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eG Sy SS SSW VY} 7 V) ° SSS oat and Ashore Gyroscopic Compass—Shipyard Cranes—Steel Ship Knees pass would point to the true geo- graphical north under all conditions, naviga- tion would be a simple problem. In reality, however, the compass points to the magnetic pole which is situated some 300 miles south of the north pole. Fur- ther to complicate the problem, the magnetic pole changes its posi- tion from year to year. This variation or error is to be found on every chart. The magnetic com- pass is also affected by ore deposits, when sail- ing on the Great Lakes for instance, magnetic mountains and _ other natural magnetic causes. Sometimes these errors are known and taken into account but often the navi- gator is ignorant of them with the re- sult that many ships have piled up on a ledge or gone ashore. On steel vessels, the compass is subjected to a further error called deviation. This error is» caused by local magnetic effects of the ship and her cargo. This deviation varies with time, latitude, character of the cargo and with changes of temperature. A still further error, called heeling error, is caused by the change in the relative position of the ship’s hull and cargo with reference to the compass. This is brought about when the ship rolls. To illustrate, if a vessel is steering due north and rolls to port, all the mag- netic material of the ship to the east- ward of the compass pulls the north pole of the compass toward it. When the ship rolls to starboard the reverse condition is brought about. Under these conditions, it is a difficult matter for the quartermaster to keep the vessel on her course. Numerous compensating means have been provided for correcting deviation and heeling error; and on merchant vessels it is customary to have an ex- pert compass adjuster come aboard periodically to correct all the deviation he can with means provided for this purpose. Then, by swinging the ship and taking observations on the: sun or some distant object, he compiles a table of the residual deviation errors remaining in the compass. This table T the magnetic com- EE” ye EI Oe ae CARD OF THE THE MASTER GYROSCOPIC COMPASS IS SHOWN IN THE UPPER ILLUSTRATION— REPEATER IS SHOWN BELOW 164 is used by the ship’s navigator in laying out his course. With the object of providing a compass that would be free of such errors under. all conditions, the Sperry Gyroscope Co., Brook- lyn, N. Y., has. deével- oped a compass which makes use of a natural principle. The compass has been employed for some years on_ vessels of American, British and other foreign navies and gave service in the naval battles of the war. In describing the magnetic compass, sci- entists teach that the earth is a large magnet and that all small mag- nets on the earth’s sur- face have a tendency to place themselves in the same direction as the large mag- net. This is why a magnetic compass points approximately north and south. The gyroscopic compass works on a somewhat similar principle. Any small revolving wheel when placed on a large revolving wheel has a tend- ency to place its axis in the same direction as the axis of the large wheel. Thus, when a small revolving wheel is placed on the surface of the earth, and suspended so that it is free to follow its natural tendencies, it will place itself in such a position that its axis is pointing in the same direction as the axis of the earth, the small wheel rotating in the same direc- tion as the earth. The gyroscope is nothing more than a rotating wheel; a discovery of the French. The principle is not new, of course, as it was incorporated in a revolving toy more than 40 years ago. Its application in a compass, however, is comparatively new. Fur- ther to explain the action of the gyroscopic compass, imagine an ob- server at a point’ in space directly above the south pole of the earth. He would at once notice the earth, turn- ing clockwise upon its axis which pointed directly toward him. Now, let it be assumed that he could also see a number of rotating wheels on the earth’s surface. The axes of these wheels would be pointed toward him and the direction of rotation would be just the same as that of the earth. Fe ee ee Se, By el TO , ; q ; | 4