The following text may have been generated by Optical Character Recognition, with varying degrees of accuracy. Reader beware!

32 TAE Marine REVIEW SCIENTIFIC LAKE NAVIGATION By Clarence E. Long THE MARINER'S COMPASS. oe Full Details as to Its Operation, Construction, Sys- tems of Notation. LESSON II. The mariner's compass is simply an instrument that utilizes the directive or pointing power of the magnet. Any magnetized piece of tempered steel, permitted to turn at its center of gravity (poised so that it will bal- ance), and left to the influence of the earth's magnetism, will, by magnetic attraction, point to a definite direction, known as magnetic north and south, and, from this direc- tion all other directions, by means of the compass card attached to this magnetized piece of steel, are taken and a ship guided on any desired course. - This means. that if any magnetic needle be hung at its center by a thread, so that it will balance, or poised on a pivotal bearing at its center of gravity, so as to move freely in a horizontal plane (on a level with the horizon), i will at first move to and fro (by attraction and being dis- turbed from its natural position in the magnetic meridian but will eventually come to rest (by this same attraction) in a north and south line. This line or direction, is what is called the magnetic meridian, since it is in the direction of the magnetic north pole, which varies with the true -- ©: : SPOLe Showing a ap netic needle off and on its Sport or pivotal bear- ing. The shaded portion is north magnetism or the north pole, and 'the light portion is south magnetism or the south pole. meridian or the direction of the true pole, at different places on the earth's surface. The angle this magnetic meridian (pointed out by this piece of magnetized steel -at any place, or by the north and south points of any compass card) is called. the variation of the compass. which will be fully explained in another lesson. The working principle of the compass is simply the poising of the magnetized needle of steel, so that by be- "ing permitted to turn on its axis freely, it is controlled "by the earth's magnetism and kept pointing constantly "4m;,one direction, This is practically all there is to its principle. The simple law of nature that is responsible for its power of direction, is the law. of magnetism. The earth itself is supposed to be a great natural magnet, and the attractive influence of its magnetic poles, which are 'situated some distance from the geographical poles, are supposed to give direction to the magnetic needle. The first fundamental law or principle of magnetism 'is attraction and repulsion of magnetic poles. Like poles , Tepel each other and unlike poles attract each other. : Be bs the like or same 'poles of two magnets oo one s "magnet Of: tue» eompags) - will repel or drive each Other away when. brought near to. each eather: that is, of like name, or magnetically of the same kind, as two north or two south poles. The unlike poles of any two magnets, under the same conditions, will attract each other, as the north pole of a magnet will attract the south pole of another magnet, and vice versa, Whenever attraction takes place magnetically the forces must be opposite in name. The constant pointing of the magnetic needle to the north magnetic pole of the earth depends on the two kinds of magnetism of which each is composed, one is of the south kind and the other of the north kind. The magnetism of the north magnetic - pole is composed of the south kind, and the north end of the compass needle, or other magnet bar, of the north kind; hence, being magnetically opposite, attraction is the result. The mariner's compass, although simple from a math- ematical point of view, is wonderful as a phenomena. Let us understand that it consists only of a magnetized flat bar or needle of steel riveted to a circular card on which 32 equal lines are shown radiating from the centet and indicating the various compass points of the hori- zon. This magnet with the card attached is balanced on a sharp, steel point and rests in a horizontal position, pre- serving the same when the vessel pitches and rolls, and being poised to turn freely, it always points out the magnetic cardinal directions, provided that disturbing influences in the way of iron and steel are not brought in near proximity to it. In other words, the compass card will remain fixed while the vessel revolves beneath it. The earth is a huge magnet and has a north and south magnetic pole. An iron. bar acquires polarity by mag- netism, and when freely suspended from its center of gravity (either by a thread or by being poised on a sharp point) it will arrange itself in the magnetic meridian and point to the magnetic poles of the earth. These mag- netic poles are respectively the points on the earth to- ward which the magnetic needle itself, or where it may, for the better understanding of the subject, be considered that the intensity of the magnetic force is.a maximum. The earth being a magnet its magnetism has the same properties that the magnet of the compass has. It has a north and south magnetic pole, and its laws and prin- ciples are similar to the magnet of the compass. Every magnet has two distinct poles of different mag- netism, or polarity. One of them is called a north pole and the other a south pole; that is, the magnetism is of two varieties, the north kind and the south kind, or mag- netically opposite to each other. The earth being a mag- net has a north magnetic pole and a south magnetic pole; these are distinct from the true poles at the end of the earth's axis. The north magnetic pole is situated some 1,200 miles south of the true north pole of the earth, and the south magnetic pole is some 900 miles north of the earth's true south pole. You will notice from this that these two magnetic poles are not diametrically opposite to each other, as are the true poles of the earth. The magnet (bundles of magnetized steel wires) in every compass has a north pole and a south pole, or it is com- posed of north magnetism and south magnetism. Now, every magnet has what is called an equator, or neutral line, and this line is located about midway between the two poles, or ends of the magnet. It is also called the dividing, or separating line, that is, it separates the two kinds of polarity, or magnetism, from each other. It is also called the point of magnetic indifference, meaning