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TAE MaRINE REVIEW ~~ oe 37 of W by S, which it would were it correct (free from Dev.) This then, to the uninformed man would be the course (W % S) to steer between Eagle harbor and Dev- il's islands, which he bases upon the theory already stated. But not so with the master educated in navigation. He would view it from an altogether different standpoint, and reason it in an entirely different way, because he would possess the proper knowledge upon which the prin- ciple is based. The first thing that he would do. would be to determine the correct amount of the Var. (which he gets from the chart) and apply it to the true bearing of the range to get the correct magnetic bearing. Als the Var. in this case is about %4-pt. Wly., which applied to the true bearing W by S % S gives the correct magnetic bear- ing W by S, as already stated. Now, if the compass is correct (free from Dev.) he knows beforehand that when his boat is on with this range the compass will have to show or point out the correct magnetic bearing of the range (W by S),:and if it does not the difference between what he knows the correct magnetic bearing to be and what the compass says is the Dev. of the compass for that particular point.of the horizon to which the vessel's head was directed. In this case the Dev. will be %4-pt. Wly. and as the Var. is %4-pt. Wly.--the two added together equals 34-pt. Wly. correction, which likewise represents the difference between the true bearing W by S 4% S and the compass bearing W % S. Thus, the skilled navigator analyzes the various portions of each problem that en- gages his attention, separating the different parts compris- ing the "total' compass correction--the Var. from the Dev.--and giving each its proper value, and in each in- stance applying the right kind of remedy. With the above data in his possession the well-informed navigator in shaping the course to be steered from Eagle harbor to Devil's island, will first ascertain' the true course, which in this case is W by S %S; then he as- certains the Var. for the course and position. This he would find to be %-pt. Ely.--the opposite name of the Var. found for the Sault river range. This would make the correct magnetic course W by S % S, and the %4-pt. Wly. Dev. would give a compass course of W by S % S-- a difference of 5£-pt. with the direction or compass course obtained while on with the range, which was W ¥% S. Were this course steered on Lake Huron, where the Var. is practically the same amount and name as in the Sault river, then a good course of it would be made. You will hear captains say that their compasses work good on Lakes Michigan and Huron, but not on Lakes Superior and Erie; meaning that the compass is not "off" as much on one lake as on another. This is because the Var. is jumbled up with the Dev. and vice versa; as the compass works the same on one lake as it does on another, providing that the Var. is accurately allowed for in each and every case. Sometimes the Var. 'is Ely. and sometimes Wly.; likewise the Dev., which is Ely. in one case and Wly. in another. When the Var. and the Dev. are of the same name it makes the compass appear to be more "off? than when the Var. and Dev. are un- like in name, that is, in relation to the true course, for one correction ,counteracts the other. Here is the way this occurs. Supposing on an N by E course the Dev. is %4-pt. Wly. True course from Chicago to Pt. Betsey N by E % E. Var. %4-pt. Ely. Var. and Dev. being equal and opposite in name or direction, counter- acts each other, and leaves the compass course the same as the true course, viz: N by E % E. The captain ts well satisfied with this as his "compass steers a chart course." The compass, nevertheless, has a Dev. of Y-pt. on this course for the correct magnetic course from Chi- cago to Pt. Betsey is N by E % E. To steer N by E 4 true on Lake Huron, where the .Var. is Wily. with this compass, he would have to steer N by E % E; but if it was desired to steer N by. EYE true, as in the case on Lake Michigan the course to be steered by compass would be NNE. In the same example supposing the Dev.'on N by E was /4-pt. Ely. instead of Wly., the compass course from -- Chicago to Pt. Betsey would then be N by E instead of N by E % E. In a case of this kind the captain. would say that "the compass is off 4-pt ;" whereas it is only a quarter point. . a Supposing' that a particular compass had 1, -pt, By Dev. on a SW course, and it was desired to steer a true SW course at the head of Lake Superior where the Var. is 34-pt. Ely. The correct magnetic course in this case would be SW 3 S, and the compass course (4-pt. Ely. Dev.) SW by S % S. In this case the difference between _this and the compass course is 1% points, which the un- wary navigator would call the "deviation of the compass" or the "variation of the compass." The Var. and Dev. in this case, being of the, same name, makes the "total" correction 114 points, but the Var. alone is 34-pt. and the Dev. %4-pt. : Were it desired to steer SW true, by the same com- pass, at the easterly end of Lake Erie, in the vicinity of Buffalo, where the Var. is approximately 1%4-pt. Wly., the compass course would likewise remain the same as the true course, viz.: SW. .In this case the Var.. and, the Dev. are of the same amount, but of opposite names, therefore, one correction: counteracts. the other. Flere, the master ignorant of the rudiments of navigation would say that his compass was true because he was able to steer a true or chart course. Thu', even the novice in navigation, can see why the compass is way "off" in one case and "true" in another; notwithstanding that the deviation remains the same in both cases, Here is another great error that the average master readily falls into. Coming out of a pier or while on with a range, he notes the course by compass, and then looks on the chart or in the lighthouse book, for the bearing. Then the difference between what the compass reads and what the lighthouse book says is what the compass is "off"? The chart and lighthouse book give only the true bearing, the variation having to be applied by the master. Whatever he finds the compass to be "off" for that certain course is the "error,' and whenever he has occasion to steer this course again allows for this differ- ence, no matter what the amount and the name of the variation may be. Should it happen that the Var. for the course is of the same name as for the position found, the course steered will be correct, but if the Var. be different, and it usually is, the course steered will be wrong, and the captain will lay it to every cause, but the right one. The average lake captain imagines that because his compass is adjusted that he ought to be able to steer a true or chart course without so much as even allowing for the magnetic variation existing between the point of. departure and the point of destination. The primary object in adjusting compasses is to reduce large deviations to a minimum, to bring them within manageable limits, thus equalizing the directive forces, preventing sluggish- ness and to cause more readiness of movement of the compass card needle. With a large deviation the direc- tive force on the compass needle is proportionally dimin- ished with the vessel's head on some points, while with a corrected compass the directive force is nearly equalized on all points. ; Perfection in compass adjusting 1s se owing to numerous causes, so that it becomes a ldom attainable, s neces-