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SHIP SHOULD BE ON AN EVEN BEAM. Bear in, mind that. when ascertaining the deviation by any of the © methdds herein laid down be sure that your vessel is beyond all magnetic influences from surrounding objects (to prevent local attraction), and that the vessel herself is equipped for the voyage, that is, any- thing that will cause an 'attraction should be in its regular place, such as boat davits, the anchor crane fore-and-aft in the mid- ship line, ventilators in their place, etc., - etc. Be sure that the vessel is: on' an even beam (to prevent heeling error en- tering the deviation). This is a very im- portant matter, for if the ship has even' a slight list the deviations will not be the same aS when on an even beam. The de- viations may be more or less when the vessel heels than when on an even beam. 'The deviation is different for a starboard list than a port list for the same 'point of the compass. For example, supposing the deviation on north was easterly with the ship on an even beam; with a star- board heel the deviation, we will say, is easterly. If this were true then the de- viation would be westerly with a heel to port. The deviation then from an even beam would be increased by a starboard list atvd decreased' by. a port list... The greater the heel the greater the heeling deviation.. It is greatest on northerly and southerly courses and least on east- erly and westerly: courses; or the heeling deviation reaches its maximum amount on north and south and its minimum on east and west. The causes and effects of heeling deviation will be more fully ex- plained in a chapter to follow. The stu- dent should remember what has been said of this heeling question, as he' will be better able to understand what is to follow. Note.--Even hon is a term employed to indicate that the ship neither heels to port nor starboard, which by the mariner is called even keel, but this last term is also used to signify that the ship draws the same depth of water fore and aft, the use of the same expression to indicate two different conditions of the ship be- ing calculated to cause confusion. Up- tight is also a term that is used to indi- cate the same thing as even beam. KEEP THE SHIP STEADY FOR SEVEN MINUTES. Therefore, the water should be smooth so that the ship's rolling will not cause heeling deviation, and also not to inter- fere with the observer in taking the bear- ings and in reading the compass. See that you have a good man at the wheel, and special care must be exercised to keep the vessel perfectly steady on each course or heading. In this work a vessel should remain on each course for at least seven minutes, and ten minutes would be petter. The object of keeping the ship steady on each heading (when getting the Dey.) for seven minutes is to allow the mag- "THE Marine REVIEW netism induced in soft iron of the ship to conform itself to, each new direction. It must be understood that whenever the ship's. head is changed in azimuth. the soft iron in the ship undergoes a change by the earth's inductive forces, which is the real cause of this iron becoming mag- netic. This stationary direction of the ship's head gives all such iron a chance to acquire its' new relations, or to go through its various magnetic phases due to a change of direction; or in other words, permits the compass card to come to rest, for sometimes this iron is harder than ordinary soft iron, and 'therefore takes a longer time to lose or ga'n mag- tetism, «. ' Note.--Not less than seven minutés on each 'heading .should be allowed, but five will-give very good results; seyen or ten is better, so there will not be so much chance for an error on account of ad- hesive attraction. HORIZONTAL AND VERTICAL SOFT IRON. Now, what must be the shape of this iron to undergo' such change--horizontal or vertical? It cannot be vertical iron because it remains in the same upright position, no matter what direction the ship's head may be in; horizontal iron, tion as the ship swings around, and 'of course, when its direction is in one with the mag- netic meridian, and least when the iron is at right angles to this meridian; in other words, when the ship's head is brought around so as to cause the ends of horizontal' iron 'to point north 'and south, or near to north and' south, the edrth's horizontal. force. makes magnets of theth. When the ends of this iron point east and west, or near to east. and west, it loses its magnetism, since its length is at right angles to the earth's horizontal force; hence, no action can take place. rection of the iron and not the direction of the shin's head. As the ends of horizontal iron approach the magnetic meridian they begin to ac- quire magnetism, and this magnetism gradually increases as the meridian is approached, reaching its maximum amount when coincident with the merid- ian. When the ends of this iron are turned away from the meridian the iron loses magnetism and it has none when it reaches east and west. Take an iroti deck beam, for instance, when the ship is heading either east or west, . correct magnetic, at any place, the deckbeam lies in the magnetic meridian, and its ends are magnets: by induction from the' earth: As the ship's head is brought towards north or south the ends of the deckbeam take the direction of east and west and its magnetism is lost. It is in' cases of this kind, when the ship is turned: quickly, and only steadied for a short time on but not so with which charges its posi- must be greatest in magnetism. Remember that it is the di- 33 each new direction, that this iron cannot either gain or part wholly with transient induced magnetism, as already explained. THE IRON DECK BEAM, Take the example of the iron deck beam again, when the ship's head is east the port end of the beam has a red pole, or one-half of it is red or north magnet- ism, since the magnetism of the' earth is blue and the magnetism by induction mttst bé opposite in name to the force that produced 'it; or the pole or end of the iron, lying next to the inducing force, must have opposite names. We know that the earth has blue magnetism, con- sequently, that end of the iron lying near- est to it must have an opposite polarity; and so it has. The'starboard end of the beam then has blue magnetism. If the » ship were heading west the starboard end of the beam would have red magnetism and its port end blue.' With the. ship in either of these directions the iron beam is strongest in magnetism, since -its length lies in the magnetic meridian, and gets' the full phen: of the inducing force. - With the ship's head on any heading north or south of east, the port end of the beam retains its red magnetism, but its force of power weakens gradually as the meridian is approached and it van- ishes entirely on the meridian. On headings north or south of west the starboard end of the beam has red mag- netism, but its intensity depends on the angle it makes with the meridian. The smaller this angle the stronger this force, and the greater this angle the weaker the magnetism of the deck beam. It must be understood that when one end has blue magnetism the other end must have red magnetism. Remember, that it is soft iron that we are talking about. ~-- WHEN THE DIRECTIVE FORCE IS WEAK. © On some headings where the directive force is weak, a longer time than seven minutes may be required for the soft iron of the ship to lose or gain its mag- netism, or for the compass card to come to rest. Where it occurs that the di- rective force of the compass is weak is on those courses which are on and: near to the direction of the ship's head in building; in other words, the magnetic force of the ship is then in direct an- tagonism to the earth's: directive force, which is supposed to control the action of the compass needles carrying the card: If it were only the earth's magnetism that had influence on it, there could be no deviation, since the directive force on the compass would be the same for all courses of the ship. Where the di- rective force of the ship and earth are combined, the force being greater the result causes deviation; where they are in opposition, the ship's force being greater than the earth's: force the result is. deviation. ons