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28 ANNOUNCEMENT. IT IS SUGGESTED' THAT MASTERS AND MATES, WHEELSMEN AND WATCHMEN AND OILERS AND WATERTENDERS WHO ARE COMPETING IN THE QUESTION COURSES NOW RUNNING IN THE MARINE REVIEW, KEEP DUPLICATES OF 'LIST OF THEIR ANSWERS. AS THE COURSE WILL RUN FOR SEVERAL' MONTHS YET, COMPETITORS MAY, if THEY: DISCOVER. "THAT THEY. HAVE On eet ERLY VARIAtTy ah TAE Marine REVIEW . By Clarence E. Long It is impossible to obtain a magnet with only one pole. If a magnetized needle is broxen into a number of small pieces, each little piece is a magnet having a north-seeking and a south- seeking pole. Hence it would appear * that. every particle of a. magnetized body! is a little «magnet, all having their south-seeking poles set in one SCIENTIFIC LAKE NAVIGATION | ® sf bismuth, antimony, copper, silver, gold, lead, sulphur, phosphorus, and water, are not only not attracted by a magnet, but are actually repelled; these are said to be diamagnetic. When a magnet substance is brought near to or in contact with a magnet, it becomes converted into a magnet 'by magnetic induction, just as a The two illustrations above show the relation of the magnetic. and true polés of the earth;and the isogonic lines, or lines of equal variation, with the true meridians.. The heavy,. irregular lines converging to, and passing through the magnetic poles, are the equal 'lines of variation, 'technically known as isogonic lines. They are in one sense nothing more 'than magnetic meridians,:'for- each line or ANSWERED INCORRECTLY, SEND IN Appi-. direction, and their north-seeking , change is induced in a conductor by TIONAL ANSWERS. BY KEEPING A DUPLI-_ poles in the opposite direct.on. There- an electrified body. The nearest pole curve indicates that along any such line the variation needle is of the same amount. .Isogonic lines, or lines of equal. variation, do not indicate. by their direction the direction of a freely swinging magnetic needle under the influnce of terrestial magnetism only. For this reason this system of indicating the variation needle is ill adapted to carry a distinct view: of .the phenomena in themselves, or to ex- hibit their physical relations. 'To the beginner these lines. are. not:only confusing but misleading, unless he first thoroughly understands the principle and meaning of such a line. The trouble lies in getting the direction of the line'as the direction of the needle, instead of the line indicating that the variation is of the same amount all along the'same line, or for all locations situated on such a line. There is no telling how much the variation is by the direction of an isogonic line; each line must have the amount inscribed alongside of it, such as 10° E, 20° W, etc., before anything can be told about it. : ; ae The isogonic lines, or lines of equal variation, in the above illustrations are not a true representation of the real isogonic lines of the earth, they mérely show the principle of the system of marking the variation where it is of the same amount; they also show ™ how irregular the variation of the compass is compared with the true directions; how the variation can be the same at certain places and of different amounts at other places, also the manner in which the magnetic needle points to the magnetic poles of the earth and not to the true poles; why the variation: is easterly at some portions of the earth and westerly at other' portions. It is: easily noted that when the observer is so situated on the earth's surface as' to. bring the north magnetic pole to the right of the true north-pole the va- riation is easterly (see first illustration), and when in such a position as to bring the north magnetic pole to the 'left of the true north pole, the variation is westerly. Also, when in such a position as to bring both the true and. magnetic north poles in~transit . with each other, the variation is nothing. While these illustrations do not accurately show the system of isogonic lines as they are on the earth's surface, they,' nevertheless, afford 'the student a correct and distinct view of all the phenomena connected with the system called isogionics. ie The system of isogonic lines connecting the north and south magnetic poles with almost the same regularity as the geographical me- ridians converge to the geographical poles is not a fact. We have made them so in order to simplify matters, in connection with the study. As a matter of fact there is absolutely no intersection of the isogonic. lines at these poles from points at any considerable distance. True, they converge to the magnetic poles, but they do not intersect, the nearest intersection being about 200 miles:and the farthest about 2,000 miles away. Since all compass action ceases near the magnetic poles the impossibility of tracing such lines to the poles. Between the magnetic pole and true north pole next to nothing is known, since its territory has never been explored. CATE LIST OF ANSWERS, THEY WILL KNOW WHAT THEIR FIRST ANSWER WAS, THIS SUGGESTION IS MADE BECAUSE IT IS NATU- RAL THAT STUDENTS WHO ARE FOLLOWING MR, LONGS LESSONS MAY FIND. THAT QUESTIONS ANSWERED BY THEM SOME MONTHS PREVIOUSLY HAD BEEN ANSWERED INCORRECTLY. SUBSCRIBERS SHOULD ALSO UNDERSTAND -THAT MR, LONG IS ANXIOUS AT ALL TIMES TO ASSIST THEM EITHER PERSONALLY OR THROUGH THE PAPER, IF AT ANY TIME ANY PHASE OF THE LESSON IS NOT CLEAR TO. THEM, fore, one, face of the broken magnet must be positive, and the other nega- tive, ot magnetically opposite. Bodies may divided into two classes: viz, magnetic bodies, which are' at- tracted by magnets, and non-magnetic bodies, which are not attracted. The most magnetic bodies are the metals, iron, nickel and 'cobali Some other metals,' salts of iron, and of other metals, porcelain, paper, oxygen -gas and ozone, are feebly magnetic. Other substances} as, for example, thus indttced is.a dissimilar pole to the inducing pole, and the attraction of: the magnet is thus due to the ac- tion already described of two dissimi- lar poles. When the inducing magnet is removed, most substances lose their magnetism, and hence are said to be temporarily magnetic; the. perfection of this property in soft iron is of great importance to magneto-electric and dynamo-electric machines, which de- pend entirely for their effects upon rapid reversals of magnetic polarity. {