or Mariner's Steering Compass, is an instrument of great value; that every improvement of it, proposed by men of science or of experience, is intitled to notice. We shall therefore lay before our readers some observations on the defects of the compass in common use, which have fallen into our hands since the article in the Encyclopedia was published. The first is by Captain O'Brien Drury of the royal Navy, and relates entirely to the needle.

"Experience (says this officer) shews us, that the needle of a compass, as well as all other magnets, whether artificial or real, perpetually loses something of its magnetic powers, which often produces a difference exceeding a point; and I am well convinced that the great errors in ship-reckonings proceed more frequently from the incorrectness of the compass than from any other cause.

"Steel cannot be too highly tempered for the needle of a sea-compass, as the more it is hardened the more permanent is the magnetism it receives; but, to preserve the magnetism, and consequently the polarity of the needle, I recommend to have the needle cased with thin, well-polished, soft iron; or else to have it armed at the poles with a bit of soft iron. I have found, from many experiments, that the cased needle preserves its magnetism in a much more perfect degree than the needle not cased; and I have sometimes thought that the magnetic power of the cased needle had increased, while the magnetic power of the uncased and unarmed needle always loses its polarity." This is not an opinion taken up at random, but is the result of what appears to have been a fair and judicious experiment; for our author placed a cased needle, an armed needle, and one without either case or armour, in a room for three months; each having at that time precisely the same direction, and nearly the same degree of force. At the expiration of the three months, he found that the cased needle and the armed needle had not in the least changed their direction; but the other had changed two degrees, and had lost very considerable of its magnetic power. If there was any change in either of the other needles, it was too inconsiderable to be perceived.

These observations seem to be new, and may tend to the improvement of the compass. But it is not with respect to the needle only that this instrument is defective. Mr Bernard Romans of Pensacola well observes, that, on another account, the heaviest brass compasses now in use are by no means to be relied on in a hollow or high sea. This is owing to the box hanging in two brass rings, confining it to only two motions, both vertical and at right angles with each other; by which confinement of the box, upon any succussion, more especially sudden ones, the card is always put into too much agitation, and, before it can well recover itself, another jerk prevents its pointing to the pole; nor is it an extraordinary thing to see the card unshipped by the violence of the ship's pitching.

All these inconveniences are remedied to the full by giving the box a vertical motion at every degree and minute of the circle, and compounding these motions with a horizontal one of the box as well as of the card. By this unconfined disposition of the box, the effects of the jerks on the card are avoided, and it will always very steadily point to the pole. "Experience (says our author) has taught me, that the card not only is not in the smallest degree affected by the hollow sea, but that, in all the violent shocks and whirlings the box can receive, the card lies as still as it in a room unaffected by the least motion.

"Lately a compass was invented and made in Holland, which has all these motions. It is of the size of the common brass compasses; the bottom of the brass box, instead of being like a bowl, must be raised into a hollow cone, like the bottom of a common glass bottle; the vertex of the cone must be raised so high as to leave but one inch between the card and the glass; the box must be of the ordinary depth, and a quantity of lead must be poured in the bottom of the box, round the base of the cone; this secures it on the file whereon it traverses.

"This file is firmly fixed in the centre of a square wooden box, like the common compass, except that it requires a thicker bottom. The file must be of brass, about six inches long, round, and of the thickness of one-third of an inch; its head blunt, like the head of a sewing-thimble, but of a good polish; the file must stand perpendicular. The inner vertex of the cone must also be well polished; the vertical part of the cone ought to be thick enough to allow of a well-polished cavity, sufficient to admit a short file, proceeding from the centre of the card whereon it traverses. The compass I saw was so constructed; but I see no reason why the file might not proceed from the centre of the vertex of the cone, and so be received by the card the common way. The needle must be a magnetic bar, Compass-blunt at each end; the glass and cover are put on in the common way."

A compass of this kind was submitted to our author's examination by the captain of a sloop of war, who assured him, that in a hard gale, which lasted some days, there was no other compass of the smallest service. Mr Romans was satisfied that the officer did not praise the apparatus more than it deserved; and we feel ourselves strongly inclined to be of the same opinion.

It must not be concealed, however, that the ingenious Mr Nicholson seems to think very differently of all such contrivances. In a paper published in the ninth number of his valuable Journal, he labours to prove, that the compass is very little disturbed by tilting the box on one side, but very much by sudden horizontal changes of place; that a scientific provision against the latter is therefore the chief requisite in a well made instrument of this kind; and that no other provision is requisite, or can easily be obtained, than good workmanship according to the common construction, and a proper adjustment of the weight with regard to the centres or axes of suspension. The same author is of opinion, that it would greatly improve the compass to make the needle flat and thin, and to suspend it, not as is most commonly done, with its flat side, but with its edge uppermost; for it being a well-known fact, that soft steel loses its magnetism sooner than hard, it is obvious, that unless both sides of a needle be equally hard (which is almost impossible if they be distant from each other), the magnetic power will, in process of time, deviate towards the harder side.

The Chinese Compass has some advantages over the European compass, from which it differs with respect to the length of the needle, and the manner in which it is suspended. In the compass of China, the magnetic needle is seldom above an inch in length, and is less than a line in thickness. It is pointed with great nicety, and is remarkably sensible, or, in other words, points steadily towards the same portion of the heavens. This steadiness is accomplished by the following contrivance:

"A piece of thin copper is trapped round the centre of the needle. This copper is riveted by its edges to the upper part of a small hemispherical cup, of the same metal, turned downwards. The cup so inverted serves as a socket to receive a steel pivot rising from a cavity made into a round piece of light wood or cork, which thus forms the compass-box. The surfaces of the socket and pivot, intended to meet each other, are perfectly polished, to avoid, as much as possible, all friction. The cup has a proportionably broad margin, which, beside adding to its weight, tends, from its horizontal position, to keep the centre of gravity, in all situations of the compass, nearly in coincidence with the centre of suspension. The cavity, in which the needle is thus suspended, is in form circular, and is little more than sufficient to remove the needle, cup, and pivot. Over this cavity is placed a thin piece of transparent taffeta, which prevents the needle from being affected by any motion of the external air; but permits the apparent motion of the former to be easily observed. The small and short needle of the Chinese has a material advantage over those of the usual size in Europe, with regard to the inclination or dip towards the horizon; which, in the latter, requires that one extremity of the needle should..." should be made so much heavier than the other as will counteract the magnetic attraction. This being different in different parts of the world, the needle can only be accurately true at the place for which it had been constructed. But in short and light needles, suspended after the Chinese manner, the weight below the point of suspension is more than sufficient to overcome the magnetic power of the dip or inclination in all situations of the globe; and therefore such needles will never deviate from their horizontal position."