z degrees north of the equator. (b) That the Illuminated Hemisphere now extends 23 y^ degrees beyond the north pole, and that it fails to reach the south pole by the same number of degrees. (c] That the place upon the earth's surface where the vertical ray falls, is the center of the Illuminated Hemi- sphere, and that any change in position of this point pro- duces a like change in the Illuminated, and an opposite change in the Dark Hemispheres. (d] That on June 21st the light and heat of the sun is unequally distributed in the north and south hemispheres ; LUNAR TELLURIAN MANUAL. 21 that the Illuminated Hemisphere predominates north of the equator, and the Dark Hemisphere predominates south of it. Rotate the globe upon its axis, and ask the pupils to observe : (a) That the vertical sun traces the Tropic of Cancer. (3) That as the earth rotates upon its axis, in this man- ner, all places within the Arctic circle will remain in sunlight, while corresponding places within the Antarctic will remain without sunlight. (c) That from the 20th of March to the 21st of June, the vertical sun has been carried north 23*^ degrees, or that a north and south distribution to the extent of 23 ^ degrees has taken place. To Illustrate the Distribution of Light and Heat on the 23d of September. Bring the calendar index to the 23d of September ; this illustrates the relationship that exists between the earth and sun on that day. Ask the pupils to observe : (a) That the vertical sun has, from the 21st of June to the 23d of September, been carried south from the Tropic of Cancer to the equator ; and that the Illumin- ated Hemisphere has been correspondingly changed, so that on September 23d, the sun's light and heat is again equally distributed in the north and south hemispheresi and extending from pole to pole, as on March 20th. (b) That whatever distribution was shown, or what- ever observations could be made on March 20th, are again reproduced on September 23d. 22 LUNAR TELLURIAN MANUAL. To Illustrate the Distribution of Light and Heat on December 22d. Bring the calendar index to the 22d of December, and ask the pupils to observe : (a) That the sun is vertical 23^ degrees south of the equator. (b) That the Illuminated Hemisphere now extends 23 y 2 degrees beyond the south pole, and that it fails to reach the north pole by the same number of degrees. (c) That, on December 22d, the light and heat of the sun is again unequally distributed in the north and south hemispheres, and that the Illuminated Hemisphere pre- dominates south of the equator, and the Dark Hemi- sphere predominates north of it. Rotate the globe upon its axis, and ask the pupils to observe : (a) That the vertical sun traces the Tropic of Capri- corn. (b) That as the earth rotates upon its axis in this manner, all places within the Antarctic circle remain in sunlight, while corresponding places within the Arctic circle will remain without sunlight. (c) That from the 23d of September to the 22d of December the vertical sun has been carried south 23^ degrees, or that a north and south distribution has taken place. Bring the calendar index slowly to starting point (March 20th,) and observe : That the vertical sun is carried from the Tropic of Capricorn to the equator, the place of beginning; and that a north and south distribu- LUNAR TELLURIAN MANUAL. 23 tion of the sun's light and heat has taken place from the equator to both tropics and return, and that the time necessary to do this is one year ; and, as the vertical ray is distributed, so must all other rays that touch the earths surface be affected. Thus we see that there is a double distribution : east and west daily, and north and south annually. The Causes of the Existing Distribution of Light and Seat. 1. The daily distribution east and west is caused by the daily rotation of the earth on its axis. 2. The annual distribution north and south is caused : (a) By the revolution of the earth in its orbit around the sun. If the earth remained fixed in its orbit, and revolved upon its axis, but one distribution could take place the daily. (3) By the inclination of the earth's axis. Notice that on the 20th of March the axis is inclined 23^ degrees, but that the inclination is neither to nor from the sun, and that the sun is then vertical to the equator. Notice that on the 21st of June the north pole is inclined to the sun the full inclination of 23^ degrees, and for this reason the sun is vertical the same number of degrees north of the equator. On December 22d, the north pole is inclined from the sun the full inclination, this bring- ing Capricorn under the sun. Erect the axis by sup- porting the globe on the other socket, call the pupil's attention to the fact that the equator and the ecliptic now lie in the same plane. Revolve the earth around the sun and observe that the vertical ray falls constantly 24 LUNAR TELLURIAN MANUAL. upon the equator ; without an inclination no annual distribution of light and heat could take place. (c) By the parallelism of the eartJi's axis. The axis is said to be parallel, because it points continually to the same part of the heavens I thus, the north pole points constantly towards the North Star, while the earth re- volves around the sun. Revolve the globe around the arc S and observe that the axis points constantly in the same direction. This is true of the earth and all the planets as they revolve in their several orbits. This is termed the parallelism of the axis. Equal Days and Nights. 1. Bring the calendar index to the 20th of March, and ask the pupils to observe : (a) That the Day and Night Circle B divides the earth into two divisions day and Night : that all places on the side of this circle next to the sun have day, while those places on the opposite side have night. (6) That at this season of the year the sun is vertical to the equator, and the Day and Night Circle is parallel to opposite meridians. *(c) That in this position the Day and Night Circle divides every parallel of latitude, from pole to pole, into tivo equal parts. Rotate the globe slowly upon its axis, and ask the pupils to observe : (a) That all places upon a given meridian enter the sunlight at the same moment. (&) That one-half a rotation on the axis carries these TELLURIAN MANUAL. 25 places through the Illuminated Hemisphere, where they pass beyond the Day and Night Circle, when the day ends and night begins. (c) That one-half a rotation carries these places from sunset to sunrise. Thus we see that on March 20th, the days and nights must be equal all over the earth's surface. Bring the calendar index to the 23d of September, and ask the pupils to notice that the same condition that ex- isted on March 20th, again exists, with the same result equal days and nights. Unequal Days and Nights. Bring the calendar index to the 21st of June, and ask the pupils to observe : (a) That the sun is vertical 23 ^ degrees north of the equator, and that the sunlight extends 23^ degrees beyond the north pole, and fails to reach the south pole by the same number of degrees. (b) That the Day and Night Circle no longer divides the parallels of latitude into equal parts, but into two unequal parts ; and that north of the equator the greater part of every parallel is in the sunlight, and the lesser part in darkness ; while south of the equator the lesser part is in sunlight, and the greater part in darkness. (c) That the entire parallels within 23 y z degrees of the north pole are now in constant day, while those within the same distance of the south pole are in con- tinual night. Rotate the globe on its axis, and ask the pupils to observe : 26 LUNAR TELLURIAN MANUAL. (a) That no sunlight or day reaches that portion of the earth's surface within the Antarctic circle, although the earth may revolve upon its axis. () That the entire area of the earth's surface within the Arctic circle, is not carried out of the sunlight by the rotation of the earth upon its axis. (c) That the Day and Night Circle cuts the equator at opposite points, and that there the days and nights are equal. (d) That, as you proceed north from the equator to the Arctic circle, the days increase in length gradually from 12 hours at the equator, to 24 hours within the Arc- tic Circle. (e) That, as you proceed south from the equator to the Antarctic circle, the days decrease in length gradually, from 12 hours at the equator, to hours within the Ant- arctic Circle. Bring the calendar index to the 22cl of December, and ask the pupils to observe : that what was true of the northern in June, is now true of the southern hemi- sphere in December. Thus it is evident 1. That when the sun is upon the equator, the days and nights are everywhere equal. 2. That when the vertical sun is one or more degrees north or south of the equator, continual day must exist around the pole nearer the sun, and continual night must exist around the pole farther from the sun ; the extent of this area of continual day and night depending upon the distance of the vertical sun north or South of the equator. LUNAR TELLURIAN MANUAL. 27 3. That the days and nights at the equator must al- ways be equal. 4. That as you depart from the equator, the variation in the length of day and night increases, and as you ap- proach the equator the variation becomes less : the max- imum variation being in the polar, and the minimum in the equatorial regions. 5. That the length of any day upon any parallel of north latitude, is equal to the night following on the cor- responding parallel of south latitude. NOTE. In this work we regard day as the time when the sun is present, and night as the time when he '^absent. Night does not necessarily mean darkness. Night begins at sunset and ends at sunrise. The Sun's Apparent Path. Bring the calendar* index to the 21st of June, rotate the globe on its axis until the Ecliptic marked upon the globe is brought under the vertical Sun. Move very slowly the calendar index through the succeeding months until it again comes to the 21st of June, and ask the pupils to notice that the vertical sun traces the ecliptic and if the earth had no daily rotation on its axis, that the ecliptic would mark the true path of the Sun upon the earth. Rotate the earth upon its axis and ask the pupils- to observe that the Sun traces the Tropic of Cancer, and that if the sun should leave behind it a thread of light> that thread would lie upon the tropic. Move the calen- dar index to the 22d of June, and rotate the globe upon its axis, and notice that the sun traces a line parallel to the Tropic of Cancer, but about * of a degree south of it. In the same manner proceed with several days in 28 LUNAR TELLURIAN MANUAL. succession and observe that by reason of the rotation of the earth upon its axis and the movement forward of the earth in its orbit at the same time, the path of the vertical sun will be a continuous line running from east to west, and winding south from Cancer to Capricorn, and returning during the year, much as a thread is wound upon a spool. Change of Seasons. To produce what is called a change of season at any place, more solar heat must fall upon that place during one part of the year than at another. Within the tropics the amount of heat received from the sun is nearly uni- form throughout the year, so that very little change of season takes place ; the greatest changes occurring in the higher latitudes. Bring the calendar index to the 20th of March and ask the pupils to observe : (a) That the light and heat of the sun are equally dis- tributed in the north and south Hemispheres. (6) That if the earth remained fixed in its orbit and was rotated upon its axis, there could be no change of seasons. Bring the calendar index to the 21st of June and ask the pupils to observe : (a) That the sun is now vertical to the tropic of can- cer, and that the sun's light and heat is unequally dis- tributed in the north and south hemispheres, the north hemisphere having the greater and the south hemisphere the lesser amount. LUNAR TELLURIAN MANUAL. 29 (b) That owing to this inequality 4jie north hemisphere is having its greatest amount of light and heat, its warmest season or Summer, and that the south hemi- sphere is having its coldest season or Winter. Bring the calendar index to the 23d of September and ask the pupils to observe that the light and heat is again equally distributed north and south of the equator as in March 20th. Bring the calendar index to the 22d of December and ask the pupils to observe that the sun is vertical to the tropic of Capricorn, the sun's light and heat being again uneqally distributed in the north and south hemispheres, the south having the greater and the north the lesser amount ; and that at this time in the year the south hemisphere is having the warmest season or Summer, while in the north it is in the coldest or Winter season. Bring the calendar index to the 20th of March, and observe that the sun is brought to the equator going north and that as it crosses, Spring begins in the north and Autumn or Fall begins in the south hemisphere. The Causes that produce the Change of Seasons. The change of seasons is produced by, (a) The revolution of the earth in its orbit around the sun. (b) The inclination of the earth's axis to the plane of the orbit. (c) The parallelism or fixed position of the earth's axis. 30 LUNAR TELLURIAN MANUAL. (d) The rotation of the earth upon its axis. To illustrate that the rotation of the earth upon its axis is one of the causes that produce the changes of sea- sons as they now exist : bring the calendar index to the 20th of March, mark the point upon the equator where the sun is vertical at that time ; now move the calendar index slowly through the succeeding months of the year until it is again vertical to the same point. Call the pupil's attention to the fact that if the earth did not rotate upon its axis the sun would require one year to cross all the meridians once, and that in this case it would cross them from west to east instead of from east to west; that the sun would in that event rise in the ivest and set in the east, and our day and year would be of the same length ; and, that if this were true, the side of the earth towards the sun would be parched by the ex- treme heat, while the opposite side would become frozen and lifeless. So, if the earth did not rotate on her axis, no changes of seasons as they now exist could take place, nor in fact could animal or vegetable life as now con- stituted endure the extremes of heat and cold to which they would be subjected. Twilights. To show how the sun after going below the horizon continues to give reflected light, and hence, produces twilight. * The molecules of which the atmosphere is composed, reflect the light they receive from the sun, and by the light so reflected, objects .are seen in the absence of direct sunlight The atmosphere is capable of thus reflecting LUNAR TELLURIAN MANUAL. 31 light a mean distance of 18 degrees of a great circle. Call the pupils' attention to the fact that the sun gives direct light from the point where he is vertical to the Day and Night Circle B, and that the indirect or reflected light extends to thfc circle C, and that file space between these circles is called the Twilight Belt. Hence the earth's surface as regards light is divided into three sec- tions : 1. A hemisphere of direct light. 2. A belt 18 degrees wide of reflected light or twilight. 3. The re- maining portion without light. To Illustrate the Twilight on the 20th of March. Bring the calendar index to the 20th of March. Call the pupil's attention to the fact that there are two twi- lights, Evening and Morning ; that the evening twilight deepens into darkness, while the morning twilight bright- ens into sunshine. Rotate the globe upon its axis and ask the pupils to observe : that places upon the earth's surface must cross the twilight belt twice in every 24 hours. Rotate the globe slowly upon its axis and ask the pupils to observe : that all places upon the same meridian from pole to pole pass into evening twilight at the same instant, but that those places located near the equator pass out of twilight first, and that the higher the latitude the longer the twilight continues. This varia- tion is due : 1st. To the fact that at the equator the earth rotates faster than it does near the poles, for the same reason that the outer part of a wagon wheel turns faster when the wagon is in motion, than the hub. 2d. This variation is partially due to the fact that places near the equator are carried across the twilight 32 LUNAR TELLURIAN MANUAL. belt in a straight line, and at right angles to it : while near the poles places enter the twilight at right angles with the first circle and cross the belt not in a direct line, but travel on an arc of a circle passing obliquely across the second circle. From this we see that places in the higher latitudes must travel farther to cross the twilight belt, and at the same time, much slower than those places situated near the equator. Locate upon the map of the globe the place where you are situated, rotate the globe upon its axis and ask the pupils to note carefully the manner this place is carried across the twilight belt. This illustrates the twi- lights on the 20th of March, for that place. To Illustrate the Twilights on the 21st of June. Bring the calendar index to the 21st of June and ask the pupils to observe : (a) That the twilight belt no longer conforms to the meridians, and that no two places upon the same meri- dian enter the evening or emerge from the morning twilight at the same moment. (&) Those places that in March cross the twilight belt at right angles to it, now cross it obliquely, so that the twilights for these places must be longer in June than in March. (c) That the obliquity is least at the equator, and in- creasing as the latitude increases. Locate upon the map of the globe the place where you are located, rotate the globe upon its axis and ask TM UNIVERSITY OF SSL LUNAR TELLURIAN MANUAL. 33 the pupils to observe that this place is carried across the twilight belt more obliquely than in March, and that the twilight must be of longer duration. To Illustrate the Twilight on the 23d of September. Bring the calendar index to the 23d of September, ex- amine the twilight in the same manner as upon the 20th of March, and ask the pupils to notice that all the facts are the same as were observed at that date. To Illustrate the twilight on the 22d of December. Bring the calendar index to the 22d of December, and ask the pupils to notice that places upon the earth's sur- face are carried across the twilight belt obiquely substan- tially as in June. Compare the twilights of any place* at different dates by use of the globe, taking the 21st of June as the basis of comparison, and repeat the comparison until the pu- pils see clearly, (a) That on the 21st of June the given place crosses the Twilight Belt more obliquely than on either of the other dates, and hence the longest twilight. (b) That on the 20th of March and 23d of September, the path of the given place across the Twilight Belt is the same, and less oblique than at either of the other dates, and hence the shortest twilight. (c) That on the 22d of December the given place crosses the Twilight Belt less obliquely than on the 21st *The author would suggest that the place selected be in north latitude 40 to 50 degrees. 34 LUNAR TELLURIAN MANUAL. of June, and more obliquely than on the 20th of. March and 23d of September. Hence, a mean twilight between the other two. 3d. Now ask the pupils to notice that on the 22d of December the sun is vertical to south latitude 23^, and on the 21st of June, north latitude 23^. Consequently the sun sustains the same relation in every particular to the Southern Hemisphere at the former date, that it does at the latter date to the Northern. Hence, all the facts observed regarding the twilight on the 21st of June in northern latitudes apply on the 22d of December to cor- responding southern latitudes. Hence, all the facts ob- served on the 22d of December in northern latitudes may be found on the 21st of June in the southern latitudes. Sun's Declination. The Sun's , Declination is his distance north or south of the equator (as indicated by the vertical ray). When the sun is north of the equator he is said to have a north- ern declination ; when south of the equator he is said to have a southern declination. The greatest northern declination (23 1^ degrees) oc- curs on the 21st of June, and the greatest southern de- clination (23 y z degrees) occurs December 22d. At the time of the equinoxes (March 20 and September 23d), the sun has no declination. To Find the Sun's Declination for any Day. Bring the calendar index to the given day, rotate the globe upon its axis until the meridian having the degrees upon it is brought under the pointer L. Extend the LUNAR TELLURIAN MANUAL. 35 pointer L to the globe. The degree of latitude under the pointer is the required Declination. To Find the Longitude of any Place, Rotate the globe upon its axis until the given place is under the pointer H, the degree on the equator at the end of the pointer H is the longitude required. The longitude is east or west according as the place is east or west of the Prime Meridian. EXAMPLES. 1. What is the longitude of New York ? 2. What is the longitude of Calcutta ? 3. What is the longitude of Quito ? 4. What is the longitude of St. Petersburg ? 5. What is the longitude of Honolulu ? To Find the Latitude of any Place. Rotate the globe upon its axis until the given place is brought under the pointer H, above the place on the pointer read the degree of latitude required ; or, bring the given place under the edge of circle B, mark the circle directly over the given place, rotate the globe until the meridian having the degrees marked upon it is brought under the circle. Under the point marked, read upon the meridian the degree of latitude required. If the place is north of the equator it is north latitude, if south of it, south latitude. EXAMPLES. 1. What is the latitude of New York ? ;2. What is the latitude of Calcutta ? 3. What is the latitude of Quito ? 4. What is the latitude of St. Petersburg ? 5. What is the latitude of Honolulu ? 6. What is the latitude of Santiago ? LUNAR TELLURIAN MANUAL. CUT No. 2. Remove the day and night circle, as in the above cut. As now seen, the Lunar Tellurian should be used to explain the phases of the moon, eclipses, equation of time, precession of equinoxes, etc. 36 LUNAR TELLURIAN MANUAL. 37 Longitude and Time. Longitude is distance, measured however in degrees, minutes and seconds, east or west of a given meridian called the Prime Meridian. Observe that the degrees are marked upon the globe at the equator, east and west from the meridian of Greenwich the Prime Meridian. On page (9) we learned that every circle is divided into 360 equal parts called degrees, every degree is sub- divided into 60 equal parts called minutes, and every minute is subdivided into 60 equal parts called seconds. The earth in its relation to the sun turns once on its axis (360 degrees) every 24 hours, and must turn as many degrees every hour as 24 is contained times in 360 or 15 degrees. Since it turns 15 degree* in one hour, to turn one degree it will require 1-15 of an hour or 4 minutes of time. Rotate the globe from west to east until the pointer L is over the prime meridian ; noon now takes place upon that meridian from pole to pole. Observe that all places east of this meridian have passed the sun and that their noon has passed, while those places to the west have not yet been brought to the sun, and their noon will not yet have taken place. EXAMPLE 1. When it is noon (12 o'clock) at Greenwich, what is the time in Hamburg, say 10 degrees east of Greenwich ? Hamburg being east of Greenwich the time is later by the time required by the earth to turn 10 degrees. Since the earth turns one degree in 4 minutes, to turn 10 de- grees will require 10 times 4 minutes or 40 minutes. The difference in time is therefore 40 minutes, and since it is 12 o'clock at Greenwich, it is 40 minutes after 12 at Hamburg, or 20 minutes to 1 p. M. 38 LUNAR TELLURIAN MANUAL. EXAMPLE 2. When it is noon at Greenwich what is the time at Rio Janeiro, Brazil, 52 degrees west ? Rio Janeiro being ivest the time is earlier by the time required by the earth to turn 52 degrees. Since the earth turns 1 degree in 4 minutes, to turn 52 degrees will require 52 times 4 minutes, or 208 minutes. Reduced = 3 hours 28 minutes ; the time before noon at Rio Janeiro 12 o'clock noon less 3 h. 28 min. = 8 o'clock 32 min. A. M. the time at Rio Janeiro. EXAMPLE 3. When it is 11 o'clock A. M. at Hamburg what is the time at Charleston, S. C., 80 degrees west ? Charleston being west the time is earlier. Charleston is 80 degrees west of Greenwich and Hamburg 10 degrees east, the distance between Charleston and Hamburg is therefore 80 degrees + 10 degrees = 90 degrees ; 1 deg. = 4 min. 90 deg. = 90 X 4 = 360 minutes, reduced, = 6 hours. 11 o'clock A. M., less 6 hrs. = 5 o'clock A. M. EXAMPLE 4. When it is 10 o'clock A. M., at Constantinople, 28 de- grees east, what is the time in Hong Kong, 112 degrees east ? Hong Kong being 112 degrees east and Constan- tinople being 28 degrees east, the distance between them is 112 deg. less 28 deg. = 84 deg.; 1 deg. = 4 min.; 84 deg. = 84 X 4 = 336 min.; reduced = 5 hrs. 36 min. difference in time. Hong Kong being east, the time there is later than 10 o'clock A. M. by 5 hrs. 36 min. ; 10 hrs. -f- 5 hrs. 36 min. = 15 hrs. 36 min. or as commonly read, 3 hrs. 36 min. p. M. LUNAR TELLURIAN MANUAL. 39 EXAMPLE 5. When it is 11. 30 A. M. at San Francisco, 122 cleg, west, what is the time at Melbourne, Australia, 143 cleg, east ? Ans. 5 hrs. 10 min. A. M. Observe that the greatest longitude a place can have is 180 deg., that is, half way around the earth from the prime meridian. If a person start at the prime meridian and go west he will be in west longitude until he reaches 180 degrees, when his longitude is either east or west. If he proceed on his course ten degrees, his longitude is 180 degrees east, less 10 degrees, or 170 East. If a companion had gone 10 degrees east his longitude would be 180 degrees west less 10 degrees, or 170 West ; the men are manifestly 20 degrees apart. To Find the Difference in Longitude Between Two Places. 1. If both places are in the same longitude either east or west, deduct the less from the greater and the result is their difference. 2. If one place is east and the other west, the sum of their longitudes is the difference, provided the sum does not exceed 180 degrees. 3. If one place is east and the other west, and the sum of their longitudes exceeds 180 degrees, deduct the amount from 360 degrees, and the remainder is the differ- ence of longitude sought. Suppose James and Howard leave the prime meridian, James going west and Howard going east ; when each has traveled 80 degrees they are 160 degrees apart, which is their difference in longitude, Howard being east of James. Let each proceed 10 degrees farther and 40 LUNAR TELLURIAN MANUAL. they are 180 degrees apart, on opposite meridians, How- ard being either east or 'west of James. Let them con- tinue in their course 10 degrees ; James is then 100 degrees west and Howard 100 degrees east. Together they have traveled 200 degrees, and as 360 degrees are all there is to travel, 360 200 = 160, the number of degrees between them, Howard being now 160 degrees 'west of James. Let us presume they started on their journey at noon, and that they carried accurate time pieces ; when they had traveled 15 degrees James would find his watch an hour too fast, and to correct it he must turn it back, while Howard's watch is found to be an hour too slow and must be set ahead. To keep the watches right, these changes must be made constantly, James turning his watch back 4 minutes for every degree traveled, and Howard setting his ahead in the same proportion. When each has traveled 80 degrees as above, and it is noon at the prime meridian, James' watch shows 6 hrs. 40 min. A. M. (80 X 4 = 320 min. = 5 hrs. 20 min. subtracted from 12 noon = 6 hrs. 40 min. A. M.) and Howard's watch shows 5 hrs. 20 min. p. M. When each has trav- eled 90 degrees, James has 6 o'clock A. M. and Howard 6 o'clock P. M. when it is noon at the prime meridian. When each has traveled 179 degrees, James' watch shows 4 minutes A. M., and Howard's shows 11 hrs. 56 min. p. M. When they meet at 180 degrees their watches show the same hour, 12, midnight. James has gained 12 hours by setting his watch back, while Howard has lost 12 hours by setting his ahead. Though both watches indicate the same hour there is really a day's difference in their time. Were they quick-witted Hibernians, we might readily LUNAR TELLURIAN MANUAL. 41 imagine them addressing each other somewhat like this: Hello ! faix, its to-day wid me, but it's yesterday with you. It's nayther, sir, the other replies. It's to-day wid me and to-morrow wid you. To Find the Time of Sunrise for any Place or any Day in the Year. Arrange the globe as shown in Cut No. 1. Bring the calendar index to the given day, rotate the globe upon its axis until the given place is under the western edge of the day and night circle ; place the time index H opposite zero on the equator ; tighten the screw to hold it firmly in position. Turn the globe upon its axis from west to east, until place mentioned is opposite the pointer L ; note on the equator the number of degrees of longi- tude that has passed under the pointer, reduce the longi- tude to time (as directed in Longitude and Time, page 37). The result is the time from sunrise to noon, which subtracted from 12 o'clock noon, gives the hour of sun- rise. EXAMPLES. 1. What is the time of sunrise at Chicago, May 1 ? 2. What is the time of sunrise at New Orleans, June 30, 1881. 3. What is the time of sunrise at Melbourne, Jan- uary 10 ? To Find the Duration of Twilight for any Place on any Day in the Year. Arrange the globe as above. Bring the calendar in- dex to the given day, and the given place to the begin- ning of twilight. Set the index H opposite zero on the equator ; rotate the globe upon its axis until the given 42 LUNAR TELLURIAN MANUAL. t place is carried across the twilight belt ; note the num- ber of degrees on the equator the globe has turned, which reduce to time, and the result is the duration of twilight required. "EXAMPLES. 1. What is the length of twilight at San Francisco,, August 1 ? 2. What is the length of twilight at Berlin, June 21 ? The Sun. The sun is the center of our solar system, and around him all the planets revolve and from him receive their light and heat. In matter he is 750 times greater than all the planets combined. As all bodies attract each other and in proportion to the amount of matter they contain, so the sun's attraction must be 750 times greater than the combined attraction of all the planets, and were they all to unite they could not move him his own diameter from the center of gravity of our solar system. So we may justly regard the sun as the center of gravity. The attraction of the sun is so much greater than the earth's, that a boy weighing 75 Ibs. on the earth would weigh over a ton if placed upon the sun. The ancients thought the sun to be an immense globe of iron heated to a white heat. While this is not liter- ally true, it shows they had a better idea of the sun than of the earth, which they thought to \>ejlat. The apparent diameter of the sun is about y z a de- gree rather more than less. When viewed through a powerful telescope his surface presents a mottled appear- ance, which Professor Newcomb likens to a dish of rice soup with the rice grains floating upon the surface. LUNAR TELLURIAN MANUAL. 43, The sun seems to be surrounded by a very rare, light atmosphere, principally hydrogen heated to a glow, in which fleecy cloucls seem to float ; these clouds serve to cut off from us some of the fierce light and heat of the sun, and were it not for these, astronomers tell us his light and neat would be intolerable. The prevailing opinion of the best authorities is, that the sun proper is composed of condensed gases under great pressure, and heated to a temperature many times greater than furnace heat. The solar spectrum shows the presence of hydrogen, iron, magnesium, sodium and other elements in the sun ;, but of what the sun is composed we know very little. His extreme brightness renders observations very diffi- cult. If the sun were placed at the distance of the nearest fixed star he would appear no larger than one of the smaller stars. The Sun has three motions, as follows : 1. A rotation upon his axis once in 25 days, 9^ hours. 2. A revolution around the center of gravity. This movement is very slight. 3. A revolution around some distant and unknown center, carrying with him the entire solar system at a rate of 20,000 miles an hour, and traveling in an orbit so great that to make one complete revolution requires about eighteen million years! This is perhaps the most astounding of all astronomical movements, and the question " Whither are we going ?" may well be asked I 44 LUNAR TELLURIAN MANUAL. The Earth. The Earth is one of the eight principal planets. She ranks fifth in size, and third in her distance from the sun, Her distance varies between 91 and 94 million miles. She has at least eight distinct motions, but some of them it is not our province to consider in this work. Among the simpler and better understood of the number are : 1. Rotation upon her axis every 24 hours. 2. Revolution around the sun annually in an Elliptical orbit. 3. Revolution of the equator around the pole of the Ecliptic. (See Precession of the Equinoxes.) The Earth's surface is divided into solid and liquid, there being about 3-10 of the former and 7-10 of the latter. The solid we call land and the liquid water. The crust and liquid covering of the earth as compared with her size is very thin, probably not a hundred miles thick, and if shown upon the globe the crust would be reduced to the thickness of thin cardboard ! This crust is sup- posed to float on the molten fiery interior of the earth. Among the proofs that the interior of the earth is a sea ot fire, are the following : 1. As we go down into the solid crust of the earth the temperature rises at nearly the uniform rate of 1 degree for every 50 feet we descend. At a distance of less than 2 miles, water would boil; at a depth of 10 miles, the crust would be red-hot. Below the surface, 90 to 100 miles, the temperature would be sufficient to melt any substance known to man. LUNAR TELLURIAN MANUAL. 45 2. In various parts of the earth's surface we find springs of hot water boiling up out of the earth's crust, and we know of no way the water could be heated except by the internal fires of the earth. 3. Volcanoes, that seem to act as safety valves, through which the Furies of the pent up fires find relief in send- ing forth fire, gases and lava. The latter is composed of well-known substances, such as rock and minerals melted to a liquid form. 4. The form of the earth flattened at the poles and bulged out at the equator, shows that the earth in her childhood (if we may be allowed the term), must have been in a soft, pliable state, in which case the earth would necessarily assume the form she now has. From what we know of the interior of the earth it could not have been in this soft plastic state except by the action of heat. Geological formations show evidences of great heat at some former period of the earth's existence. The Moon. The Moon's Form, Size and Physical Condition. The moon, like the earth, is very nearly round. Her diameter is 2,160 miles, and her volume is about 1-49 the size of the earttu and only ^^fa^^ times the size of the sun. The moon, to us, appears nearly as large as the sun. This is because she is about 400 times nearer to us. A ball thrown high in the air seems smaller than when tossed up but a few feet. Thus we see the appar- ent size of bodies depends largely upon their distance from us. 46 LUNAR TELLURIAN MANUAL. The moon, as seen through a telescope, presents a very uneven and broken surface, showing very high moun- tains, deep valleys, and the craters of immense volcanoes now extinct. The clouded or mottled appearance of its surface sometimes called " The man in the moon," and which many ignorant people think to be land and water, is really due to the difference in the reflecting power of the various portions of the moon's surface. The higher portions of her surface seem to be composed of lighter colored material than the lower, and they will therefore reflect more light than the darker colored and lower sur- face. If examined through a small telescope or field glass, we are able to see some spots on the lighter sec- tions brighter than the surrounding surface ; these are the summits of mountains, the most prominent being craters of volcanoes. The most careful observations of the moon fail to show any atmosphere. There can be no water, for the sun's heat during the long lunar days (about a month long) would evaporate it and produce a cloud-like film around the moon that could readily be seen. The results of observations upon the physical condi- tions of the moon are such that we must conclude that it is a cold, lifeless body, the essential elements of life, air and water, not being found. The Moon's Motions. The moon has three positive motions. 1. A revolution on her axis once in 29 ^ days. Thus we see the lunar day is 29^ times longer than the terres- trial. To an observer, on the moon near its equator, the sun would rise in the east and set in the west ; but the LUNAR TELLURIAN MANUAL. 47 period of time between sunrise and sunset would be equal to nearly 15 of our terrestrial days, and when the sun had set it would not rise for an equal period. How great must be the extremes of temperature ! The lunar day must be hotter than anything experienced upon the earth, while, during the lunar night the temperature must fall to a degree unknown save In the polar latitudes of our earth. To an observer on the moon, the earth would look like a huge moon 13 times larger than the moon appears to us. It would present the phases of the moon as we see them, but on a grander scale. Owing to the moon's slow axial rotation, the earth would not appear to revolve around it, but merely swing back and forth through a few degrees. 2. A revolution around the earth once in 27 1/3 days. 3. A revolution with the earth around the sun annu- ally. The result of the last two motions makes the actual path of the moon very peculiar. The second mo- tion mentioned, of itself, would carry the moon around the earth so that its path would be an ellipse ; while however, this movement is going on, the last mentioned movement (No. 3) is also in operation and is about 30 times as rapid as the former (No. 2), making the actual path an irregular curve, sometimes outside and some- times inside the earth's orbit; but its path always curves to the sun. The moon's orbital velocity is about 2,300 miles per hour, while she follows the earth in her great orbital journey at the rate of 68,000 miles an hour over a thousand miles a second* If the earth were at rest in her orbit the path of the moon would be similar to cut No. 1, (E the earth, M LUNAR TELLURIAN MANUAL. the moon, the arrows showing the direction of the moon's revolu- tion); Since the earth is not at rest, cut No. 1 shows the relative and not the true path of the moon. Let A in cut 2 represent part of the orbit of the earth, arid E B F will show the true path of the moon from her last to her first quarter, or while traveling from O to P, as shown in cut 1. The moon makes this path because she is carried forward with the earth around the sun from F to E while she is revolving around the earth from O to P, cut 1. If the moon's path from F to E were on the line G H, she would neither curve to nor from the sun, but be traveling on a straight line and at right angles to him. If this were true, at the point J, she would be over 400,000 miles from the earth then at I, but as the moon's dist- tance is about 240,000 miles, she must be at K instead of J. Hence, the moon's path must be on the line E B F, which is concave to, or curving towards the sun. After passing the point E the moon's orbit curves sharply in, and in 14 CUT No. i. LUNAR TELLURIAN MANUAL. 49 days crosses to the inside of the earth's orbit, as we ob- serve it does at the point F. The Sidereal and Synodic Revolutions of the Moon. The moon revolves around the earth in an elliptical orbit once in 27 1/3 days ; this is called the sidereal revo- lution. Sidereal means Star. Ask the pupils to observe that as the moon ball re- volves around the globe it is nearer the globe when on one side of it than when upon the other. In like manner the moon revolves around the earth ; sometimes she ap- proaches within 221,000 miles of the earth. Her great- est distance is 259,000. She seldom reaches these ex- treme limits ; her usual variations are about 13,500 miles either way from the average, which is about 240,000 miles. Ask the pupils to observe the position of the moon and some star near it in the heavens ; on the following evening the moon will have moved some distance to the eastward ; continue the observations through several evenings, and note the changes of the moon's position in the stars. In 27^ days (about) the moon will have passed clear around the heavens and will again appear near the star where it w r as first observed. The moon has now made one sidereal revolution (one revolution as re- gards the stars). If the sun and not a star were taken for the base of the observation, the time required for the moon to revolve around the earth and be brought to its former position relative to the sun would be 29^ days, about. This is a synodical . revolution. Call the pupil's attention to the fact that the sun ap- parently travels from west to east through the heavens, going clear around, or 3GO degrees in a year (about 365 50 LUNAR TELLURIAN MANUAL. days), and of course must travel on an average nearly a degree a day. The moon makes a complete revolution through the heavens in 27^ days, or about 13 degrees daily, and in the same direction that the sun apparently travels. Let us suppose the sun, the moon and a star to be in line on a given day ; on the day following, if ob- served, the sun will be seen about 1 degree east of the star, and the moon will be seen about 13 degrees east of the star and 12 degrees east of the sun. The following day the sun will be about 2 degrees east of the star and the moon will be about 26 degrees east of the star and 24 degrees from the sun. Observe that at this rate the moon will be 27 y$ days in passing around the earth and again getting into line with the star, thus completing the sidereal revolution. The sun in the mean time has passed to about 27 degrees east of the star, and for the moon to overtake him will require about 2 1-6 days additional, thus completing the sy nodical revolution in 29^ days. The change of the moon depends upon its relation to the sun and not to a star, so, from one new moon to another is 29^ days (about). The Phases of the Moon. The moon shines by reflected sunlight ; like the earth, one-half of her surface is illuminated by the sun, and when any part of the light hemisphere is turned toward the earth, we see that portion brightly illuminated, and the light it gives us we call moonlight. The moon acts as a great heavenly mirror reflecting the sun's light after he is gone. The bright side of the moon is of course always toward the sun. The Dark Moon. the pupils to notice that when the moon is be- LUNAR TELLURIAN MANUAL. 51 tween the earth and suri, the light hemisphere of the moon must be hid from the earth. Astronomically we say the moon and sun are in conjunction ; as ordinarily expressed, we say it is the " Dark of the Moon " or " No Moon." Pemonstrate this by the apparatus. New Moon- Move the globe forward in the orbit until the moon has passed two or three inches to the east of the pointer L. Ask the pupils to observe that the moon is not now between the globe and the arc S, but has passed to the eastward, and that now the hemisphere seen from the globe has a crescent of light around the western part and that the " Horns of the Moon " or the ends of the cres- cent point eastward. We say the moon is now new,* and being but little east of the sun, sets soon after him. At new moon when the air is clear we can plainly see the outline of the dark hemisphere. When the moon is situated nearly between the earth and sun as at new moon, the bright or illuminated hemisphere of the earth is towards the moon. Show this upon the apparatus mounted as in cut No. 1. An observer on the moon's dark hemisphere would now have, if we may be allowed the term, earthlight, in character similar, though in quantity greater than the light we receive from the moon when it is full. The sunlight reflected by the earth to the moon is in a diminished quantity re-reflected by her to the earth, and by this light twice reflected we see *Infact the moon the moment she passes between the earth and sun, or reaches conjunction, becomes " new," though she is not usually called new until the crescent is visible. Hereafter, in- this work New Moon means Conjunction. LUNAR TELLURIAN MANUAL. dimly the moon's dark hemisphere. The reason why the moon's crescent is brighter than the dark hemisphere, is because the light coming from it is reflected but once, while that from the dark hemisphere is reflected twice, the difference in brilliancy showing the loss by the second reflection. When new moon occurs while the moon is above the ecliptic, as shown in cut No. 1, the moon will be above as well as east of the sun, and her crescent must appear lower than when she is below the ecliptic. Thus we have what is called the " dry " and " wet " moon. First Quarter. Move the arm IX forward until the moon ball has passed one-fourth of the way around the globe from the arc S. To an observer on the globe the crescent of light during this movement will have increased until now one- half of the illuminated hemisphere is in view. The moon is now one-quarter of the way around the earth from the sun, and is in quadrature. The moon is now in her first quarter. Full Moon. Move the arm IX forward until the moon ball has passed one-half 'the way around the globe, and call the pupil's attention to the fact that an observer upon the earth would see the entire illuminated hemisphere of the moon, and that as she is almost directly opposite the sun she must rise at or near sunset. The moon is now in opposition with the sun and we have, illustrated, the phase of the moon called the Full Moon. LUNAR TELLURIAN MANUAL. 53 Last Quarter. Move the arm IX forward until the moon ball has passed three-fourths of the way around the globe and ask the pupils to observe, as this is done, that the illuminated hemisphere of the moon shifts to the eastward so that when it is brought to the three-quarter position only one- half of it is visible to an observer upon the globe. The moon is again in quadrature with the sun, and presents the phase of the moon in her last quarter, Old Moon. Move the arm IX until the moon ball is brought about half way between the last quarter and the dark of the moon, and observe that a crescent of light may be seen around the eastern side of the moon, the horns of the crescent pointing to the west. The moon is now " old," from which position she passes to conjunction and the dark moon, thus completing the common phases of the moon. The Orbit of the Moon. The orbit of the moon is an ellipse, her least distance from the earth is 221,000 miles, while her greatest dis- tance is 259,000 miles. She seldom, however, reaches these extreme limits, her usual variations from her mean distance of 240,000 miles, being about 13,500 miles each way. The orbit of the moon crosses the orbit of the earth at an angle a little greater than 5 degrees. This is shown (somewhat exaggerated) by plate E on the globe, which carries the moon ball in an inclined orbit above and below the ecliptic. The moon's declination is her distance north or south of the ecliptic. In cut No. 1 54 LUNAR TELLURIAN MANUAL. the moon is shown above the ecliptic in her greatest northern declination. In cut No. 2 she is shown below the ecliptic in her greatest southern declination. The Moon's Nodes. The nodes of the moon are the two points where her orbit cuts or crosses the ecliptic. The node where the moon crosses the ecliptic coming north is called her ascending node, and the opposite one the descending node. The pupils should fix clearly the moon's nodes in their minds, as upon this depends the understanding of much that is to follow. If the sun and moon could leave a thread of light to mark their pathway through the heavens (the sun's ap- parent annual path), we would observe these lines run- ning very near each other and to cross at opposite points of the heavens, so that as viewed from the earth the path of the sun would sometimes be above, and sometimes below the path of the moon, crossing it at opposite points the moon's nodes. These points of crossing are not fixed, but are constantly changing, falling back to the westward on the ecliptic or sun's apparent path about 20 degrees annually. If the nodes were stationary, then the time required by the sun to pass from one ascending node to another, manifestly, would be a year. Because of the moon's nodes revolving backward on the ecliptic about 20 degrees annually, he will approach her nodes about 19 days earlier than he otherwise would. Dis- carding fractions we have : 1 year, 365 days, less 19 days = 346 days the time required by the sun to pass from one ascending node to another. As the descending node LUNAR TELLURIAN MANUAL. 55 occurs midway between two ascending nodes, we have 346 days -r- 2 = 173 days as the time from the ascending to the descending node, and an equal period from the descending to the ascending nodes. Move the arm IX until the mooii ball is between the globe and the arc S, turn the plate E to the right until the center of the moon ball is opposite the pointer L ; the sun and moon are now at the node. Note the day of the month under the calendar index G. Move the arm IX forward carrying the globe around the arc S to its former position and, at the same time, turn the plate E about 1-18 the way around in the opposite direction, and ob- serve the sun has, because of this change in the position of the moon's orbit, passed the moon's node about 19 days earlier than he would have done had the moon's orbit not changed position- The Zodiacal Belt. The Zodiacal Belt is a band in the heavens lying 8 degrees on either side of the ecliptic, in which the sun, moon and the principal planets are seen to move. All the planets go around the sun in the same general direc- tion, from west, to east. The orbit of the earth, the ecliptic, is the base, and from it the inclinations of the orbits of the several planets are measured. None of the orbits of principal planets cross the orbit of the earth at an angle greater than 8 degrees and most of them cross at an angle considerably less. If all the planets could leave behind them a thread of light to mark their pathway through the heavens, we would see that within a belt of the heavens 16 degrees wide, lying 8 degrees on either side of the ecliptic, would lie the orbits of all 56 LUNAR TELLURIAN MANUAL. the principal planets, and in this belt they would be seen to move. This band or zone of the heavens is called The Zodiacal Belt." The Signs of the Zodiac. The ancient astronomers for some reason not now well known, divided the Zodiacal Belt into twelve equal parts of thirty degrees each, giving to each sign a name, be- ginning with the vernal equinox or the equinoctial col- ure, counting thirty degrees east and naming this "sign" 44 Aries;" to the next thirty degrees east they gave the name "Taurus," so continuing in the order shown upon the base of the globe. Thus we see that a "Sign of the Zodiac" is a portion of the heavens having a longitude or length of 30 degrees and a latitude or breadth of 16 degrees. Passage of the Moon Through the Signs of the Zodiac. We learned upon the previous page that the moon had her revolution in the Zodiacal Belt, and as she passes clear around the heavens, 360 degrees, in making her sidereal revolution, she must in that time have passed once through all the Signs of the Zodiac. If the moon passes through the 12 Signs of the Zodiac in 27 ^ days, (a sidereal revolution), she will occupy about 2*^ days in passing through one sign. Rotate the globe upon its axis until the ecliptic marked on the globe lies in a horizontal plane. If you were to take a large and wide barrel hoop and place it around the entire apparatus and hold it in such a position that the plane of the ecliptic extended to the hoop it would strike the middle of the hoop all the way around it; the LUNAR TELLURIAN MANUAL. 57 hoop would then show the position of the Zodiacal Belt for the Lunar Tellurian. Or, if the apparatus were placed'in a large tub, and water were poured in until one- half of the globe ball only remained above the water, the surface of the water would be the plane of the eclip- tic, and that portion of the tub, say 2 inches above and 2 inches below that surface would represent the Zodi- acal Belt. If the tub were made of twelve wide staves, each stave would represent a " Sign of the Zodiac." Let the globe move forward in her orbit, and the moon would be seen by an observer upon the globe, to pass through these signs upon the staves from west to east, as the moon in the heavens actually does pass through, or by the Signs of the Zodiac. When we say the moon is in Aries, we mean that the moon as seen from the earth is in that sign, or more prop- erly, between us and that part of the Zodiacal Belt called the sign Aries. A very instructive and interesting illus- tration may be given by placing the Lunar Tellurian upon a table and having the pupils, twelve in number, join hands around it. Let each one take the name of the sign nearest to him on the base of the globe. Move the arm IX forward, and when the moon ball, in passing around the globe, comes between the globe and one of the pupils, let that pupil speak the name of the sign he represents ; thus, Mary will say, when the moon ball is opposite her, "Aries;" in a moment it has passed Mary and is opposite John, who calls out, " Taurus," and so on through the twelve signs. Where the pupils join hands will mark the divisions of the signs. The writer strongly urges the use of the above illus- tration, for by it the children, though quite small, will get 58 LUNAR TELLURIAN MANUAL. a very clear conception of the Zodiacal Belt, the signs of the Zodiac and the way the moon passes through these signs. Passage of the Sun Through the Signs of the Zodiac The sun passes through the signs of the Zodiac in a. manner very similar to the moon, and the illustrations used to show the passage of the moon through the signs may be used to equal advantage to show the sun's pass- age. The sun passes through the twelve signs once every year and so occupies about one month in passing each sjgn. The pointer G, cut No. 1, shows at all sea- ST ns of the year the sign and the degree of the sign where the sun is situated. Thus, at the vernal equinox we see the sun is in the first degree of the sign Aries. Move the arm IX forward to June 21, and observe that in the mean time the sun has passed through the signs Aries, Taurus and Gemini, and has reached the sign Cancer. KoTE.When studying the change of seasons we saw that on June 2ist the sun reached its greatest northern limit 23^ degrees north of the equator, from which position it turned southward towards the equator. Thus we see the sun turns south at the moment he reaches the sign Cancer. We derive the word "Tropic" from the Greek word trepo, which means to turn. The word Cancer shows the position of the sun "when it turns southward, and from a union of these two we get "Tropic of Cancer." The same is true of the turning of the sun northward on December 22d, as it reaches the sign Capricornus, thereby giving us "Tropic of Capricorn.' 1 Passage of the Earth Through the Signs of the Zodiac. The earth is always said to be in the sign directly op- posite the one where the sun is situated. Thus, when the sun is in Cancer the earth is said to be in Capricornus, LUNAR TELLURIAN MANUAL. 59 where it would be seen by an observer upon the sun's surface. Eclipses. An eclipse in general, is the cutting off in whole or in part the sunlight, as it falls upon the earth or moon. All the planets are opaque ; they absorb in part the sun- light that falls upon them, and the remainder after ab- sorption is reflected back into space. No light passes through them. They cast shadows into space, the extent of these shadows depending upon the size of the planet and its distance from the sun. The larger the planet the larger the shadow, and the farther the planet is from the sun the farther the shadow will extend into space. To illustrate this, draw a circle on the blackboard a foot in diameter to represent the sun, mark this circle S ; two feet from this circle draw a small circle, say three inches in diameter, mark this circle E to represent the earth. Draw a straight line from the top of circle S to the top of circle E, continue the line a foot or more beyond E ; next, draw a line from the bottom of circle S to the bot- tom of circle E, and continue this straight line until it * O crosses the other line ; the distance from where these lines cross, to the circle E, represents the distance the shadow of the earth would extend. Draw another three inch circle, say four feet away from circle S, and draw similar straight lines from top to top and bottom to bot- tom- of the circles, extending them as in the other illus- tration, and ask the pupils to observe, that now the dis- tance from the crossing of the lines to the circle E is greater than in the first instance when the circles were closer together. Thus we see that the nearer a body of a given size is to the sun the shorter will be its shadow, 66 LUNAR TELLURIAN MANUAL. and the farther it is from the sun the longer will it ex- tend. Draw a straight line from the center of circle S through the center of circle E, and extend it until it reaches the crossing of the two lines before mentioned, and ask the pupils to observe that the line last drawn may represent the ecliptic, and that it divides the shadow, into two equal parts, one- half of which is above and one- half below it. So the earth into space casts her shadow, equal parts of which lie above and below the ecliptic. Thus we see : (a) That the shadows cast by any planet, great or small, must lie in the plane of that planet's orbit. (b) That the shadows cast by the planets are in the shape of a cone tapering to a point, the base of the cone being equal in diameter to the diameter of the planet, the distance to the point or frustum of the cone depend- ing upon the distance of the planet from the sun. (c) That the diameter of the shadow at any point de- pends upon the distance of that point from the body casting the shadow. The cone-shaped shadow of the planet is called its umbra, and to an observer situated in the umbra the sun is wholly obscured and to him the eclipse is total. Place the observer just outside of the umbra and the sun is not wholly obscured to him ; his situation is now in pen- umbra. To show the penumbra take the figures upon the blackboard used to show the umbra, and in addition draw a straight line from the bottom of circle S through the top of circle E and extend it a foot or two beyond. Draw another straight line from the top of circle S through the bottom of circle E and extend it as before, LUNAR TELLURIAN MANUAL. 61 the space beyond the circle E on either side of the umbra and between it and the lines last drawn shows the pen- umbra. The shadows of all heavenly bodies must have umbra and penumbra. Umbra means* totality, and penumbra, partiality. The Dimensions of the Earth and Moon's Umbra. The length of the earth's umbra is about 860,000 miles, or about 3^ times farther than the moon is from the earth. This is the average length : in December arid January (because then near the sun) the umbra is about 843,000 miles, while in June and July (when farthest away) her umbra is nearly 872,000 miles. The diameter of the earth's umbra at the distance of the moon is on an average about 6,000 miles, nearly three times the moon's diameter. The average length of the moon's umbra is 236,000 miles. It varies, however, from 221,150 to 252,640 miles. Observe that the average length of the moon's umbra is a little less than her average distance from the earth (240,000 miles). Therefore, if the moon having her av- ctge umbra pass between the earth and sun at her aver- age distance from us, the umbra would not reach the earth by nearly 4,000 miles. The eclipse in this case woidd be annular and not total. (See annular eclipses page 66). The greatest possible diameter of the moon's umbra as it falls upon the earth is about 175 miles, and this can be only when the moon is at her greatest distance from the sun and at her least possible distance from the earth. 62 LUNAR TELLURIAN MANUAL. Eclipses are known as solar and lunar, and as the terms indicate, they are of the sun and moon. Lunar Eclipses may be -j or Lunar Eclipses. If the moon revolved around the earth in the plane of the ecliptic she would pass through the earth's shadow and be eclipsed at every full moon, and would throw her own shadow upon the earth at every new moon. Her orbit is, however, inclined to the ecliptic, as shown by plate E on the globe. That she may pass through the earth's shadow and be eclipsed, the moon must, when full, be at or near her node, otherwise she will pass above or below the earth's shadow. It is not necessary that the moon be exactly at her node to strike the earth's shadow, for, if within 10 ^degrees either before or after the node, she will pass into the earth's shadow and be wholly or partially eclipsed, according to her nearness to or distance from the node when she " fulls." This distance, 10^ degrees either way from the node, is called the " lunar ecliptic limits." Thus we see, that at either node there is a lunar eclipse limit of 21 degrees ; includ ing both nodes, 42 degrees, within which limits all lunar eclipses must occur. Move the arm IX of the globe forward,, until the moon ball is brought to " full," as shown in cut No. 2 ; loosen the screw holding plate E, and turn the plate until the gear-wheel that drives the moon ball rests upon the lower part of the plate, as shown in cut ; tighten the LUNAR TELLURIAN MANUAL. 63 screw, ask the pupils to observe, that now the full moon is below the ecliptic (the line J, as marked upon the globe), and that the shadow of the earth will pass above the moon, and no eclipse will occur. IJ^ 33 // is important that the pupils remember, that while the relative sizes of the earth, sun and moon are shown, it is impossible to show their relative distances. If we were to do this, the globe should be placed about .a mile and a half from the arc S and the moon ball placed about 20 feet from the globe, and if placed at these distances, the moon ball must be at or very near the globe's ecliptic when full, in order to fall within the shadow ; a little variation above or below would cause .the moon ball to miss the globe's shadow altogether. If full moon occurs when the moon is a few degrees (say 10 degrees) before she reaches her ascending node, she will pass through the lower portion of the earth's- shadow, thus covering the upper part of the moon's sur- face with shadow, giving a partial eclipse of the moon. Should full moon occur when the moon is 10 degrees past her ascending node, her lower limb or edge would be eclipsed by the higher portion of the earth's shadow. Revolve the plate E one-half way around, and ask the pupils to observe that now the moon ball is above the ecliptic J, and that the shadow must fall below it. If full moon occurs when the moon is at or very near her node, the entire moon will pass through the earth's shadow and the eclipse will be total. Such an eclipse occurred .about midnight June 11, 1881. Solar Eclipses. There are but two celestial objects that can ever come 64 LUNAR TELLURIAN MANUAL. between us and the sun of sufficient size to cut off from us the solar light. These two are the moon and Venus. The passage of the planet Venus across the sun's face, is usually called a transit of Venus. The last transit of Venus occurred Dec. 9, 1874. The next will take place Dec. 6, 1882, after which no transit will occur until June 8, 2004. There are three classes of solar eclipses, viz. : total, partial, and annular. Let us treat them in their order. All eclipses of the sun, caused by the passage of the moon between us and the sun, must occur at new moon. Now, if new moon occur while she is in the vicinity of her node, an eclipse of some kind must occur. If she is at or very near her node, she will pass across the sun's face centrally, or very nearly so ; and if at this time she happens to be near enough to us, her umbra will reach some portion of the earth's surface, and to that region the eclipse will be total. On page 61 we learned that the greatest possible diameter of the moon's umbra at the earth is 175 miles; the usual region of totality is very much less. Thus we see why total eclipses of the sun are visible to so small portions of the earth's surface, while a lunar eclipse may be seen from any part of an entire hemisphere. The duration of solar eclipses is very much less than lunar. The length of totality in a solar eclipse cannot exceed 6 or 7 minutes, and is usually very much less, while the moon may remain totally eclipsed for nearly two hours. The apparent size of the sun and moon are very nearly the same, and it requires the entire body of the moon to hide the sun's disc and eclipse him wholly ; sometimes she is not able to do even this, as we shall shortly see. * LUNAR TELLURIAN MANUAL. 65 If an observer were stationed on the moon during a total lunar eclipse, he would, from his position, see a total solar eclipse. To him the apparent size of the earth and sun would vary greatly, the former appearing between thirteen and fourteen times larger than the lat- ter. The observer so stationed could not have an eclipse of the earth, as the largest shadow his little orb could cast upon us would not be half as large as the State of Illinois, and to him it would appear like a mere speck floating across the face of the earth. Outside of the field of totality in a solar eclipse the eclipse must be partial when it is seen at all. Suppose the city of St. Louis to be near the center of the field of totality of a solar eclipse. At the moment of totality in St. Louis an observer in St. Paul would see the moon as below the sun, and in the passage by, his face would ob- scure only the lower portion of it ; to him the eclipse is partial. An observer at New Orleans would see the moon passing rather above, hiding only his upper limb or edge, while a person in South America could not see the eclipse at all. Move the arm IX forward until the moon ball is brought to new moon, as in cut No. 1. Move the plate E until its highest point supports the moon ball, and ask the pupils to observe that, now the moon is above the ecliptic J, and the shadow of the moon must fall above and not upon the earth ; were they placed at their proper distance (20 feet). Move the plate E until the moon ball falls into the plane of the ecliptic, and ask the pupils to observe, that the shadow of the moon in this position must fall upon the earth. 66 LUNAR TELLURIAN MANUAL. On page 61 we find the average length of the moon's umbra is 236,000 miles, and her average distance from the earth 240,000 miles, so, should the moon pass across the sun's face when so situated the umbra would not reach the earth by some 4,000 miles. The apparent size of the moon is now smaller than the sun, and she would in this position be unable to hide his entire face from us, and when passing by his center, a ring or fringe of light would be seen all around the moon. An eclipse of this kind is called annular. The word annular means like a ring or ring shaped, referring to the ring or fringe of light seen around the moon. Thus we see that the moon must be nearer the earth than her average distance, or that the sun must be at a greater than his average distance to make it possible for the moon to hide his entire face and to produce a total eclipse of the sun. Move the arm IX forward, and ask the pupils to ob- serve, that the apparatus shows the moon sometimes nearer the earth than at others. * It is not necessary that new moon occur exactly at the moon's nodes to give an eclipse of the sun ; if within 16 y 2 degrees of it either way, she will eclipse him. Thus we see the " solar ecliptic limit " is 33 degrees at either node or, in all, 66 degrees for both nodes, and within this limit must all solar eclipses occur. Why more Solar than Lunar Eclipses. On page 62 we see the moon must be within 10 J^ de- grees (either before or after) of her node at Full Moon to enter the earth shadow, consequently her Lunar Eclip- tic limit is 10^ -f 10 5^ =21 degrees at either node, or a total of 42 degrees of her orbit wherein lunar eclipses LUNAR TELLURIAN MANUAL. 67 may occur. In the last section we see the solar ecliptic limit is 33 degrees at either node, or a total of 66 degrees in which solar eclipses may occur. Then it follows that the proportion of solar to lunar eclipses is the same as 66 bears to 42 or as 11 to 7. . Season of Eclipses. We have already learned (page 55) that the time from one node to another is 173 days. If a new moon occurs near ascending node and eclipse the sun, in 173 days fol lowing, full moon will occur near the descending node and she will pass into the earth's shadow and be eclipsed. Last year, 1881, the moon's nodes occurred about June 11, and December 1. This year, 1882, they occur about 19 days earlier, or about May 22, and November 11, and so continue from year to year, owing to the falling back of the moon's nodes. (See page 53.) The Solar Ecliptic limit 33 degrees, is equal in time to 36 days. So an eclipse of the sun may occur 18 days before or 18 days after the moon's node, which, the past year 1881, extended from May 23 to June 29 ; while the solar ecliptic limit for the opposite node embraces the time from November 12 to December 18. The Lunar Ecliptic limit 21 V degrees, is equal to 23 days, thus an eclipse of the moon may take place at any full moon occurring 11 y z days before or after the node. Thus the Lunar Ecliptic season is from may 30 to June 22, and from November 19 to December 12, of the year 1881. The Period of Eclipses. By referring to the subject of the moon's nodes (page 68 LUNAR TELLURIAN MANUAL. 54) we find the nodes are not fixed, but have a retrograde movement on the ecliptic, nearly 20 degrees every year, or at a rate that will carry them clear around the ecliptic in about 18 years, 5 months. If we mark carefully the position of the nodes on .the ecliptic now, and note the eclipses that occur for 18 years, 5 months, and record the result, and observe the phenomena for a like period fol- lowing, we shall find the eclipses for the latter period almost identical with those of the first. Knowing this the astronomers are able to foretell eclipses to the very day and hour a hundred years in advance of their occurrence ! These periods are called the Saros or Period of Eclipse. The Precession of the Equinoxes. The precession of the equinoxes is due to a gyratory movement of the earth's axis revolving the poles of the equator around the poles of the ecliptic. As the equa- tor or equinoctial and the ecliptic cut each other at an angle of 23^ degrees, so must their axis bisect. Upon the globe is marked the equator and ecliptic. The poles of the equator are the ends of the axis of the globe, and the poles of the ecliptic the points where a vertical line drawn through the center of the globe would cut its sur- face. This gyratory movement of the earth's axis is very slow, requiring about 25,800 years to complete one revo- lution. The effect of the movement is to carry* the equinoctial and solstitial points backward, slowly, around the ecliptic from east to west. The value of this move- ment annually is 50.1 seconds of arc. The earth's orbit, like all circles, is divided into 360 degrees, these degrees subdivided into minutes and the minutes into seconds. LUNAR TELLURIAN MANUAL. 69 The exact solar year* is the time required by the earth to travel 360 degrees of its orbit, less 50.1 seconds, or 359 deg., 59 min., 9.9 sec. To illustrate upon the globe the precession, or more properly the recession of the equinoxes, proceed as follows : 1. Arrange the globe as shown in cut II, page 9 ; ro- tate the globe upon its axis until the ecliptic upon the globe lies in a horizontal plane. 2. Move the arm O slowly to the left, completing a circle around the standard P, and observe that as this is done the poles of the equator describe circles around the poles of the ecliptic (the north pole of the ecliptic on the globe being where the 90th meridian east crosses the arc- tic circle). In like manner the poles of the earth de- scribe circles around the poles of the ecliptic once every 25,800 years, as before stated. 3. Adjust the globe for the calendar ; move the globe slowly forward to its orbit, and observe that the pointer ,X traces the ecliptic, crossing the equator, giving equi- noxes about March 20 and September 23. 4. Move the arm O a part of the way around the standard P, as in 2 above, say one-half of an inch; move it forward to its orbit, and observe that the equinoxes do not occur at the same points in the orbit as in the former instance, but earlier. Repeat the operation, moving the *Quite frequently called the Tropical Year. There are generally reckoned three years, i. Sidereal Year, as the time required by the earth to make one complete orbital movement, or 365 days, 6 hours, 9 minutes, 9 seconds. 2. The Solar or Tropical Year, as the time required for the sun's vertical ray to pass from tropic to tropic and return, or 365 days, 5 hours, 48 minutes, 46 seconds. 3. The Civil Year of 365 and 366 days, according: as the year is a common or leap year. 70 LUNAR TELLURIAN MANUAL. arm O little by little, and observe the equinoctial points falling back in the orbit as the arm O is moved. 5. The vernal equinox occurs as the sun enters the first degree of the sign Aries of the Zodiac. If these signs were fixed as regards the orbit, manifestly the next succeeding vernal equinox would occur 50 1 seconds before the sign Aries were reached, and so continue to fall back in the signs from year to year. The signs, how- ever, are shifted to agree with the falling back of the equinoxes ; thus the equinoxes will always occur in the same degree and sign as now. The signs, how- ever, do not agree with the constellations from which they derive their names. Equation of Time. Sidereal, Solar and Mean Time. Time is a measurement of duration. One of the first objects of astronomical study was to find a standard for the measurement of Duration. For this purpose the ap- parent diurnal revolution of the sun marked the begin- nings and endings of the standard days ; while this did not mark duration into uniform periods of time, it was found to be sufficiently accurate for the civil, and the crude astronomical uses of the earlier days. The sun-dial served to mark the subdivisions of the day ; but as the dial was useless in the night time or in cloudy weather, a more reliable indicator was sought in mechanical de- vices, similar to our clocks and watches. The makers of these were sorely perplexed because they could not make their machines " agree with the sun " for any con- siderable time ; because of this, we are told, the makers suffered persecution, and their machines fell into disre- LUNAR TELLURIAN MANUAL. 71 pute, and were little used ; and where used at all, they merely supplemented the sun-dial, by which they were " regulated " from time to time. It was soon discovered that the sun days were not of uniform length, and that the machines were the better time-keepers. The causes of this variation will be ex- plained before we leave the subject. The Sidereal Day is the period that elapses between two successive transits of any fixed star ; this period is unvarying. The length of the sidereal day is 24 sidereal hours, or 23 hours, 56 minutes, 4 seconds of "mean time." The Solar Day is the period tkat elapses between two successive transits of the sun ; this period varies in length, being sometimes more and sometimes less than 24 mean time hours. Thus it is that the clock and sun do not agree. The Mean Day or the Mean Solar Day is the aver- age length of all the solar days of the year, and is of course unvarying in length, and is the standard civil day which our clocks and watches are made to keep. The mean day is 3 minutes 56 seconds longer than the sid- ereal day. The varying lengths of the solar days depend upon two causes : 1. The unequal velocity at 'which the earth travels in its orbit. 2. The inclination of the equator to the ecliptic. 72 LUNAR TELLURIAN MANUAL. 1. To Illustrate that the Unequal Velocity of the Earth in its Orbit is a Cause of the Existing Variation of the Lengths of the Solar Days. Arrange the globe as shown in cut 2, page 36, and proceed as follows : Bring the calendar index to the 21st of June ; rotate the globe upon its axis until the prime meridian is under the pointer L ; extend the pointer L until it is within 1-16 of an inch of the globe. Move the globe forward in its orbit an entire revolution, and observe that the pointer L is by this movement carried from 'west to east across the meridians at a rate that will carry it clear around 360 degrees in one year of 365^ days (about), or a trifle less than a degree a day, on the average. This distance is equal in time to 3 minutes 56 seconds. Rotate the globe upon its axis from west to east, and observe that this movement carries the pointer L across the meridians from east to west at a rate that will carry it clear around in one day ; so it follows that while the daily rotation is carrying the sun's vertical ray 360 de- grees from east to west, the forward movement of the earth in its orbit is carrying it back nearly a degree (about 59 minutes of distance), from west to east. There- fore, the earth must turn more than once upon its axis to complete a solar day. This little " more " in a year amounts to 360 degrees, a revolution. So, the truth is apparent that the earth must turn 366 times upon its axis to complete 365 solar days ; or 366 sidereal days are equal to 365 solar days. If the movement of the earth in her orbit were uni- form day to day throughout the year, the variation would be uniform^ and the solar days would be of equal length. LUNAR TELLURIAN MANUAL. 73 As the orbital movement of the earth is not uniform,* and the daily revolution is uniform, a variation in the lengths of the solar days must follow. 2. To Illustrate that the Inclination of the Equator to the Ecliptic is a Cause of the Existing Varia- tion in the Lengths of the Solar Days. Arrange the globe as shown in cut 2, page 36. Bring the calendar index to the 20th of March, rotate the globe upon its axis until the ecliptic lies in a horizontal plane. Ask the pupils to observe : That the equator and the ecliptic are both great circles, and that a degree of one is equal to a degree of the other. That the earth rotates in the direction of the plane of the equator. The verti- cal sun travels on the ecliptic, a, Move the globe for- ward in its orbit a few degrees, and observe that this movement has carried the pointer L so many degrees east and north on the ecliptic, but has not changed its longitude to so great an amount as would have been the case if all the movement had been directly east, or with the rotation, instead of being at an angle to it. Briftg the calendar index to March 20, rotate the globe until the prime meridian is directly under the pointer L ; move the globe forward in the orbit until the pointer L, tracing the ecliptic, is brought to the 10th parallel. Observe that the orbit movement has carried the sun east and north ; rotate the globe slowly on its axis from west to *The velocity at which a planet travels depends upon its distance from the sun. The nearer to the sun the greater is his attraction, and the greater the velocity must be to keep the pianet from going- to him. The orbit of the earth is an ellipse, and the sun is situated in one of the foci. In obedience to this law the earth travels faster when near perihelion (Dec., Jan., Feb.,) than when near aphelion (June, July, Aug.) Other things being equal, it follows that the solar days are longer in Winter than in Summer. 74 LUNAR TELLURIAN MANUAL. east, and observe this movement carries the pointer L back to the prime meridian not on the line of the ecliptic, but following the parallel. Thus the orbital movement carries the sun forward on an angle, and the daily rota- tion brings it back on a straight line describing two lines of a triangle, of which the ecliptic is the hypothenuse, a parallel of latitude and the prime meridian being the other two sides. Owing to the angling movement about 1-12 of the displacement is lost, thereby shortening the solar day 1-12 of 3 minutes 56 seconds (the average displacement), or about 20 seconds, b. Move the globe forward to the position it occupies about the 1st of June, and observe that from this time until about August 1st the movement of the sun on the ecliptic is nearer in the direction of the rotation than in March. Also, that a degree on the ecliptic is greater than a degree upon the parallels to which the sun is, at this season, vertical, and the daily rotation is slower.* Owing to this, about 1-12 of this displacement is gained, thereby lengthening the solar day 1-12 of 3 minutes 56 seconds, or about 20 seconds. The Tides. The Subjoined Explanation of the Mathematics of the Tidal Movements is by Prof. E. Colbert, the well known Astronomer of the Chicago Tribune. The waters of the ocean are in ceaseless motion, rising and falling twice in each lunar day, or about every 25 *The surface of the earth at the equator travels faster in its diurnal motion than the surface at the the tropics, being nearly 250 miles farther from the tarth's axis LUNAR TELLURIAN MANUAL. 75 hours. The rising of the waters is called the flow or Hood tide, and the falling of the same the ebb tide. The height to which the waters rise through a number of succeeding tides is not uniform, as will be explained here- after. The greater are called Spring, and the lesser Neap tides. The waters act in obedience to that one universal law of gravity, which may be expressed as follows ; All bodies attract all other bodies throughout space directly in proportion to the quantity of matter they con- tain, and inversely as the squares of the distance be- tween them. We may further add that the force of at- traction is exerted in the direction of a straight line join- ing their centers of gravity. The subjoined example will explain the application of this law. Let two bodies be placed ten feet apart, the weight of A to be 2 tons and that of B 1 ton ; their attraction for each other is directly as their matter, or as 2 is to 1. Let 10 equal the power of attraction of A for B and 5 equal the power of attraction of B for A. Separate the bodies 20 feet ; they now attract each other in the same ratio, i. e. 2 to l,but with diminished power. The square of the first distance (10 feet) is 10 X 10 = 100. The square of the second distance (20 feet) is 20 X 20 = 400. According to the law above given the attract- ing power of A and B in the two positions is inversely, as 100 is to 400, or directly, as 400 is to 100, or as 4 to 1 in the respective distances of 10 and 20 feet. Thus we see that at 10 feet the attractive power is four times greater than it is at 20 feet. If, as stated, the attracting power of A for B at 10 feet is 2, at 20 feet it is 2 -f- 4 76 LUNAR TELLURIAN MANUAL. = f or . For B at 10 feet the power is 1, at 20 feet it is 1-4 =^. The average tide producing influence of the moon as compared with that of the sun is nearly as 2^ is to 1. The tides in open ocean do not rise to exceed 5^ feet, while in the breakers of the tidal wave as it reaches a continent the water rises very much higher. In the Bay of Fundy, the waters sometimes rise nearly 100 feet. At Boston the tide is usually^bout 14 feet. The tides of our oceans are due to the difference be- tween the attractive force exerted by the moon and sun ; on the earth as a whole, and on the waters at her sur- face. The following explanation of the theory of the tides only applies strictly to such parts of the ocean sur- face as are not near to considerable masses of land sur- face. The retardation of the tidal wave in moving through shallow water, with the changes in its direction, speed, and volume, caused by continents and islands, are matters which belong more to physical geography than to astronomy. It may be well to note, however, that even in the deep waters of the mid Pacific, the tidal wave is retarded by the same cause that makes it travel behind the moon instead of keeping directly under her ; fric- tion. The tide wave that^gathers on the eastern side of the Pacific Ocean follows about two hours behind the moon, and occupies about 40 hours in passing round to our Atlantic coast ; less than a cercumference of the globe. Let M represent the position of the moon ; A D the earth, and E its center. If we take E A, or E D, the LUNAR TELLURIAN MANUAL. 77 earth's radius, as unity, then, for the least possible dis- tance of the moon ; MA = 55 ; ME = 56 ; and MD Let m denote the measure of the moon's attractive force at the unit of distance ; it equals about 375,800 feet. Then the disturbing force on the water at A will be measured by m m (55)~ 2 (56)* 5= 4 -40 feet - Similarly ; the moon's disturbing force on the water at D is measured by : m m (56f (5T) 5 ; = 4-17 feet. 2 m We may also calculate that pgjja = 4-28 ; which is the mean of the above results, and is the mean tide due to the moon acting at her least possible distance. The calculation gives 0*12 more for the tide under the moon, and 0-11 less for the opposite tide. The differences are really much less than this ; owing to the fact that the crests of the two tides are at a and d instead of on the line AD. In the open ocean they lag about 43 degrees behind the place of the moon, and its opposite ; and are still more retarded when they meet with land masses. 78 LUNAR TELLURIAN MANUAL. The greatest possible distance of the moon from the earth's center is about 64 times the earth's equatorial radius. Calculating as before, we have : m m Direct tide = 2'94 feet. m m Opposite tide = (64)2 ^5^2 ; = 2'80 feet. 2 m Mean tide (54)3 ; = 2-87 feet. In this case, as in the other, the tide equals %m divided by the cube of the relative distance from the earth's center, plus and minus a small quantity. All perturbations due to the force of attraction vary inversely as the cube of the relative distance, plus or minus a correction which decreases with an increase in the rela- tive distance. The least and greatest distances of the moon in her {average) orbit, are about 57 and 63^. These corre- spond to 4*06 feet, and 2-94 feet respectively. Half the sum of these two is 3*5 feet, which is about the average height of crest of the lunar tide wave in the open ocean. The sun also causes a tide. Our distance from him when in Perihelion is 23,020, and when in "Aphelion 23,805 times the earth's equatorial radius. The value of m^ for these assumptions of distance of the sun, is 8,900,000,000,000, nearly. The resulting values of the solar tide are 1-44 and 1-30 feet ; average 1'37 feet. The lunar and the solar tides move after the place of their respective causes in the heavens, as the earth turns round under them. At the times of New and Full Moon the two forces coincide, and the united tide is equal LUNAR TELLURIAN MANUAL. 79 in magnitude to the sum of the two : being (4*06 -f- 1'44) =5'50 feet, when the earth is nearest to sun and moon ; and (2-94 -f 1-30) = 4-24 feet, when both are at their greatest distance. When the moon is in her first or third quarters, the depression caused by the sun coincides with the elevation caused by the moon ; and the tide varies from (4-06 1-30) = 2-76 feet, when the moon is in perigee and the earth in 'aphelion, to (2-94 1-44) =1'5 feet, when the moon is in apogee and the earth in peri- helion. The crest of each direct tide is theoretically 40 to 45 degrees or about 2 hours 50 minutes, late on the parallel of latitude corresponding to the declination of body caus- ing the tide. That is, if the moon be in 20 degrees north declination, the direct lunar tide will be in 20 degrees of north latitude. The crest of the opposite tide is, simi- larly, moving in latitude opposite to the declination. Let u denote the angular distance of any point on the earth's surface from the crest of the lunar wave at a given mo- ment ; iv its angular distance from the crest of the solar wave at the same instant ; ^4, the height of the lunar crest ; and B, the height of the solar crest. Then the height of the tide at the designated time and place, will equal : A. cos. (2 u] + B. cos. (2 -w) : remembering that the cosine of an angle greater than 90 degrees and less than 270 degrees, is essentially negative. READ THE OPINION OF CAPABLE JUDGES : " HEADQUARTERS ILLINOIS TEACHERS' ASSOCIATION, SPRINGFIELD, DEC. 29, 1880. " A. H. ANDREWS & Co., " Gentlemen : Your new Lunar Tellurian Globe is a splendid apparatus for class use in illustrating Mathematical Geography. The relationships of the earth, sun and moon are well and clearly shown. The Globe has more merit and fewer defects than any similar apparatus we have ever seen. It is a credit to the inventor and manufacturers. Yours respectfully, "M. L. Seymour, of Normal University, Bloomington. " E. A. Gastman, Supt. Schools, and President Illinois Teachers' Association. " D. S. Wcntworth, Principal Cook Co. Normal School, Engle- wood, 111. " Henry L. Boltwood, Principal Ottawa Township High School- Ottawa, 111. " M. Andrews, Supt. City Schools, Galesburg, 111. " Leslie Lewis, Supt. Schools, Hyde Park, 111. "J. Pike, " " Jerseyville, 111. " W. H. Williamson, Prin. Schools, Havana, 111. " R. W. Mathews, " " Chester, 111. " Geo. Blount, Supt. Schools, Macomb, 111. Letter from Prof. E. COLBERT, Astronomer of the Chicago Tribune. CHICAGO, ILL., May, 2. 1881. A. H. ANDREWS & Co. Gentlemen: I have carefully examined your " Lunar Tellurian " and am charmed with it. The apparatus may be used to illustrate many of the phenomena that are due to the move- ments of the earth and moon, with reference to the sun; and con- veys a much clearer idea of the same than has hitherto been obtained by the great majority of those who have essayed to understand them. So far as I know, it is unequaled. Very respectfully, E. COLBERT. The Solar System.* THE SOLAR SYSTEM, as known to us through the discoveries of Copernicus , Kepler, Newton and their successors, consists of the Sun as a central body, around which revolve the major and minor planets with their satellites, a few periodic comets, and an unknown number of meteor swarms. The bodies of the system may be classified, as follows : i. The SUN, the center of our portion of the universe or the solar system. 2. The four inner planets. Mercury, Venus, Earth, Mars. 3. A group of small planets called Asteroids revolving outside of the orbit of Mars. 4. A group of four outer placets, ^Jupiter, Saturn, Uranut and Neptune. 5. The satellites revolving about their primaries the planets. 6. A number of comets and meteor swarms revolving in very eccentric orbits about the sun . The 8 planets of groups 2 and 4 are called Major planets to distinguish them from the 200 or more Minor planets of group 3. The relative sizes of the planets if viewed from an equal distance from all of them would be somewhat as follows : Jupiter, \% inches in diameter ; Sat- urn, i% inches ; Neptune, 9- 16 inches ; Uranus, % inch ; Earth and Venus less than % inch ; Mars a pin-head, and Mercury a little more than a point. The relative sizes of the Sun as seen from the different planets would be somewhat as follows: Frorri Mercury the sun would appear i^ inches in diameter ; from Venus, % inch ; from Earth, y z inch ; Mars, % inch ; Jupiter, i-i6inch; Saturn, 1-20 inch; Uranus, 1-50 inch; Neptune, a mere point. If we represent the sun by a gilded globe, 2 feet in diameter, we must show Vulcan and Mercury by mustard seeds ; Venus by a pea, Earth by another, Mars by half that size, Asteroids by the motes in a sunbeam, Jupiter by a small orange, Uranus by a cherry, and Neptune by one a little larger. The relative distances of the planets from the sun may be represented approximately by the^e figures : Mercury 4, Venus 7, Earth 10, Mars 15, Ceres (a Minor planet) 28, Jupiter 52, Saturn 95, Uranus 192, Neptune 300. THE SUN. The distance of the Sun from us is said to be about 92% million miles. No one could even count this number in a year's time ! The diameter of the Sun is 860,000 miles ; hence his radius is twice the mean distance of the Moon from the Earth. The Sun's volume is 1,300,000 times that of the Earth, and his mass over 700 times that of all other bodies, including Earth. Hence, the center of gravity of the whole system is very little outside of the body of the Sun, and will be inside of it when Jupiter and Saturn are in the opposite direc- tions. The Earth receives less than one two billionth part of the solar heat or radiation ! How much heat then is lost in space ! Hut suppose the source of our heat supply to b j gradually diminished for some cause, how fatal the con- sequence to the inhabitants of Earth ! Among the theories as to the source of heat supply in the Sun is this, viz : that there is a constant contraction of the solar sphere. Theory indicates that in five millon years the' Sun will be reduced to half its present size. His density is about one-fourth that of the Earth. Zollner says the sun revolves on its axis at the rate of 660 miles an hour. MERCURY. But little is known of this planet. Being so near the sun it can be seen only just after sunset or before sunrise, and scarcely ever visible without a telescope Mercury and Venus have much in common, both being within the orbit of the Earth. Mercury is about 36 million miles from the Sun. His diameter is about 3,000 miles. His year 'is about 88 of our days. Axial revolu- tion about same as ours; orbital velocity, 1773 miles a minu'e. VENUS. This is called the second planet, her year being about 225 of our days ; distance from sun, 66,750,000 miles ; diameter, 7,660 miles ; orbital veloc- ity, 1,300 miles a minute. Venu's may be as near Earth as 22,000,000 miles, or as far as 160,000,000. EARTH. This is the third planet in distance from the Sun, and moves in her yearlv orbit 69,000 miles per hour, 1,152 miles per minute, or 19 miles per second. In our daily revolution, we, of course, move at the rate of about 1000 miles per hour. *These items are compiled from Newcomb and other sources, by E. N. A. MOON. The Earth being larger than her satellite, we can see more than half her surface, sav 58-100. The difference in heat on the Moon at noon and midnight, is 500 degrees. The Moon gives us only 1-618,000 as much light as the Sun. The sky full of moons woufd not give us daylight. There have re- cently been discovered some signs of atmosphere on the moon, it is thought. MARS. The fourth planet of the system has a year of about 687 days ; dis- tance from sun, 141 million miles ; diameter, 4,211 miles. It has two moons; day about the same as ours ; orbital speed, 900 miles per minute. JUPITER. The fifth planet, has -) moons ; distance, 480 million miles ; vol- ume 1-1,000 that of sun. His days, gh. 55m. 203. He has four satellites ; diam- eter, 86,000 miles. His year equals 12 of ours ; velocity, 483 miles a minute. SATURN. Annual revolution around the sun 29*4 years ; distance from sun, SSi million miles ; diameter, 70,500 miles : volume 700 times that of Earth. Den- sity, less than that of any other heavenly body, or less than water. Day, loh. I4m. 243. It is the most remarkable planet on account of its belt and 8 satellites. URANUS. Revolves about the Sun in 84 years ; diameter 50,000 kilometres ; has two known satellites ; is distant from sun 1,770,000,000 miles. His year is 84 of ours. NEPTUNE. Little is known of this planet. His mean distance is nearly 3 billion miles; periodic time, 164 years; has i moon; diameter, 55,000 kilo- metres, or 34,520 miles. The air roofs us over and retaining the heat of the sun keeps us warm. The sun's constant force displayed on the earth, is equal to 543 trillions of engines of 400 horse power each, working day and night ! A man weighing 150 Ibs. on earth, weighs 396 on Jupiter. Earth is 3,236,000 miles nearer to sun in winter than in summer. Hence it is hotter in the summer of the southern hemisphere than in the northern summer. SPACE has probably no resisting medium ; its temperature is about 200 de- grees below zero. I..IGHT goes 185,000 miles a second. The nearest fixed star is 16 billion miles distant, and it takes three years lor its light to reach us ! The highest speed of a rifle ball is 2,000 feet per second . The diameters of the asteroids are from 20 to 400 miles. Mass of all of them put together less than one-quarter of earth. Arago thinks there are about 18 million comets traversing our system. They are thought to be fluid or vapor. STARS. There are about 5,000 visible in the whole heavens, both north and south. There are 20 of the ist magnitude, 65 of the 2nd, 200 of the 3rd, 400 of the 4th, 1,100 of the 5th, 3,200 of the 6th. But of the 7th magnitude there are 13000 stars, the 8th 40,000, the 9th 142,000. In the Milky Way, there are 18 million stars, and when we consider that we are on one of the stars of the Milky Way, how wonderful the works of creation, and how insignificant, rela- tively is the earth ! School Apparatus Of all kinds, and very best quality, such as Globes (60 kinds), Blackboards, Liquid Sla'ing 1 for same, Outline Maps, Anatomical and Reading- Charts, Nu- meral Frames, Andrews' Slate Drawing Book, Noiseless Slates, etc. Map and Blackboard Pointers, with and without Lineal Measures. No Crayon we have ever been compares with the new Alpha Dustless. It makes a clenn white mark, is not greasy and does not scratch the board. It outlasts six chalk crayons . The demand for it is unprecedented. Samples sent teachers on application. 75c per gro-s. 5 gross for $3 50 Dustless Blackboard Eraser. (Patented,) And the Best Ever Used. Only 91.80 Per Dozen. Sample sent on receipt of 150. It is enough to say that^teachers consider this the best Eraser for the price they have ever tried, :tnd the most free from dust. The cut on the right shows the Globe Case which is sent with all S and 12 inch globes It may be hung up on the wall i the school room as shown in cut, or closed and locked at night. Our new, complete and handsomely Illus- trated Catalogue of School Merchandise will be mailed any one on receipt of 20 cts. Address for all particulars the Manufacturers, A. H. Andrews & Co., 195 and 197 Wabash Ave., Chicago. The Triumph School Desks. Dovetailed and Doweled Together. Both Stationary and Folding Top. These Desks, of such acknowledged superiority in construction to any nml all other desks, received the highest awards at both the Philadelphia and Paris Expositions ! This meant something at the time, and it means something still ! Educators and School Officers who wish to know the requisites of a first- class desk, and WHY the TRIUMPH has and must continue to take the lead, will please send for our Descriptive Circulars of Desks and all kinds of School Merchandise. The New Folding Lid Desks. The lid and seat are folding and reduce the space to the minimum. The lid assumes four positions. Two for study, one for writing and one as when closed and locked upon the book box. Address the Manufacturers, A. H. Andrews & Co., 195 and 197 Wabash Ave., Chicago, 111. THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. SEP 28 933 SEP 29 Wo REC'D LD | OCT 3 1957 LD21-100m-7,'33 1 11 8ft I