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32 THe Marine REVIEW SCIENTIFIC LAKE NAVIGATION It will be seen from. the foregoing table of deviations that the zero or neutral line of the ship's magnetism coincides with the correct magnetic points N%4W_ and SME, very nearly, for this particular compass. neutral line would also show approxi- mately the direction of the ship's head at the time of building. When a compass is so placed.as to. be free from the mag- netic effects of vertical iron, and the iron used in equipping .the ship, such as the engines, boilers, smokestacks, steel masts, steam-steerer, etc., and only influenced by the magnetism in. the hull of the ship, which magnetism is acquired while the ship is building from the earth's induc- tive force, etc., it would be possible, by comparing the natural deviation on the north and south points with that on the east and west points, to determine pretty accurately the direction of the ship's head at the time of building. But in the way iron and steel is used in the construction of boats. nowadays these conditions are seldom met with; nevertheless, there is a line of no deviation for any position that the compass may be placed in on board. It must be of necessity, for the Dey. in changing name, from Ely to Wly, or. vice versa, must take place on this Hine... This line must not be confused with the true neutral line of the ship's mag- netism, Such a point, or line, exists in every hull, but it may be a most danger- ous position for the compass, owing to the closeness of the boiler, or the engine, or some other of the shin's equipment. The behavior or action, of the compass on this. true neutral line is much differ- ent from its action on the so-called neu- tral. line. deviation is usually small; is uniform, that is, the deviation increases and de- creases gradually and systematically. earth's magnetism retains its action or control, on the compass, a good deal the samme as it would when free from the ship's magnetism. With the compass. in this neutral position, and the ship's head in the direction.that her head lay while. building, there will be no deviation. The ship's head can be turned in azimuth on either side of this, for a point or 50, affecting the deviation but slightly. -In the case of the. so-called neutral line, (the line. where the deviation changes name), were the ship's head to be turned aside from this a degree or two the com- pass might go spinning, or the compass ' card would: make it appear that the ship's head itself, had turned in azimuth some 10 or 12 degrees, whereas: it-might. have been only two or three degrees, This is Under certain condit'ons this. to it. On the true neutral line the' The By Clarence E. Long due to the fickle aad variable effects of masses of iron too close. to the compass, such as the steam. steerer, for instance. This unsteady or fickle condition is due to each separate or individual part of the machine having magnetism of its. own, such as the frame, the gearing, the shaft- ing, the pinions, the pistons, the connect- ing rods, the cranks, etc. The magnetism of each piece is not stable or fixed in amount, neither do its magnetic poles lie diametrically opposite each other, or at the ends of a straight line; for example: take any individual piece of the machine which is larger at one end than at the other; it will not have its magnetic poles. in line. They will, though not necessar- ily, be. at its extremities. Imagine, some (iron) casting that is very irregular in shape, with crooks, twists and bends, with one of its ends far from a straight line to its other end; or a-casting hav- ing several legs.- Imagine magnetic poles at. the extremities of these points and the irregular and unnatural effect it would have on the compass placed near Even were these parts of the same size and thickness all the way through, their poles are not necessarily in the same straight line, nor will they neces- sarily be of the same strength. There will be consequent poles (poles lying between the neutral point and the poles at the extremities of the mass). These effects may be due to.the condi- tions of the iron or steel, its quality, strength and purity. The quality of..the iron is never the same all the way through, either as to temper or strength. Neither will it acquire nor develop mag- netism equally or uniformly over its sur- face, It is the law of magnetism that its poles are at the extremities of its mass; while this. is true it is not a: fact that they are the only poles of the mass nor the strongest of the mass. If it hap- pens that a better quality of iron, as. to purity, and of a greater temper, lie in- side of these points, they will develop a stronger magnetism than that at the ends. Tt is a well-known fact that in work- ing iron, such as welding two pieces to- gether, and even in its manufacture, hol- low places or flaws occur, with merely an outside skin over the defective parts, It is.easy, to see how it is possible for a mass of pure metal to become separated from the rest, or the impure from the pure, or the intermingling of the whole, so, that the entire mass is unequal as to solidity, purity, strength and _ temper. This being a fact its magnetic character must. likewise be unequal and at var.ance with well-established laws. This is only apparent since the laws of nature are cor- rect. It depends entirely upon the condi- tion of the substance by which the test is either made or from which it is de- veloped. a : It can readily be seen when all these individual pieces having magnetism of their own are embodied, that their effects on the compass needle as the ship swings around in a circle are abnormal and at variance with the laws of the: science. Such a combination of forces, with no uniformity or regularity of action, renders the compass useless for all purposes until adjusted. Even then the most scientific | methods of compass compensation are unable to cope with it so far as to over- come it wholly, or even nearly so. The compounded results from such inhar- monious sources are antagonistic to all laws of reason, and the disturbing forces thus produced are of an embarrassing amount and even after adjustment large errors obstinately remain. 'This fickle condition of affairs gives sluggishness to the compass in some cases, and in other cases increases the compass action to such a degree as to make it wholly un-: reliable. .In the one case,.the, earth's and ship's magnetisms are in antagonism, and in the other case are in unity. The effects of friction on the compass are ' decreased in the one case and increased in the other. Other complicated dis- turbing forces are produced, which are only .detected from observations com- pared with the ship's head in certain di- rections. THE MANY RIVER RANGES. From the preceding examples and_ tab- les, which show how to form a complete deviation table, it must at once appeal to the student that with the unlimited means. existing all over the lakes for the performance of this work, there is little or no excuse for a man sailing a boat for not having a pretty accurate deviation table... Take. for instance, the -- correct magnetic bearings of the various ranges in the St. Mary's river, Detroit and: St, Clair rivers, Lake St. ..Clair, at the en- trance to the,many harbors, and along the shores of the various lakes. These ranges form an easy method of ascer- taining the deviations, and they should be employed while in the passage up and down the lakes to form correct deviation tables for each compass on board as well as to verify and correct the old tables of deviations. Be sure to write down each bearing as you take it, and do not trust to your memory for it. There is nothing like having things down in black and white, whether it be deviation, or a man's promise,