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taken from the chart, gives the master the means of obtaining the deviations required for the curve. Our subscribers in practical lake service can practice, prove and estab- lish the correctness of the various statements given in the foregoing by working the following practical prob- lems taken from some of the ranges in the Soo river. Just try these and see what a simple thing it is to find the deviation; it will help you to un- derstand other problems of the devi- ation of the compass which are more difficult. Be sure to allow for the variation of the compass. Make a record of the deviation on these vari- ous headings and write them in the log- book, and then the next course you de- sire to make good, first find the, true course from the chart; second, find the variation (which you get from the chart) at departure and the variation at destj- nation, add them together and divide by 2. This half sum is the mean variation between the ends of the course to be sailed, and should be applied to the true course to obtain the correct: magnetic course. Next find from the record of the deviations the amount of the devia- tion for this correct magnetic course, and apply it to this correct magnetic course to get the compass course. Now steer this course and see what a nice hit you will make of it. You will not be steering by guess nor by God, and you will be surprised at its simplicity, and, too, when the shipmaster once under- stands. the 'theory and practice of this deviation problem and sees its effect on the compass his respect and confidence in this valuable instrument will be vastly -- increased. The following problems will explain the foregoing statements: Frying Pan and Pipe Islands ey houses in range--true bearing N 3% W Var. 41%4° Wly = %-pt., making the cor- rect magnetic bearing of the range to be north. .When your vessel's -head is brought in one with these lighthouses and there is no deviation the compass will show the same reading as that of the correct magnetic bearing of the range, which in this case is north. Supposing that when the vessel's head 'is brought in range with the lighthouses and "she is steady on the course," the compass reads something east of north, say N_% E, what is the amount and name of the deviation, that is, which way is the compass card pulled by the attraction? It must be pulled %4-pt, to the left (Wly.) deviation), because N 1%4 E is where north ought to be: Now prove this by the various rules stated: Ist. To name the deviation: If the correct magnetic bearing is to the left of the compass bearing the de- viation is westerly. North in this case \ TAE Marine. REVIEW is the correct magnetic bearing and N | % E is the compass bearing, since it is the reading shown by the compass. Now, it is easily to be seen that north is to the left of N % E by the amount of %4- pt. Hence we have established the fact that there is + %-pt. Wly. deviation when heading north by our compass and to 'steer correct magnetic north at any. place we must steer N % E by compass. Remember, 'that it is not the true course but the correct magnetic course, the true course corrected. for variation. 2d. To find the correct magnetic bearing. when the compass bearing is given, allow Wly. Dev. to the left of the compass bearing... In thiss,case. the compass "bearing is N % E, Dev. %4-pt. Wly..and %4-pt. to theleft of N % E is north, whch is another proof. 3d. To fird the compass course from the correct magnetic course, allow Wly. Dev. to the right of the correct. mag- netic course to obtain the compass - course; hence, %4-pt. to the right: of north is N &% E. Now, supposing that when the ves- sel's head is in range with the light-' houses the compass reads to the west of: north, 'say N 34. W what is ihe amount and name of the Deviation? Ans. 34-pt. Ely., the compass card being pulled to the right of its proper position, or it must have swung to the right in order to bring N "34 W where north ought to be; or when the correct magnetic bearing (north in this case) is to the right of the compass bearing (N 34 W in this, case) the .Dey..is. Ely. rom correct magnetic to compass allow Ely. Dev. to the right of the compass course or bearing; hence 34-pt. to the right of N 3% W, the compass course, is north, the correct magnetic. course. Remem- ber, that if the compass reading is to the right of what you know the correct mag- netic bearing to be the Dev. is Ely. by © -the amount of the difference. between the correct magnetic and compass bear- ings; and when the compass reading is to the left of the correct magnetic bear- ing the Dev. is Wly. by the amount of this difference. Bear in mind that Right and Easterly have one and the same meaning with reference to the compass card, and that Left and Westerly are the same. Winter Pt. Range with Mud Lake Beacon, true bearing NW % W, Var. 4° Wly = %- "pte; making the correct mag- netic bearing to be NW.~ In other words if your compass. was correct on NW it would say so when you were heading di- rectly on them, If, when on with this range the compass shows anything north of NW the Dev. is Wly. by the amount of this difference; if anything west of NW the Dey. is Ely. Remember, that when you have once found the deviation for any course it is 31 good for that course at all times 'after- wards, provided however, that there was nothing in the cargo that would influ- ence the needle, nor that the ship's mag- netism had not changed its lines of force, in relation to the compass needle from either being loaded or light or other-. wise. The deviation found will be for that particular trim of the boat, so that it becomes necessary to have at least two curves, one for when loaded and other for when light. Harwood Pt. range will give you the Same thing as Frying Pan and Pipe Is- lands." The true bearing of Harwood tange is N 314° W, Var. 4° Wly = 3- pL, Nearly, making the correct magnetic bearing north. This is an excellent po- sition to get the deviation on north, and also for adjusting the compass for this direction, since you can get the Dark Hole range over stern and be doubly sure of heading accurately. _~ Vidal Shoal Channel Range (Soo Ca- nal Ranges) over stern, the true bear- ing of which is wsw yy W (W by S°94"'S) Var. 214° Wy. = Y4-pt., mak- ing the correct magnetic bearing of the range to be W by S. With this range directly over stern the compass should read W by S if there is no deviation. If it should read west of W by S the Dev. is Wly; if south of W by S the Dev. is Ely., the amount depending on the difference of what the compass shows -- and W by S. Pt. au Pins Range, true bearing of which is SW 3% W, Var. 2%4° Wly. = %4-pt., which makes the correct magnetic bearing SW by W. If your compass reads anything to the west of SW by W the deviation is westerly; if south of SW by W, it is easterly. If the com- pass should read SW by W itself there is no deviation and the compass bear- ing is also the correct magnetic bearing. We have now found the deviation on the following correct magnetic points: North, NW,:W by S and SW x W. Turn the deviation corresponding to these points, which is expressed in frac- tional points, into degrees. For exam- ple, supposing that for North you found the Dev. to be 3% of a point westerly. _This would be equal to 4°. Now, from the deviation on the four points. thus found we can find the deviation on any point between these points by the use of Baxter's Compass Diagram. Take the number of degrees of the deviation and lay them off on the horizontal line of the diagram abreast of the compass point for which it was found, and mark it with a dot or small circle. Easterly deviations to the right of the "mag- - 9 netic line,' and westerly deviation to the left of this magnetic line, which repre- sents the zero or starting point, also the line of no deviation. For example, on North the deviation, we will say, is