The Polar Regions extend respectively from the Arctic and Antarctic circles, in 66° 32' N. and S., to the north and south poles, the circles being 1,408 geographical miles from the poles. The intense cold and the difficulties of ice navigation have made the discovery and examination of these regions a slow and hazardous task. Millions of square miles are still entirely unknown. Notwithstanding, the discovery of the North Pole by Cook and Peary, this vast area must still remain unexplored.

The Arctic circle is a ring running a little south of the northern shores of America, Asia and Europe, so that those shores form a fringe within the Polar Regions, and are its boundary to the south, except that three openings — those of the North Atlantic, of Davis Strait, and of Bering's Strait.

The width of the approach to this region by the Atlantic Ocean in its narrowest part is 660 miles, from the Norwegian Islands of Lofoten to Cape Hodgson, on the east coast of Greenland. The width of the approach by Davis Strait in the narrowest part, which is nearly on the Arctic circle, is 165 miles; and the width of Bering Strait is 45 miles. Thus out of the whole ring of 8,640 miles along which the Arctic circle passes about 900 miles is over water.

The South Polar Region, unlike the northern region, is almost covered by ocean, and the only extensive land being far to the south. It was of course entirely unknown to the ancients and to the early navigators of modern Europe, although a theory prevailed among geographers that a great continent existed around the South Pole: the "Terra Australis Incognito." It is believed that the Antarctic Regions will be very much more difficult to explore than the Arctic Regions.

The Hemisphere is one of the halves into which the earth may be supposed to be divided. It is common to speak of the Eastern Hemisphere and the Western Hemisphere, the former, also called the Old World, comprising Europe, Asia, Africa and Australia, the latter. North and South America. The boundary between the two is quite arbitrary, and a more natural division of the earth is into the North and Southern Hemisphere, the dividing line being the equator.

The Equator is the great circle of our globe every point of which is 90° from the poles. All places which are on it have invariably equal days and nights. From this circle is reckoned the latitude of places both north and south. There is also a corresponding celestial equator in the plane of the terrestrial, an imaginary great circle in the heavens the plane of which is perpendicular to the axis of the earth. It is everywhere 90° distant from the celestial poles, which coincide with the extremities of the earth's axis, supposed to be produced to meet the heavens. During the apparent yearly course the sun is twice in the celestial, and vertically over the terrestrial equator, at the beginning of spring and of autumn. Then the day and night are equal all over the earth, whence the name equinox. The magnetic equator is a line which pretty nearly coincides with the geographical equator, and at every point of which the vertical component of the earth's magnetic attraction is zero; that is to say, a dipping needle carried along the magnetic equator remains horizontal. It is hence also called the aclinic line.

Greenwich is within a few miles of London, England, and a great astronomical observatory is located there. Time in all parts of the world is measured according to meridian east or west of Greenwich. There are in all 180 meridians east and 180 meridians west of Greenwich, total 360. It is plain then that the meridians begin to number in both directions from Greenwich.

The Meridian of Greenwich extends half way around the world from the North Pole to the South Pole. Beyond the poles, however, on the opposite side of the world from that covered by the Meridian of Greenwich, it is the 180th meridian, also extending from pole to pole; the Meridian of Greenwich and the 180th meridian being the exact antipodes of each other.

Since the earth's rotation around the sun makes the sun pass 15 meridians each hour, if you will divide the total number of meridians, 360, by 15, you have 24, the number of hours in a day. Roughly speaking, the 180th meridian is midway between San Francisco and Manila. Approximately there are 160 meridians between New York City and Manila via San Francisco, so there would be 200 meridians between the two places via Europe and Asia. Divide 200 by 15 as explained above and you have the difference in time between Manila and New York, which would be 13 hours, and 20 minutes.

Latitude, in geography, the distance of any place on the globe north or south of the equator measured on its meridian. It is called north or south according as the place is on the north or south of the equator. The highest or greatest latitude is 90°, that is, at the poles; the lowest or smallest o, at the equator, between which and the poles are the parallel circles, called parallels of latitude. One method of finding the latitude of a place is by measuring the altitude of the pole-star. When the latitude and longitude of a place are given its position on a map is easily found.

One difficulty that may lie in a matter apparently so simple as the reckoning of the days of the week is well shown in one of Poe's stories. The obdurate father of the maiden — evidently with the Greek calends in mind — promises to give her to the objectionable swain when three Sundays occurred in one week. To his consternation, and the joy of the lovers, the seemingly impossible event indubitably happened when two sea-captains appeared together upon the scene who had circumnavigated the globe in opposite directions. As a matter of fact, this bit of fiction represents what is taking place every day in the year, and must continue to occur as long as our present method of reckoning time is retained. And the reason for this is simple and familiar. The civil day begins and ends at midnight, but for convenience of explanation let us assume (as in the practice of astronomers) that the day begins at noon and ends at the following noon. It is clear that the interval of time between two successive noons will be, for us, twenty-four hours (or a day as measured by one complete rotation of the earth) only when we remain on the same meridian. For if at noon on the beginning of Monday we move, say, over a space of fifteen degrees toward the east, it is obvious that when the sun again stands at noon, for us, only twenty-three hours will have lapsed, since we shall have accomplished one twenty-fourth of his journey for him; that is, Tuesday, will begin, for us, one hour too soon.

Similarly, if we repeat this eastward movement, Wednesday will begin two hours too soon; and so on, until, when our starting point is reached, we shall, in count of days, be just twenty-four hours ahead in our reckoning. The result will be that, instead of ending the journey in twenty-four days (as we seem to do) and on a Wednesday, we shall actually complete it in twenty-three days, and on Tuesday. On the other hand, if we move westward in this way the reverse will happen; our days, as measured from noon to noon, will be twenty-five hours long, and we shall actually complete the trip in twenty-five days and on Thursday. For the stay-at-home, and for travelers returning thus from the east and from the west, there will, accordingly, if no correction is made in the reckoning, be for each day three distinct dates, each perfectly correct by diary or log; and each day of the week, not Sunday simply, will be repeated thrice.

This shifting of dates is, of course, the same in the end whether the journey about the earth be made in a month or in a thousand years; and, in reality, it has become of practical interest principally in connection with movements of population which have extended through centuries. From Europe as a center the leaders of modern exploration advanced toward both the west and the east; and in their footsteps colonists have followed establishing new centers of civilization, whose commercial intercourse with Europe has in general been maintained along the routes of the earliest exodus. But the colonists carried their European dates with them; and it has thus happened that at all the points — chiefly in the islands of the Pacific Ocean — where the east-ward has met the westward current of colonization and commerce, there has arisen a conflict of dates identical with that just explained. On the one hand lies regions where the time reckoning has lagged behind; on the other, regions where it has shot ahead. An imaginary line drawn upon the surface of the globe separating the regions where this difference in dates prevails is a date-line; and it is clear that the difference of reckoning marked by each line is, in general, one day, for when two circumnavigators, starting in opposite directions from one place, meet one another in the journey, one will have lost just that part of a day which the other has not yet gained. On the eastern side of the line, namely, the date will be one day earlier than on the western side; that is, if it is Sunday on the former it will be Monday on the latter. It is characteristic, also, on such a line that if on crossing from the west a day is added to the reckoning, or on crossing it from the east a day is omitted, the shifting of the dates will be corrected. This correction is a common item in the diaries of travelers and the log-books of mariners.

The following is a complete and accurate list of the deaths among members of the parties of polar travelers: