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22a ——E—E—————E—————— aed THE MARINE RECORD. PRACTICAL METHOD FOR FINDING COMPASS ERRORS. ARRANGED FOR MASTERS AND PILOTS ON THE GREAT LAKES. BY JOHN ROSS, LATE MASTER LIGHT-HOUSE TENDER 9TH. DISTRICT. (Copyrighted 1897, all rights reserved.) CHAPTER VI. NAPIER’S DIAGRAM. Napier’s Diagram (see plate) affords the best means for applying compass deviations. No special. skill or aptitude is required for the laying down of the deviation NAPIER’S DIAGRAM FOR COMPASS DEVIATION. W. DEV. Ss. W. DEV. N. E. DEv. OS < PS Seip co Cae <i as oe Saas aa 4 ; Nk | = ts Eby | S20. : . 1 oe EAST (1%0 js of plain lines, these systems crossing each other at the divisions marked by the points of the compass, the dotted lines being inclined downward as they are drawn to the right. At the side of the vertical line are indicated the compass points, also the number of degrees from North to East and West, and from South to East and West. Easterly deviations are laid off to the right from the vertical line and westerly deviations to the left. If, as is shown in table 1, the deviation has been determined on the, exact points of the standard compass, to lay down the deviation curve, with a pair of dividers take off on the scale of degrees, alongside the vertical line, the number of degrees of deviation on any one of the ship’s headings, and then lay down this measured E. DEv. HOWEST’ To PLOT THE DEVIATION—Lay off the deviation on the dotted line passing through the point for which the deviation has been found, To Finp THE MaGneTic Course—From the compass course on the vertical line, measure to the curve parallel to the dotted line and return to the vertical line in a direction parallel to the plain line. To Frnp ‘THE Compass CouRSE—From the magnetic course on the vertical line, measure to the curve parallel to the plain line and xetura to the vertical line in a direction parallel to the dotted line. curve and taking off either the magnetic course or com- pass course as required. The diagram consists of one vertical line divided into 32 equal parts, each division answering for a point of the compass, or two vertical lines each divided into 16 equal parts as shown in the plate. The vertical line or lines are crossed at angles of 60 degrees by a system of dotted lines and a system distance on the dotted line passing through the point marked the same as the ship’s heading, taking care to measure the distance to the right from the vertical line if the deviation is easterly and to the left if it is westerly. Make a light pencil mark to indicate the measured dis- tance oni the dotted line. Repeat this operation for each point of the ship’s heading and when the deviations for “arms L and balls M, shaft G having disks J and K, all the points of the ship’s head have been marked, ¢ a fair curve through the marks; and the deviation curve for the standard compass is then complete. i If the deviations have not been determined on ex points of the compass, take the point on the vertical which corresponds to the ship’s head when the bear was taken, and from this point lay off the deviatio a line parallel to the dotted line. 0 OBTAIN THE MAGNETIC COURSE FOR ANY COMP: COURSE. ae On the vertical line note the given compass cour from this point with a parallel ruler lay a parallel to the dotted line as far as the curve; from thi point on the curve return to the vertical line on a line parallel to the plain line. The point arrived at on th vertical line will be the magnetic course desired. TO OBTAIN THE COMPASS COURSE FOR ANY MAGI COURSE. ; On the vertical line note the given magnetic co from this point with a parallel ruler lay a 1 parallel to the plain line as far as the curve; from t point return to the vertical line on a line parallel the dotted line. The point arrived at on the vertical J will be the compass course desired. Bearings are takem from the diagram in the same mi mer as courses. From the deviation curve a table showing the compass. course (or bearing) corresponding to the magnetic course (or bearing) for each quarter point of the compass may = be made. And also, if it be desired, a table showing the magnetic course (or bearing) that corresponds to the compass course (or bearing) for each quarter point. It will be found that a table arranged to quarter points will answer in practice, for if a course between the quar- ter points be desired it can be obtained by interpolation. When extreme accuracy is necessary, or if a vessel i steered to degrees, take the course directly from th curve. The deviation table should be kept where access to i can be had at amy time. 2 The deviation curve shown on Napier’s Diagram 7 resents the deviations in table I. (TO BE CONTINUED). ——————q-71 98. — ~ RECENT MARINE PATENTS. 575,203. Apparatus for Calming Seas by Distributin Oil Thereon. Albertus J. van Beek, Buda-Pesth, Au tria-Hungary. Filed June 20, 1896. An apparatus for the calming of seas by distributin oil, comprising an oil-reservoir having an outlet a1 means, for forcibly discharging the oil, wth electro- netic mechanism controlling the operation of the forein means. A floating buoy provided with an oil-reseryoir havi an outlet and means for forcibly discharging the oil, w electro-magnetic mechanism controlling the operation the forcing means, and an electric circuit from said electr magnetic mechanism to the shore or other distant poi A buoy provided with an oil-reservoir, an outlet for” oil therefrom, and a piston in ‘the reservoir, the said pist beng connected with a tube having a nut, in com tion with two cylinders provided with right and I handed screws, respectively, to engage with the said spiral springs in the cylinders and electric escapet gear controlling the action of the springs. a 579,204. Governor for Marine Engines. Alexander son, Hull, England. Filed Feb. 10, 1896. : An apparatus for governing marine engines to pre them racing, consisting of a large cylinder A’ and as cylinder A with piston-valves B and D and inlet and let pipes C and C’ respectively operated by mea . piston-valve of small cylinder A being operated by for working in the groove K’ of loose disk K, the w being driven by means of pulley H connected by str rope or the like to pulley on driving shaft of engine. An apparatus for preventing marine engines racin employment of a fork R having screwed end S ad by means of nut U or the like and bearing against nected disks P and P’ for compressing the spring regulating the movements of the balls M, and in nection with cylinders A and A’ with pistons and pist valves and pipes C and C’ operated by arms L and ball (CONTINUED ON PAGE IT),