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32 4 - large _ ginal of the magnet. 'dles attached to large cards. * the more accurately it points; the larger the card the more accurately it is read. This is still true, so far as the length . of the needles is concérned, but not so with the size of the card. In late years | the above law has been slightly modified, and from it better and more favorable results obtained by the use of short nee- By this ar- the advantages of a J catd, . having. . large divisions tosteer. by, are secured without the drawback of long needles, which are objectionable for more reasons than have already been given. This law was founded upon a peculiarity of magnetism. It is a fact that magnetism resides principally in the sur- face, and is greatest at the ends or poles According to this, then, there is no loss of magnetic force con- sequent on thinness, as it is principally on the surface where this force resides. _ Therefore, the more surface you have the greater and wider the magnetic field, rangement and the more ends or poles the greater the magnetic power. The two together are essential requirements of a - first-class navigating compass. To illustrate these principles more forc- ibly, we will take two pieces of steel of "equal dimensions, say 6 in, long by % in. wide and 1-16 of an inch thick. We will leave one as it is and the other we will cut up into eight slender bars, each 1-16. of an inch in width and thickness and 6 in. in length. Temper and magnetize all alike, and to one not familiar with the.laws of magnetism there would seem to be the same. amount of magnetic force in the one large piece as there is in the eight pieces put together. But, is there? No, there cannot be, because in the eight pieces we have more surface and more ends than in the one single piece, and this is where the magnetism is greatest. It is a fact that the eight slender pieces will possess several times more magne- tism than the one large single piece. .Compass manufacturers took advantage of this law and are now making compasses accordingly. The eight pieces have the ° same weight as the one piece, but the eight pieces possess a greater amount of magnetic force. So from this you can readily see that it would be possible to get the same amount of directive force from several of the slender. magnets, used in conjunction with each other, with' less weight, than with the large single magnet. alone; also a wider magnetic field | would be possible, because with the sev- eral magnets it is possible to distribute them equally over the plane of the com- pass card, whereas this would be im- possible to do with the single magnet. From this it follows that in all compasses the needles should be very thin, and that there should be a plurality of them-- the less weight the less friction. The mar--- 'vessel, 'compass out fully two points. TAeE MARINE REVIEW weight of a plurality of magnets is now equally distributed underneath the sur- face of the card, which could not be done by the use of a single magnet. Compasses constructed according to the above principle could be used to ad- vantage if the size were increased from 9 in. to 12 and' 15 in. 'Some compass makers claim that there isno advan- tage gained in diameters Over Ooi. The shorter the compass needles the better, so long as they are able to do their work. There is, of course, a limit 'to the length of the needles, correspond- ing to the diameter of the card. It would necessitate that a direct proportion exist ' between the two. In most lake steamers the steering com- pass sits in its box on a wooden shelf, or stand, near the steering wheel. On one side there is a sliding binnacle lamp, to which is attached a brass or copper fun- nel to throw a ray of light on the lub- ber point of the compass, which enables the wheelsman to steer in the night time. By this arrangement the light only shines on the point to be steered, and not all over the face of the compass: If the light were so fitted as to show all over the compass it would prevent the wheels- man from seeing out ahead of him. MOUNTING THE 'STEERING COMPASS, Steering compasses should be placed according to the requirements of the and as much consideration as possible should be given to lessen the iron near the compass. All stands for the engine room indicators and bell or whistle pulls, as well as tubes or cast- ings in which they work, should not be of iron, but of brass, and if there be- a steam coil in the pilot house the tub- ing should be of brass or copper (there is never any magnetic attraction in brass or copper, i e., neither of them have any influence on the compass needle). It is also very important that sash-weights for windows should not be of iron. (It - is most likely that some of our readers have had experience with iron window weights influencing the compass, if so, they will be able to appreciate the state- ment just made.) We know of cases where these weights have drawn the Many boats have done away with these sash-weights altogether, and are better for it. The steering compass should always, if possible, be mounted on the amidship fore-and-aft line of the vessel, at a neu- tral point as far as circumstances will adinit, and with its lubber's point M47 the fore-and-aft line. He the. compass is. not' -'mount- ed so that an imaginary dine drawn through the pivot and the lubber's point will be parallel to the line of the ves- sel's keel, the steering will not be cor- rect. Where there is more than one lubber point, as in a majority of cases, an imaginary line drawn through tuc-: fore-and-aft marks will amount to the same thing. Where, from inconvenience, it is nec- -- essary to place this compass on one side or the other, as is often the case where the steam steerer is in the pilot house, or where the hand-power steering wheel is large, the error due to what is tech- nically known as parallax (looking at the. compass in an oblique direction) causes an apparent change in the relative positions of the lubber's line and the marginal divisions of the card, amounts to a marked consideration, and often - leads to disaster. The greater the space between the edge of the card and the side of the bowl, the greater this error will be. Unless the wheelsman can get the center of the card and lubber-point in one with his course, he is sure to steer to one side of it. This parallactic dis- placement of the Iubber-line frequently amounts to as much as a quarter of a point. In the run from Chicago to Pt. Betsey (203 miles) this would make a difference of 10 miles at the end of the course, a serious consideration in thick weather. It is of the utmost importance to have the steering compass directly facing the man at:the wheel, and as far distant from him as may be compatible with dis- tinct vision. The diameter, then, of such a compass in large vessels ought not to be less than 9 in. If constructed on the short-needled principle, there would' » be a great advantage in increasing the size from Io to 12 in, if not more. The steering compass should be placed as far for'ard as possible, especially so if there: be any iron in the make up of the steam steering gear, all of which is powerfully magnetic. This is also true of sailing vessels where the compass is often placed within a foot or so of the iron spindle of the steering apparatus, and it is usually: in about the same plane. By placing the compass as far for'ard as possible, it is less within the influence of the iron spin- dle, tiller, rudder-head and stern-post. The compass needle should be at least 3% feet from the iron deck beams and as much higher as can be made conven- ient to the wheelsman, always avoiding vertical iron as much as possible. The reasons assigned for mounting the com- pass as hereinbefore described will be hereafter fully explained in the Deviation of the Compass, and in the subject of Magnetism, at which time the student will be sufficiently advanced to appre- ciate the logic for such reasons. The steering compass should be sub- stantially mounted, and securely fastened in the place selected for it. The best "rig" for this is a four-sided wooden box or stand, a little larger in width than the compass box itself. This stand