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30° should sight through the eye-piece (peep-hole) of the azimuth attach- ment, keeping the hair sight on the back range, moving it slowly and evenly, as the vessel lessens the an- gle; then at the instant that the ob- jects are in range (as seen through eye-piece) read the bearing in de- DEVIATION TABLE I. THE MaRINE REVIEW yourself. Order the helm to port or starboard till the. ship is precisely on the course or point of the compass you desire by standard. At that in- stant -the man at the wheel notes the direction by his compass and steadies the ship's head to it: After a few min- utes compare the two courses again . center mark of the azimuth instru- ment coincides with a division on the compass). THE VALUE OF USING THE PELORUS. If a pelorus is used [this is the in- strument best adapted for all purposes of this kind] the reading can be taken any time after the vessel has crossed the range, so long as it was set to the range carefully, and not moved a particle from that time until the bear- ing is read off, and for this reason it is much more convenient than any TABLE II. Ship's Head Deviation in | Ship's Head by Compass. Degrees. Correct Mag. North 12° Wly NE 122 WwW, N by E Tes Ne 42 And so on with every point of the compass other instrument. Clamp the pelorus dial to the course the ship is steering on and where the sight vanes cut the object, read off, the difference between ' this and what you know the correct magnetic bearing to be will be the amount of the deviation for the com- pass course steered. It is advisable to have a person (one of the officers) stationed near the standard compass to. steady the _wheelsman, so as to leave the observer free to attend to the observations. TO SET THE COURSE BY STANDARD COM- PASS. the standard Stand by compass ed. Col, 2. Col. 3. Col. 4. Col._5. Ship's Head Bearing of Correct Mag. Deviation. Ship's Head by Compass. Chimney by 'Bearing of Correct Mag. ~ Compass. © Chimney. : NODE. Fair Oe epee s N 70° W N 82° W 12° Wy. N« 12° WW: INN ee ors eee ees N75 W e 7 . N 4._E INN eee lacie N 80 W : 3 2 N 2b7 8 Pets 3... N85 W «" 3. Ely N37 E Ue oe ee cess N 89 W s ZB 2 N52 ON EY Bye Be cee cess N 92 W sf 1g N 66 E TONGS a cee eyes 6s 2 ae ss N95 W : 1B oe N 8i E BE py Neo oor: N 97 W o 15 a 'S 86. E Bast recs ae wives N98 WW sf 165 Ss S74. Booby Sooo. ee. N99 W c 17 S67 BF ME ress a woe Ve N 99 W . le Hoss 8 S755 SE Di i bea ects N 98 W ee '16 « S10 I ER es N 98 W « 16 " S 90) SE Pyne. ose ec ee N 97, W « 15 " G49 ob SSE cee sa N 96 W : As eo S by ee ee wes N95 W ne 13 Ss SW SOuUth: £6. cies cee ante N 94 W & 12 " S42 Ww S by Was eco N 92 W s 10 6" S31 ° We SSW ic ce chee oie eee ee N90 W a 8 6 Gat ow SW Dy eee es o's oe es N 87 W se 5 ee S39 W SW 5 weer eee ernest oe N 83° W Se i? ' 6c S 46 WwW SW: by W.........-- N79 W ce 3 Wily S:53- WwW. WISWe oe vss N75 W oS 7 is S61 W Ww by Sea ee N 70 W & ae) &¢ S67 W PVILESTS eile ieeros aie sy N 66 W £6 16 6c S74 W W by Bere haa s N 63 W as 19 ce S32 W INVEINIVVS rte cae wc bes N 60 W c 22 "ec N90 W NW. by. Wie... Weed IN 59: W 6s 23 ¢< N79 W Wes cape islets igs sisis 00 N 58 W ae 24 'e N60. NW by Nese ce. N59 W oo 23 66 N37 WwW RMI eo cos ea N62 W cae a Ao oe N by W......-+-- .. N 66 W ; & 16 " N27 WwW grees from the compass (where the to see that the same difference exists between the two compasses; or when. the wheelsman is directly on the course given him, a look at the stand- ard compass will show whether things are right or wrong. THE DEV. FOR STANDARD COMPASS. + The deviation is usually ascertained for the standard compass first, and then the steering compass- compared by it afterward. One reason for this is that the standard compass usually shows the least deviation, on account of its elevation, which brings it away from the most of the ship's magne- tism. The- smaller the deviation the more accurately the ship's head cor- rect magnetic can be determined from the ship's head by compass, which, in some cases (when the deviations are large) are two widely different things, strange as it may appear. When the azimuth attachment is used in conjunction with the standard compass it then becomes necessary to ascertain the deviation of this compass first and the steering compass by it. When the pelorus is used 'this- does not make so much~difference. Anoth- er advantage of the pelorus is that if masts, smokestack, etc., interfere with the bearings. on certain courses, in- stead of having to select another range of which the bearing is known, all that. grees W. is necessary is to shift the pelorus to a position of advantage. You could not do this with your standard compass, or any other compass on-eboard, for the simple reason that the deviation would be altogether different than for the position you had moved it from, which you know is due to the ship's magnetism changing its relations with the compass needle, or vice versa. A FEW THINGS TO REMEMBER, Always compare the bearings taken by compass with the known correct magnetic bearing of the same object, or objects, forming the range. Their difference is the Dev. Remember that it makes no dif- ference which is the greater of the two bearings--just subtract the less from the greater and name it accord- ing to the rules given. It should be the simplest matter in the world to name the deviation, if it is handled properly. In fact, all there is to the problem is in the naming of the deviation. This is easy by the rules, but don't just memorize the rules without first understanding their principle. It must be easy to see that on whichever side the correct magnetic bearing is of the compass bearing is the name of the deviation. Take the example off Chicago: The correct magnetic bearing is N 82 degrees W and the compass bearing N 89 de- It is easily seen that the correct magnetic bearing N 8&2 degrees W is to the right side of N 89 degrees W, consequently the Dev. is named Ely. The compass card must be drawn to the right in order to make N 89 de- grees W come where N 82 degrees' W should be. Remember, too, that it does not matter on which point of the compass you start taking the bearings for the Dey. table. .Always take it on the full point when possible. You can always do so by this method. _After. the vessel: has crossed the range on one course; see to: it that there is sufficient sea room to turn and steady on the reverse course. For instance, supposing the vessel crosses on the SSW course, let her come back on the NNW course, and so on. WHEN IT IS MORE THAN 90 DEGREES, The student will have noticed that the compass bearings of this range in some instances are more than 90 de- grees: Ins a .case of this kind. sub- tract the bearing thus found from 180 degrees, and change N to S, or the reverse. Thus, on the compass course East (according to the foregoing ta- ble) the range bore S 85 degrees W, and this from 180 degrees leaves 95