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- 30 THE Marine REVIEW it: When the decimal is written and it bothers you to read it, do as follows: Write the figure 1 directly under the decimal point, then add a cipher for each separate figure to the right of the decimal point, and you have its denominator; thus, .135-1000, read 135-thousandths. ANSWERS TO CAPTS. HOAG AND SAWYER. Marine Review, Question Department :--I have taken the liberty to write you in regards to two examples taken from ranges in Soo river above the canal locks and would like to know why the var. in these two examples which is westerly, that in the first example the westerly var. is allowed to the right, and in the second example the same amount of var. is allowed to the left in the same quad- rant. The following examples will explain what I am trying i cet at. Wiu1am S. Hoac, Master Str. Sir Henry Bessemer. _ Example No, 1.--Vidal Shoal Channel Range (Soo Canal Ranges) over stern the true bearing of which is WSW 3% W var, 2%4° Wly. = 14-pt. making the correct magnetic bearing of the range W by S. With the range directly over the stern the compass should read W by S if there is no dev. If it should read west of west by south the dev. is Wly., if south of W by S the dev. is Ely., the amount depending on the dif- ference of what the compass shows and W x S. Example No, 2--Pt. au Pins Range true bearing of which is S W % W var. 2%° Wly. = %-pt., which makes the cor- rect magnetic bearings S W ™% W. If your compass reads anything to the West of S W % W the dev. Wly.; if South of S W ¥% it is easterly; if the compass should read S W % W itself there is no dev. and the compass bearing is also the correct magnetic bearing. William S. Hoag, Master Steamer Sir Henry Bessemer :-- You are right; it is my mistake. The correct magnetic bear- ing of the Pt. au Pins range in the Soo river is SW by W instead of SW % W. I allowed the var. the wrong way--to the left of the true course instead of to the right of the true course SW 3% W. On page 261 of Nautical Magazine you will find where I called attention to this and made the proper correction. From true course or true bearing, to correct magnetic course or bearing, allow or apply westerly var. to the right of the true course, and easterly var. to the left of the true course. Ely. and Wly. dev. is applied the same as _ Ely. and Wly. dev. from correct magnetic course or bearing, to compass course or bearing. . Thanking you for your favor and inviting you to come again, Lone. Reply to query of E. L. Sawyer, master steamer Griffin, printed in last week's Review under the heading of "The Subject of Deviation': All that you have said is very. true; you have the correct idea of dev. and understand its changes under the conditions which you have named. You have .merely misconstrued the passage quoted from my article. . - I will quote the whole paragraph from which the passage is taken, and then analyze it: "The uninformed master entertains the idea that because this range and- course are one and the same true directions that whatever the compass reads when his boat is on with the range, represents the course to be steered by that particular compass from Eagle harbor to Devil's . island. These true directions are nevertheless the same, but- it is the change in the name of the var. that accounts for it, the dev. taking no part in the problem, because it remains the same for that heading of the vessel whether in the Soo river or on Lake Superior, providing, however, that the change of latitude is not too great. Where the name and change of the var. is of the same name and amount, this practice is sufficiently accurate for all practical purposes; in fact, it is used a great deal and with good results, but it will not work on the same principle all over the lakes for the reason that the var. is not of the same amount and name." .. This article presupposes that the boat in question is bound up to the head of Lake Superior. She may be light, or loaded, or only half loaded, or otherwise, but whatever trim -- -navigation. she is in at the time of determining the dev. on this range she must retain this same position in the water in order that the same influence on board causing the dev. will remain the same in respect to the compass. The statement that "the dev. taking no part in the prob- lem, because it remains the same for that heading of the ves- sel whether in the Sault river or on Lake Superior," is true under the conditions named. It must now be understood that the amount of the dev. found while the boat was on the Soo range will be identical with the amount with the boat heading correctly on the course between Eagle harbor and Devil's island. Now, the point I endeavored to bring out in the article is simply this: that the geographical direction of the Soo range is identical with the geographical course between Eagle harbor and Devil's island. The unin- formed master will put his boat on this range, note the com- pass course, and then try and make the same compass course between Eagle harbor and Devil's island, as the compass said on Soo range. It cannot be done, simply because the var. ie fot «the «same gi tre two places. © The ~ dev. 15 though; therefore, the dev. takes no part in the problem (when it is combined with the var. as in this case), because it remains the same for this particular heading of the vessel whether in the Sault river or on Lake Superior. It is the change of the var. that is responsible for throwing the vessel off the course. This. then proves the statement made in re- gard to the dev. having nothing to do with it. The statement: "providing, however, that the change of lat- itude is not too great," is of no account in this case. It has reference to the changes of dev. due to changes of the earth's magnetism in sailing over a wide expanse of the earth's surface, such as the change of dip with its influence on verti- cal iron on board. Your letter virtually indorses the sum and substance of the article entitled "What Every Master Should Know." You might well have said that there is no place in the world where scientific piloting is more essential or more re- quired than here on the great lakes. There is no other navi- gation where the course made good is of such prime import- ance; on the ocean, with plenty of sea room, this is not so important, since the ship's position is found from time to time by astronomical observations. I regard the principles of true piloting the most serious problem of navigation. There is much more to the subject than many practical men have an idea. Lake piloting is not sea harbor piloting, nor is it to be compared with it, and, too, it is more difficult and requires more science than sea coast Scientific piloting does not simply mean being acquainted. with the shore lines, land marks, lighthouses, reefs, buoys, etc., etc. These, of course, are the first principles of the science and the foundation upon which based; but true lake piloting is dependent upon a thorough understanding of the catses and effects of var. and dev.; a knowledge of the use of pelorus and azimuths in ascertaining the dev. and its changes; the taking of bearings of prominent points, lighthouses, and other objects depicted, on the chart, and from the plotting the position of the vessel on the chart at regular intervals; also the familiar use in laying courses and correcting same for var., dev., leeway, etc.; a judi- _cious use of the sounding lead in connection with safety curves in getting the required information from the bottom during thick weather, etc., etc. I don't mean by this that one has only to know navigation in order to become a skillful pilot navigator. It requires experience and good judgment together with scientific training. One is of little use without the other, especially in thick weather. One who learns the theory of the science first will acauire its practice much quicker than one who has only the practice and not the theory. A knowledge of navigation gives the master of a vessel