The mariner's compass does not, however, give the true direction of the various points of the horizon. The needle points to the magnetic North and not to the true North, the difference between them being called the variation of the compass, which differs widely in various parts of the world, being sometimes easterly and sometimes westerly, and constantly changing. The amount is generally marked on the charts. In New York the variation for 1894 was 8° 26´ West, or three-quarters of a point to the West of the true North. Thus, to make good a true North course, the vessel would have to steer North three-quarters West. A rule easy to remember is that westerly variation is allowed to the left of the compass course, or bearing, and that easterly variation is allowed to the right of the compass course or bearing.

To convert true courses and bearings into compass courses and bearings with variation westerly, allow it to the right of the true course or bearing, and with variation easterly allow it to the left of the true course or bearing.

Deviation is another error of the compass caused by local attraction, such as the ironwork and iron ballast in a boat, or the proximity of a marlinespike to the binnacle. In a wooden boat, if proper care is taken, there should be no appreciable deviation of the compass. Deviation can be discovered by swinging the boat as she lies at her moorings, having first obtained the true magnetic bearing of some distant object, such as a lighthouse or a church steeple. As the vessel's head comes to each point of the compass, a compass bearing is taken of the object, and the difference between that bearing and the true magnetic bearing is observed and noted, and afterward tabulated. It will often be found that the deviation differs not only in amount, but in name, for different directions of the ship's head, being easterly at certain points and westerly at others.

The rule is to allow westerly deviation to the left to get the correct magnetic course, and easterly deviation to the right to get the correct magnetic course.

To find out the error of the compass in order to steer a true course, the sum of the deviation and the variation when both are of the same name, and their difference when they have different names, must be ascertained. For instance, deviation 20° West and variation 25° West, would give an error of compass 45° West, which should be applied to the left.

If the deviation was 20° East and the variation 10° West, the difference between them would be 10° East, which compass error should be applied to the right to steer a true course.

In order to find the compass course or course to steer, proceed as follows, the true course being North 40° East, the variation being 38° West and the deviation 18° East:

Another example is given where the variation and deviation are both easterly and the true course is S., 75° West.

A volume might be written on the mariner's compass. It is a fascinating study, but unfortunately my space is limited.

There is another correction to the compass that the amateur should have cognizance of. It is called leeway, and is, in untechnical language, the drift that the ship makes sideways through the water because of the force of the wind or the impulsive heave of the sea. Some craft, because of deficiency in the element of lateral resistance, such as in the case of a shallow, "skimming-dish" sort of a boat, with the centerboard hoisted up, will go to leeward like a crab. Others of a different type, such as the "plank-on-edge" variety, with a lead line attached, will hang on to windward in a wonderful manner. It requires, therefore, a certain amount of judgment as well as of knowledge in this particular section of nautical lore to be able to estimate with any degree of approximate certainty the leeway a vessel may happen to make. It should not be forgotten that build has much to do with this, and that trim and draught of water are also two powerful elements in this connection. For instance, a boat with outside lead and a centerboard in a strong breeze and a lumpy sea, so long as the wind permitted her to carry a commanding spread of sail, might make no appreciable leeway, but, on the contrary, might "eat up" into the wind. But given the same boat without the lead and without the adventitious aid that the centerboard affords, she would be compelled to dowse her muslin at the first puff, and as a purely physical consequence she would retain no hold on the water and would drift off to leeward like an irresponsible she-crab.

Thus leeway must be estimated by experience. It is often a most disturbing quantity, especially when the weather is foggy and the channel in which you are steering is perplexing on account of rocks or shoals. I have already expatiated on the wisdom of anchoring in such a contingency as this whenever the elements will permit. But, of course, one is a slave of the winds and the waves, and "bringing-up" is not always possible. I should, therefore, advise the amateur to carefully watch his boat and endeavor to find out approximately the amount of leeway she makes when the first reef is taken in by comparing the direction of the fore and aft line of the boat with that of her wake. This method may also be pursued with advantage under all conditions of wind and weather, and by this means a moderately correct and very useful table may be made.

The old navigators like the Drakes and the Frobishers had this matter arranged for them, so when they sailed forth on voyages of great emprise and portent they were guided by certain tabulated formula that gave them full and implicit directions for the allowance of leeway. Thus the skipper of a ship with topgallantsails furled was told to allow one point; when under double-reefed topsails, one point and a half; when under close-reefed topsails, two points; when the topsails are furled, three points and a half; when the fore-course is furled, four points; when under the mainsail only, five points; when under the balanced mizzen or mizzen staysail, six points; and when under bare poles, seven points.

This antiquated method of computation answered very well, for those sterling and sturdy navigators of the olden times seemed to have had a rare faculty of achieving their adventurous purpose and of gaining, too, both fame and fortune. But the commander of a clipper ship, with whom I sailed as a youngster, undertook to demonstrate to me the absurdity of any such hard-and-fast rule. We had carried away our three topgallant masts, off Cape Agulhas, while threshing hard against a westerly gale. They were whipped out of us like pipe-stems. It took all hands a whole day to clear away the wreck. Next day the weather moderated sufficiently for us to have carried every stitch of canvas could we have set it. There were a number of vessels beating round the Cape, and all took advantage of the cessation of the gale to spread all their flying kites to the breeze. Our ship, under three topsails, inner and outer jibs, foresail, mainsail, crossjack, spanker, foretopmast, maintopmast and mizzentopmast staysails, beat all the fleet. When it came on to blow again we were the first to reef, because some of our rigging had got badly strained in the squall that took our topgallantmasts away. Still we maintained our lead, although jogging along comfortably while our opponents were driving at it, hugging their topgallantsails and with lee rails under.

"Now," said our captain, coming on the poop after he had worked up his dead reckoning at noontime, "you see all those ships dead to leeward—well they ought to be to windward of us unless all the books on navigation are wrong. I have entered in my traverse-table the courses we were supposed to have made good under the old rule, and have thus proved its falsity. The fact is the ships that were turned out in the days when these nautical axioms were first propounded were built by the mile and cut off in lengths to suit. They had no shape to speak of below the water-line, and perhaps the rule applied to each alike. Times are different now, and leeway must be determined by the model of the ship."

The rule for reckoning leeway is as follows:

Wind on starboard side, allow leeway to the left.

Wind on port side, allow leeway to the right.

Or you may thus define it:

Vessel on starboard tack, allow leeway to the left.

Vessel on port tack, allow leeway to the right.

In this connection it might be well to urge the young mariner against keeping his boat all a-shiver and bucking against a head sea, and all the while sagging off bodily to leeward. It is better far to keep the wake right astern and keep way on the vessel—unless, of course, the weather is too violent.

The direction and rate of tides and currents have also to be allowed for when correcting a compass course. Thus in crossing Long Island Sound from Larchmont to Oyster Bay in thick weather, the magnetic course as given in the Government chart would have to be rectified and allowance made for the condition of the tide, whether ebb or flood, or your boat might never reach her destination.