The true figure of the earth is therefore as nearly as possible that of a spheroid, corresponding to the form that would be produced by the revolution of an ellipse about its minor axis-the major axis or equatorial diameter being 41,852,124 feet, and the minor axis or polar diameter 41,710,242 feet.

The highest elevations and the greatest depressions of the surface do not affect the general sphericity of the earth as a whole; the height of Mount Everest, the most elevated of the Himalayan peaks (equal to about th part of the earth's diameter), would be represented on the largest artificial globe by a minute grain of sand.

The cause of the compression or flattening at the poles is the earth's rotation. The effect of rotation upon a spherical body is to cause the parts which are in most rapid motion to bulge out, and those near the axial line to sink correspondingly. This is clearly shown if we place two flexible hoops at right angles, and pass a straight rod through them where they intersect each other. When at rest they are round, when rapidly rotated they assume the spheroidal form.

The Circles of the earth are lines supposed to be drawn com

pletely round it. They are distinguished as Great Circles and

Small Circles.

All Great Circles, as we have already seen, divide a sphere into two equal parts or hemispheres, while all Small Circles divide it into two unequal parts. All Great Circles of the same sphere are equal; Small Circles of the same sphere diminish as they approach the extremities of the axis of the sphere.

The Equator is a Great Circle drawn round the earth midway between the poles, that is, at exactly the same distance from each pole.

The equator divides the globe into two halves or Hemispheres-a Northern Hemisphere and a Southern Hemisphere. The Northern Hemisphere is that half of the globe which is between the Equator and the North Pole, and the Southern Hemisphere is the half that is between the Equator and the South Pole.

A Parallel is a small circle drawn in a direction parallel to the equator.

Any number of parallels may, of course, be drawn between the equator and the poles. The earth's revolution, however, fixes the position of four chief or Constant Parallels, namely, the Tropics and the Polar Circles.

The Tropics mark the furthest distances on either side of the equator within which the sun is vertical.

These points are respectively 23/21⁄2° N. and 231⁄2° S. of the Equator. The circle drawn round the globe at 23% to the north of the equator is called the Tropic of Cancer; the similar circle drawn at 231⁄2 south of the equator is called the Tropic of Capricorn.

The Polar Circles are small circles drawn round the globe in a direction parallel to the equator, and at a distance of 232° from either pole.

The circle drawn at 2321⁄2° from the North Pole is called the Arctic Circle-that drawn at 23% from the South Pole is called the Antarctic Circle. These circles mark the limits (from either pole) within which the sun remains wholly above the horizon for a term of more than 24 hours at one season of the year, or does not rise for a term of more than 24 hours at the opposite period of the year.

Zones.-The Tropics and Polar Circles serve to divide the surface of the earth into Five Zones-one Torrid Zone, two Temperate Zones, and two Frigid Zones.

The Torrid Zone extends on either side of the Equator from the Tropic of Cancer on the north to the Tropic of Capricorn on the south. It is thus nearly

47° or 3,238 miles in breadth, and includes the hottest part of the globe, because the sun is vertical or directly overhead to every place within it twice a year.

The Frigid Zones embrace the area within the Polar Circles, and are the coldest parts of the earth, because there the sun is, during a portion of the year, wholly absent, not rising above the horizon for weeks (or months) in continuous

succession.

The Temperate Zones lie between the Torrid and the Frigid Zones, and are, as their name implies, neither so hot as the Torrid nor so cold as the Frigid Zones. The North and South Temperate Zones are each 43° broad.

Area of each Zone.-Of a total area of 197,000,000 square miles, the Torvid Zone embraces 78,406,000; the Temperate Zones, each 51,121,500; and the Frigid Zones, each 8,175,500.

Parallels: But besides the Equator and the Four Constant Parallels that mark the limits of the various Zones, we can draw a circle or parallel through any place north or south of the equator, so that there is practically no limit to the number of parallels. All places exactly east or west of each other are said to be on the same parallel.

Latitude: The position of places relative to the equator and the poles are indicated by their latitude, that is, their distance, measured in degrees, from the equator towards either pole.

Latitude is thus the distance in the direction of north and south, and as all complete circles, great and small, are divided into 360 degrees, the greatest latitude which a place can have is 90 degrees, that is, the extreme distance of either pole from the line of the equator. The latitude of all other places must be less than 90 degrees. All places situated between the Equator and the North Pole are said to be in North Latitude, and all places between the Equator and the South Pole are said to be in South Latitude.

Low Latitudes and High Latitudes are general terms used to indicate nearness to the equator and the poles respectively.

Length of a degree of Latitude: Were the earth a perfect sphere, the length of a degree of latitude would be exactly the same at all places, but as the earth is slightly compressed at the poles, the length of a degree of latitude varies slightly, increasing from 68.7 miles at the equator to 69.4 miles at the poles.

In

Parallels of Latitude are usually drawn on globes and maps at every 5°, 10°, or 20° apart. If the map is on a large scale, each degree, or part of a degree, is indicated. maps, the equator and parallels of latitude are represented by straight or curved lines extending from right to left.

But latitude alone does not enable us to fix the exact positions of places on the earth's surface.

Thus, if we are told that a place is in 50° N. Lat. we only know that it is somewhere on the circle or parallel 50 degrees north of the equator, but at what point on that parallel the place is to be found is not indicated, and yet it must be done before we can point it out or mark its position. For instance, in order to fix the position of a certain point within a square we must determine its distance, not only from the top or bottom of the square, but also from one of the sides. In the same way, in order to fix the exact positions of Places on the earth's surface we must know their distance, not only north or south of a given point or line, but also east or west of some fixed point or line.

The rotation of the earth enables us to fix two invariable points-the Poles-and by assuming a line to be drawn round the earth midway between them, we get an initial line or circle-the Equator-from which we can measure distances in the direction of north or south, i.e., we can fix the latitude of a place. But we have no such fixed points to determine distances east or west, and besides, north and south are absolutely fixed directions, and never change, while east and west indicate relative direction only, and constantly change with regard to places on the earth's surface. Thus a place to the east of us is, when we go beyond it, to the west, and so on. We can, however, fix initial points or lines from which to determine distances east and west, with the same certainty as parallels of latitude indicate distances north and south of the equator.

Meridians: As the earth rotates on its axis, all places directly north or south of one another have mid-day or noon at exactly the same time.

Now a line joining all places that have mid-day or noon at the same time would pass in the exact direction of north and south. All places on this line are said to be on the same meridian (Latin, meridies, mid-day). A Meridian is thus a line drawn round the earth in the exact direction of north and south, that is, passing through the poles, and crossing the equator at right angles.

Such a line may be supposed to pass through any given place on the earth's surface (and may, of course, be actually drawn upon the surface of the artificial globe); it is then called the Meridian of that place. Thus a line drawn through London in the exact direction of north and south is called the Meridian of London.

As Meridian Lines may be supposed to be drawn through any and every place, there is, therefore, virtually no limits to the number of meridians that may be drawn. They are not, however, drawn at intervals of less than one degree, except on maps on a large scale, and in ordinary atlases the intervals may be 5, 10, or even 20 degrees.

In order to enable us to express distances east or west, we have to fix upon some one of the meridians as an initial or First Meridian. In our own country we take the meridian, supposed to pass through our National Observatory at Greenwich, as the initial or Prime Meridian, and from it we measure all distances to the east or west.

Longitude: As parallels show the latitude, so meridian lines serve to show the longitude of places.

Meridians are generally drawn on globes and maps of the continents of the world at intervals of 5, 10, or 20 degrees apart, and the longitude of a place is stated as so many degrees east or west of Greenwich. (Abbreviated thus: London, o° 5' W.; Melbourne, 1.44° 59′ E.)

of

A Meridian Circle is a great circle passing through the poles and dividing the earth into two equal parts-an Eastern and a Western Hemisphere. In maps the "World in Hemispheres," the meridian of 20° W. is generally assumed as the dividing circle. A meridian is half a meridian or great circle, and only extends half-way round the world, that is, from pole to pole. (Every parallel is a complete circle).

Longitude, then, is distance to the east or west of a given meridian, and is measured halfway round the globe, that is, 180 degrees upon each side of any meridian; and it is called East Longitude or West Longitude according as it is to the cast or to the west of the meridian that is used. 1

The greatest longitude which a place may have is therefore 180° E. or 180° W. (both indicating the same line), while the highest latitude is 90° N. or go' S. (two different points 180° apart).

Length of a degree of longitude: As all meridian circles are great circles, and all great circles are equal, while the parallels are small circles gradually diminishing in size from the great circle of the equator to o at the poles, the length of a degree of latitude is practically invariable, while the length of a degree of longitude varies constantly, decreasing from 69 miles at the equator to o at the poles.

At the Equator, therefore, the degrees of latitude and longitude are very nearly equal in length, i.e., 60 geographical or 69 statute miles. At lat. 10° N. or S. a degree of longitude is 67.96 statute miles; at 20°, 64.79 miles; at 30°, 59.75 miles; at 40°, 52.85 miles; at 50°, 44.35 miles; at 60°, 34.5 miles; at 70°, 23.6 miles; at 80°, 11.98 miles; at go, or the poles, a

The length of a degree of longitude at the equator may be found by dividing the circumference of the earth by 360, and similarly at any other point north or south of the equator. Thus, at the equator, it will be (24,900 ÷ 360) miles 69 miles at, say, 50° N. or S. (the parallel measures about 16,000 miles), it will be (16,000 ÷ 360) miles = 441⁄2 miles. Conversely, if we wish to find the circuit of the earth along any parallel, we multiply the length of a degree of longitude on that parallel by 360. Thus the circuit at 40" N. or S. will be (52.85 x 360) miles: at 80′ N. or S. (11.98 × 360) miles.

Longitude and Time: Latitude is expressed in degrees only; longitude may be indicated in time as well as in degrees.

As it is noon, or mid-day, at all places directly north or south of one another, i.e., on the same meridian, and as the earth's rotation brings each of the 360 meridians exactly opposite the sun, once every 24 hours, it follows that the sun seems to pass over (360°÷ 24), or 15° in one hour. Hence a place 15° east of a given point will have its noon one hour sooner, while a place 15° west of the same point will have its noon one hour later.

Longitude may thus be expressed in time as well as in degrees, and the one is convertible into the other at the rate of 15° to 1 hour. Thus, the longitude of Khiva is equally well expressed as 4 hours before Greenwich, or 60° E., and that of New Orleans as 6 hours after Greenwich, or go" W.

Local Time: A difference in longitude of only 1 or 69 miles, makes, therefore, a difference in time of 4 minutes, so that the local time at different places, even in a small country, will vary considerably. In England, for instance, the local time at Liverpool, 3' west of London, is 12 minutes behind the local time of the metropolis; while at Yarmouth, 1°40' east of Greenwich, it is 6 minutes earlier than the local time at Greenwich. Mean Time: These constant differences in local time, and the requirements, especially of railway and postal services, render a

Standard of Time absolutely necessary; and in all civilised countries such a standard is found in the Mean Time of the capital or the chief observatory of each country. And as in England we measure the longitude from the meridian of Greenwich, so the time kept all over the country is Greenwich Mean Time. In France, the meridian of Paris is taken as the Prime Meridian, hence Paris Mean Time is used. In Germany, Belgium &, the time standard is that of 15′ East of Greenwich.

In the United States and Canada, the differences in time over such a wide extent of country are so great as to preclude the adoption of any single standard of time, as in European countries.

Different districts had thus different standards, but the use of so many different standards caused so much confusion that in 1883 a new

Railway Time Standard was adopted. By this system the country is supposed to be divided into belts or sections of 15 each. The mean time of the central, or governing meridian in each belt, is taken as the standard for 71 on either side; and as the time difference between successive central meridians (15° apart) is exactly one hour, the hour

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hands in the different sections indicate different hours, but the minute and second hands point exactly the same. The differences thus consist of even hours; the minutes and seconds are the same for all sections.

The Governing Meridians are the 60th, or standard for Intercolonial Time (i.e., Nova Scotia, New Brunswick, &c.), the 75th for Eastern Time (N. E. States), the goth for Central Time, the 105th for Mountain Time, and the 120th for Pacific Time. Eastern Time is thus exactly one hour behind Intercolonial Time, and one hour before Central Time. Pacific Time is one hour behind Mountain Time, two hours behind Central Time, and three hours behind Eastern Time. Thus when it is 12-10 p.m. at New York (E.T.) it is 11-10 a.m. at St. Louis (C.T.), 10-10 a.m. at Denver (M.T ), and 9-10 a.m. at San Francisco (P.T.)

The same principle could be easily applied to a synchronous system for European Countries and the rest of the world. Were it universally adopted, the exact time at every place in the world could be determined off-hand, and without any of the calculations now necessitated by the large number of different standards.

In Universal Time the governing meridians would be 15°, 30°, 45°, &c., east and west of Greenwich, and the difference would be in hours only. Thus, if it were 10 minutes 15 seconds past I p.m. at Greenwich, it would be 10 minutes 15 seconds past 8 a.m. at New York, and 10 minutes 15 seconds past 6 p.m. at Bombay.

The International Date Line is an imaginary line marking the place where the "change of day" is supposed to occur.

By the "change of day" is meant the apparent gain of one day when travelling eastwards, or apparent loss of a day when travelling in a westerly direction.

The explanation of this imaginary gain or loss is quite simple. As 1' east or west of Greenwich makes a difference of 4 minutes between the local time of places 1o E. or 1 W. and Greenwich Mean Time, it is clear that a traveller going west and desiring to keep local time, would find it necessary to turn the hands of his watch back 4 minutes for every degree of longitude travelled over; and supposing he had started from Greenwich, by the time he had gone half-way round the world he would have set his watch back 180 times (which, at 4 minutes each time, makes 12 hours), and by the time he got back to Greenwich 180 times more, or 360 in all, i.e., (360 × 4) minutes = 24 hours, or one day. In other words, he would apparently have lost a day.

Similarly, if a person travelled east from Greenwich, for every degree of longitude passed over he would, in order to keep correct local time, be obliged to put the hands of his watch forward 4 minutes, and on returning to Greenwich, he would find that he had done the same 360 times, i.e., (360 × 4) minutes 24 hours-an apparent gain of one day.

The International Date Line, marking the place where this "change of day" is supposed to occur, passes through the Pacific from Behring Strait, southward past Japan, then curving round the Philippines, and running east of New Guinea and New Zealand. When it is Sunday west of this line, it is Saturday east of it. "Navigators, however, usually rectify the date on crossing the 18oth meridian from Greenwich, counting a day twice if the voyage is towards the west, and dropping a day if sailing eastwards."

The Determination of Latitude and Longitude is thus absolutely necessary to fix the positions and relative time of places on the earth's surface.

Determination of Longitude: As 1 of longitude makes a difference of 4 minutes in time, it is evident that longitude may be expressed in time with any required degree of accuracy, and the position of any place, with regard to the meridian of Greenwich, may be accurately determined if, by some means, the exact mean time at Greenwich, and the local time at the place of observation, could be simultaneously known and compared. For this purpose, travellers and navigators carry chronometers, or watches, set to and keeping Greenwich time very accurately. To find the longitude at any place, it is only necessary