POLES

, in Astronomy, the extremities of the axis upon which the whole sphere of the world revolves; or the points on the surface of the sphere through which the axis passes. These are on every side at the distance of a quadrant, or 90°, from every point of the equinoctial, and are called, by way of eminence, the poles of the world. That which is visible to us in Europe, or raised above our horizon, is called the Arctic or North Pole; and its opposite one, the Antarctic or South Pole.

, in Geography, are the extremities of the earth's axis; or the points on the surface of the earth through which the axis passes. Of which, that elevated above our horizon is called the Arctic or North Pole; and the opposite one, the Antarctic or South Pole.

In consequence of the situation of the Poles, with the inclination of the earth's axis, and its parallelism during the annual motion of our globe round the sun, the Poles have only one day and one night throughout the year, each being half a year in length. And because of the obliquity with which the rays of the sun fall upon the polar regions, and the great length of the night in the winter season, it is commonly supposed the cold is so intense, that those parts of the globe which lie near the Poles have never been fully explored, though the attempt has been repeatedly made by the most celebrated navigators. And yet Dr. Halley was of opinion, that the solstitial day, at the Pole, is as hot as at the equator when the sun is in the zenith; because all the 24 hours of that day under the Pole the sun-beams are inclined to the horizon in an angle of 23° 28′; whereas at the equator, though the sun becomes vertical, yet he shines no more than 12 hours, being absent the other 12 hours: and besides, that during 3 hours 8 minutes of the 12 hours which he is above the horizon there, he is not so much elevated as at the Pole. Experience however seems to shew that this opinion and reasoning of Dr. Halley are not well founded: for in all the parts of the earth that we know, the middle of summer is always the less hot the farther the place is from the equator, or the nearer it is to the Pole.

The great object for which navigators have ventured themselves in the frozen seas about the north pole, was to find out a more quick and ready passage to the East Indies. And this has been attempted three several ways: one by coasting along the northern parts of Europe and Asia, called the north-east passage; another, by sailing round the northern part of the American continent, called the north-west passage; and the third, by sailing directly over the pole itself.

The possibility of succeeding in the north-east was for a long time believed; and in the last century many navigators, particularly the Hollanders, attempted it with great fortitude and perseverance. But it was always found impossible to surmount the obstacles which nature had thrown in the way; and subsequent attempts have in a manner demonstrated the impossibility of ever sailing eastward along the northern coast of Asia. The reason of this impossibility is, that in proportion to the extent of land, the cold is always greater in winter, and vice versa. This is the case even in temperate climates; but much more so in those frozen regions when the sun's influence, even in summer, is but small. Hence, as the continent of Asia extends a vast way from west to east, and has besides the continent of Europe joined to it on the west, it follows, that about the middle part of that tract of land the cold should be greater than any where else. Experience has determined this to be fact; and it now appears, that about the middle of the northern part of Asia, the ice never thaws; neither have even the hardy Russians and Siberians themselves been able to overcome the difficulties they meet with in that part of their voyages.

With regard to the north-west passage, the same difficulties occur as in the other. According to Captain Cook's voyage, it appears that if there is any strait| which divides the continent of America into two, it must lie in a higher latitude than 70°, and consequently be perpetually frozen up. And therefore if a northwest passage can be found, it must be by sailing round the whole American continent, instead of seeking a passage through it, which some have supposed to exist in the bottom of Baffin's Bay. But the extent of the American continent to the northward is yet unknown; and there is a possibility of its being joined to that part of Asia between the Piasida and Chatanga, which has never yet been circumnavigated. Indeed a rumour has lately gone abroad of some remarkable inlet being observed on the western coast of North America, which it is guessed may possibly lead to some communication with the eastern side, by the lakes, or a passage into Hudson's Bay: but there seems little or no probability of any success this way, in which many fruitless attempts have been made at various times. It remains therefore to consider, whether there is any probability of attaining the wished-for passage by sailing directly north, between the eastern and western continents.

The late celebrated mathematician, Mr. Maclaurin, was so fully persuaded of the practicability of passing by this way to the South and Indian seas, that he used to say, if his other avocations would permit, he would undertake the voyage of trial, even at his own expence.

The practicability of this method, which would lead directly to the Pole itself, has also been ingeniously supported by Mr. Daines Barrington, in some tracts published in the years 1775 and 1776, in consequence of the unsuccessful attempt made by captain Phipps in the year 1773, to reach a higher northern latitude than 81°. Mr. Barrington instances a great number of navigators who have reached very high northern latitudes; nay, some who have been at the Pole itself, or gone beyond it. From all which he concludes, that if the voyage be attempted at a proper time of the year, there would not be any great difficulty in reaching the Pole. Those vast pieces of ice which commonly obstruct the navigators, he thinks, proceed from the mouths of the great Asiatic rivers which run northward into the frozen ocean, and are driven eastward and westward by the currents. But, though we should suppose them to come directly from the Pole, still our author thinks that this affords an undeniable proof that the Pole itself is sree from ice; because, when the pieces leave it, and come to the southward, it is impossible that they can at the same time accumulate at the Pole.

The Altitude or Elevation of the Pole, is an arch of the meridian intercepted between the Pole and the horizon of any places, and is equal to the latitude of the place.

To observe the Altitude of the Pole. With a quadrant, observe both the greatest and least meridian altitude of the Pole star. Then half the sum of the two altitudes, will be the height of the Pole, or the latitude of the place; and half the difference of the same will be the distance of the star from the Pole. But, for accuracy, the observed altitudes should be corrected on account of refraction, before their sum or difference is taken. See Refraction.

, in Spherics, or the Pole of a great circle, is a point upon the sphere equally distant srom every part of the circumference of the great circle; or a point 90° distant from the circumference in any part of it.— The zenith and nadir are the Poles of the horizon; and the Poles of the equator are the same with those of the sphere or globe.

, in Magnetics, are two points in a loadstone, corresponding to the Poles of the world; one pointing to the north, and the other to the south.

If the stone be broken in ever so many pieces, every fragment will still have its two Poles. And if a magnet be bisected by a plane perpendicular to the axis; the two points before joined will become opposite Poles, one in each segment.

To touch a needle, &c, with a magnet, that part intended for the north end is touched with the south Pole of the magnet; and that intended for the south end, with the north Pole; for the Poles of the needle become contrary to those of the magnet.

A piece of iron acquires a polarity by only holding it upright; though its Poles are not fixed, but shift, and are inverted as the iron is. Fire destroys all fixed Poles; but it strengthens the mutable ones.

Dr. Gilbert says, the end of a rod being heated, and left to cool pointing northward, it becomes a sixed north Pole; if southward, a fixed south Pole. When the end is cooled, held downward, it acquires rather more magnetism than if cooled horizontally towards the north. But the best way is to cool it a little inclined to the north. Repeating the operations of heating and cooling does not increase the effect.

Dr. Power says, if a rod be held northwards, and the north end be hammered in that position, it will become a fixed north Pole; and contrarily if the south end be hammered. The heavier the blows are, cæteris paribus, the stronger will the magnetism be; and a few hard blows have as much effect as a great number. And what is said of hammering, is to be likewise understood of filing, grinding, sawing, &c; nay, a gentle rubbing, when long continued, will produce Poles.

Old punches and drills have all fixed north poles; because they are almost constantly used downwards. New drills have either mutable Poles, or weak north ones. Drilling with such a one southward horizontally, it is a chance if you produce a fixed south Pole; much less if you drill south downwards; but by drilling south upwards, you always make a fixed south Pole.

Mr. Ballard says, that in 6 or 7 drills, made in his presence, the bit of each became a north Pole, merely by hardening.

A weak fixed Pole may degenerate into a mutable one in a day, or even in a few minutes, by holding it in a position contrary to its pole. The loadstone itself will not make a fixed Pole in every piece of iron: if the iron be thick, it is necessary that it have some considerable length.

Pole of a Glass, in Optics, is the thickest part of a convex glass, or the thinnest part of a concave one; being the same as what is otherwise called the vertex of the glass; and which, when truly ground, is exactly in the middle of its surface.

, or Rod, in Surveying, is a lineal measure containing 5 1/2 yards, or 16 1/2 feet.—The square of it is called a square Pole; but more usually a perch, or a rod.|

Pole-Star, is a star of the 2d magnitude near the north Pole, in the end of the tail of Ursa Minor, or the Little Bear. Its mean place in the heavens for the beginning of 1790, was as follows: viz,

The nearness of this star to the Pole, on which account it is always above the horizon in these northern latitudes, makes it very useful in Navigation, &c, for determining the meridian line, the elevation of Pole, and consequently the latitude of the place, &c.