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The magnetic character of an iron ship is represented by five coefficients :

A. Constant deviation.

B. Semicircular deviation.

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Besides these there is another error which in some ships is very considerable, viz., the heeling error.

As the coefficient A is a constant and is generally very small, it is not for the present purpose necessary to enlarge upon it.

B and C are two coefficients representing the semicircular deviation, so called because it is easterly in one semicircle and westerly in the other. It consists of two parts, the induced magnetism, caused by vertical induction in soft iron, which varies. as the tangent of the dip, or as it is sometimes called the magnetic latitude, and the permanent magnetism which varies inversely as the earth's horizontal force at the place.

If the exact proportions of these two parts were accurately known and remained unchanged, the alteration in the semicircular deviation might be calculated for a change of magnetic latitude, but this is not the case.

For convenience, the semicircular deviation is arbitrarily divided into two parts, represented by B and C.

B represents the fore-and-aft magnetic forces of the ship, with its zero deviation when the ship's head is N. and S.; its maximum when the ship's head is E. and W.

It is corrected by the compass adjuster by placing a magnet or magnets in a fore-and-aft line, with their centres in a tranverse line with the centre of the compass.

C, which has its zero E. and W., maximum N. and S., is corrected by placing magnets athwartships, either forward or abaft the compass or both, with their centres in the same fore-and-aft line as the centre of the compass.

D and E are co-efficients, representing the quadrantal deviation, caused by horizontal induction in soft iron, and when properly corrected by soft iron placed on the same level as the compass needle, remain correct for all latitudes.

The heeling error when large, is compensated by a magnet placed vertically under the centre of the compass and is only correct for one latitude.

The object of this paper is to impress on magistrates and assessors that as the semicircular and heeling deviations alter with the position of the ship on the earth's surface, that the deviation table supplied by the compass adjuster is only correct for the place where the ship was swung, and that the responsibility rests with the master to ascertain the change in the deviation of his compass by constant observation of heavenly bodies, both day and night,* when the weather permits.

Further, that if the ship be swung and her compasses corrected by magnets in the northern hemisphere, that it will generally be necessary in high southern latitudes to reverse the poles of the fore-and-aft magnets, correcting coefficient B; that the (vertical) heeling magnet will require constant attention and alteration of position as the ship alters her latitude, and in high southern latitudes it will probably be necessary to reverse its poles.

ENGINEER SURVEYORSHIPS.-We understand that the Board of Trade are about to appoint two Engineer Surveyors of the third class at yearly salaries of £200, rising, by annual increments of £10, to £300, with chances of promotion to the higher classes. The limits of age are 25 and 45, and candidates must have served at sea in charge of engines, and hold Board of Trade 1st class certificates of competency as engineers. Intending candidates should make early application to the Assistant-Secretary, Marine Department, Board of Trade, London, S.W., for the necessary "Forms of Application for Appointment," and for information as to the prescribed examination, &c., &c. Applicants will have to undergo an examination before they are appointed.

[In the introduction to Burdwood's tables will be found a table of bright stars, which, in addition to the moon and planets, are available for azimuths, and in Towson's work "Practical information on the deviation of the compass" will be found the bearing of Polaris for each hour of sidereal time.-ED.]

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CORRESPONDENCE.

REPRESENTATION OF OUR SEAMEN IN PARLIAMENT.

To the Editor of the "Nautical Magazine."

SIR,-Perhaps this is not an inappropriate time to call attention, through your columns, to the large number of men in the Merchant Service who, although they are such an important body in the country, as to make it necessary to legislate specially for them, still have no voice in the election of those legislators. I am speaking of the large number of men who are not householders; their only houses being the house on deck or the forecastle, and who are not on shore sufficiently long to be entitled to votes as lodgers, their stay being on an average about eight weeks in twelve months.

Now although they spend the greater part of their lives on the Great Highway, still their ship is a part of England, and the laws of England govern them the same as they do people on shore; but the ship is more than simply a part of England. She is nothing less than an English village with houses, shops, or rather one shop, and shopkeeper, householders as well; a complete village, if a small one, and everyone living in this village has to pay rent for doing so, not in money but in money's worth (labour). No one supposes that because a seamen has his provision served out to him without his actually handing over hard cash for it that he gets it for nothing-he buys it with labour; and the place he lives in is obtained on exactly the same terms. He pays his rent the same as a man on shore.

His position is just that of a man living in a house belonging to his employer-rent free; but the owner of the house, as a rule, . takes the rent in the shape of work, and so does the shipowner.

Any man on shore who received the same pay as an A.B., and at the same time sufficient money to pay for the provisions usually served out to an A.B., and lodging money in proportion also, would be in a much better position than a large number of mechanics; but because he does not pay rent, or lodging money, he is shut out from having any voice in the government of his country. Educationally he is quite as competent to vote as thousands of the

working classes, and the officers, to whom all the foregoing applies in a much greater degree than to the A.B., are, as a rule, just as able as any class in the country, and they number several hundreds.

It has always seemed a curious thing to me that although the shipowner, according to a great many people, is always trying to murder us for gain, still we are not allowed to look after ourselves a little, but must be treated like infants.

We ought to have a vote. Yes, more than a vote; we ought to have a member to look after our particular interests and then we should have someone who understood our wants, and not be dependent on people whose only experience of sea life is Battersen life, and their only knowledge of a ship the penny boat that takes them there.

I am, Sir, your obedient servant,

A SEAMAN WITHOUT A VOTE.

Southampton, April 7, 1880.

APPARENT AND TRUE DIRECTION OF WIND WHEN SAILING. To the Editor of the "Nautical Magazine."

SIR,-I am very much obliged to you that you admitted my note into your March number.

I see in the April number of your esteemed journal a paper "On the Apparent and True Direction of the Wind when Sailing." Long ago I proposed a small apparatus for finding mechanically, as the author does by reckoning and by a table, the true direction and force of the wind, and I have given it to some of our ships for application.

Take a four-foot rule with flat hinges as shown at A and B. Let A B represent the velocity per hour of the ship, say 12 knots, turn the rule B E in the line of the apparent direction of the wind, and then mark off at C the apparent velocity in knots per hour, say six, then apply the double length rule A D so that it crosses the rule B E at C, A C will then represent approximately the force and the velocity of the wind, and B A C the angle of its true direction with the course of the ship.

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It was especially desirable to reduce in this manner the apparent direction on board of steam vessels.

I should be greatly obliged if any of your subscribers would assist me to procure some reliable observations concerning the winds in the Red Sea and the Indian Ocean which are traversed by some steamers at nearly the same periods in one or the other direction. I have the honour to be, &c.,

Utrecht, 5th April, 1880.

BUYS BALLOT.

GRAIN LADEN SHIPS FROM UNITED STATES' AND CANADIAN

PORTS.

To the Editor of the "Nautical Magazine."

SIR, I beg you will afford me space in your next issue for a few remarks upon the tabular statement of vessels lost from United States' ports compared with those from Montreal, as furnished by Mr. W. J. Patterson, Secretary of Montreal Board of Trade.

He says that from 1873 to 1879 not a single vessel has been lost through cargo shifting. This is satisfactory, and it is only fair to accept his statement as correct, as no doubt it is the result of careful investigation. But the statement marked "F," giving the losses of vessels from United States' ports, seems to me very unfair and misleading, and it is this I wish to correct.

It appears to me that to draw a fair comparison between

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