SEVERAL years ago I was perusing an excellent article in the Nautical Magazine, on the Mariner's Compass, by Mr. Walker. He describes and illustrates in a very clear and satisfactory manner all the inconveniences of making the southern half of the compass card heavier than the northern, and proposes his ingenious contrivance for retaining the card and needle horizontal, without adding any weight to the southern pole. The question occurred to me, why should we require the needle to be horizontal, when we all know that it has a great tendency to dip? Have we any reason, I may say any right, to force the needle to assume an unnatural position? Why should we persevere in forcing it through an arc from its natural inclination of 62° 12′ in the Black Sea, and no less than 69° in England, thereby voluntarily introducing all the consequent evils, as if purposely to display our ingenuity in overcoming them.

I could scarcely find any argument in support of this obviously inconvenient custom, and considering it the first cause of that inefficiency against which we desire to find a remedy, I began to look for a mechanical contrivance by which a single (and edgebar) needle could be kept as near as possible in its natural position in every latitude, without interfering with the necessarily horizontal position of the compass-card; keepNO. 12.-VOL. XX.

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ing in mind that the compass is not required to be such a delicate instrument as that known as the dipping needle.

After various more or less successful, and more or less complicated, devices for arriving at the solution of this problem, I found out one which I will now describe, and which has been tested and compared with the ordinary compass, during protracted cruizes in the Black Sea in small craft, in boisterous weather, and under the influence of the comparatively short seas, peculiar to all Mediterranean waters. Experience has proved, that it is incomparably easier for the helmsman to steer by this inclined needle compass, than by that with a horizontal needle; and that whilst, during heavy rolling motions of the vessel, especially when steering courses near the magnetic meridian, the oscillations of the latter would be, for instance, one point on each side of the lubberline, those of the compass with the inclined needle, would be half a point only, or as much as the vessel herself may be supposed to have in reality yawed on either side of her proper course. The explanation of the reason why the inclined position of the needle at first sight apparently inconvenient, (because centuries have accustomed us to see it horizontal,) should make the compass steadier, consists in the simple fact of the equal distribution of weights on both sides of the E. and W. line of the card; there being no other, except those by which the card is balanced horizontal previous to the needle being attached to it. In addition to this fact, it may safely be concluded, that the magnetic force, being allowed to act in the direction most agreeable to its full development, and at the same time being arranged in such a manner as to have no motion independent from the card, has more power for steadying the whole apparatus, and for retaining its intensity during any length of time. In fact, the card and the needle, each of them separately, and both jointly, tend in this instance to produce the effect of stability, and to counteract the disturbing influences; the one having been balanced to remain horizontal, and the other clinging with all its might to its natural inclined position.

It is but fair to add, that after having tried my compass several years, I found that the idea of the utility which would arise from allowing the magnetic dip to be introduced in the construction of compasses, has occurred to several persons in England, at the same time or before me. But together with this discovery, I have found, and state it without the least intention to undervalue their merits, that none of the various schemes for restoring to the magnetic force of the compass needle its natural position, have been found to answer practically; and that, besides, in those compasses where the needle or needles have been adjusted in such a manner as to remain free to dip in high latitudes if they can, (or as much as they possibly can,) on account of their mode of suspension they were invariably balanced in such a manner, as to remain horizontal or nearly so in England. Besides a striking proof of their not being intended to dip, is in the fact that all the bowls for those compasses have been made scarcely deeper than those for the horizontal needles. The reason for such inconsistency, lies in the various compass-makers' opinions, that, "it is more ship-shape and suug," as if

there was not room enough on board any size of ships for a deeper bowl, provided it was useful! and that after being magnetized, the horizontal compass needle "would incline the card only some 15° or 20°," which inclination of course it does not exceed, being unable, simply from the mode of suspension, to assume the angle of 66°, shown by the dipping needle.

The best among those contrivances as far as I know, is Pope's single needle and another double needle compass. In both, the needles are left free to oscillate in the vertical plane, and in both, the axles of rotation, on the centres on which they are suspended, are above the centre of gravity of the needle, as may be easily seen by the sketches A and B. The same sketches will show, that if the centre of gravity be on the same vertical line with the point of suspension of the card when the needle is horizontal, it will recede from this line with the least inclination of the needle, and thereby powerfully oppose itself to the tendency of the needle to dip. Fig. D, represents the principle advocated in this paper, and is annexed for comparison with Pope's mode of suspen

sion.

After this brief digression and without further discussion of other people's schemes, I will at once proceed to the description of my own, the obvious contradictions in which account for it not being used.

A central portion of the card, (Fig. 1,) equal in diameter to the outer diameter of the central portion of the needle, is cut out of it.*

A light brass plate, a a, consisting of a circle in which the cap is screwed and of two rectilinear arms, is screwed to the card, through these arms, over the central aperture, in the direction of the meridional line. The circle of this plate has on its upper, as well as on its lower side, in the direction of the east and west, small semi-cylindrical grooves bb, for the reception of the axles d d, of rotation of the needle.

The ends of the needle e e, are edgebar, and the central portion is flat; the inner diameter of the latter being nearly equal to the outer diameter of the circle of the brass plate. Brass axles d d, are screwed in the sides of the central portion of the needle, transversely to its length; and so as to project about one-eighth of an inch inside of the central portion.

When these axles are placed in the upper grooves of the brass plate, and the cap is screwed in its place, the latter presses the axles in the grooves, and by this precludes all independent movement of the needle.

When the needle is thus affixed to the brass plate, its lower end (the northern in north latitude,) is inserted through the aperture of the card, and the brass plate screwed to the latter.

When the plate, with the needle and the cap, is screwed to the card, the needle must be moved to an inclined position, making the lower end approach the north point of the card. After this, the card is put on the pivot, and if its north part proves to be lower than the horizontal line, drawn round the inside of the bowl, it will be a proof that the

It has been found useful in practice to make the east and west portions of the card heavier by screwing under it, in this direction a long brass plate O W, with a circular opening in the middle to correspond with the aperture of the card, and with two slides to balance the card horizontal.

needle is too horizontal; if higher, too vertical, so that the proper inclination to which the needle must be adjusted, is made apparent by the horizontality of the card*, and the lower the cap is made, the more sensitive will the card be to the difference of dip, as the vessel changes her latitude.

The diagrams E and F will easily explain these self correcting principles of this inclined needle compass. Suppose the line N S (fig E) to represent the true magnetic dip of the latitude in which the vessel is, and is the horizon, which in the bowl is represented by a line drawn round the inside of it in the plane of the card. When the needle is adjusted so as to form with the card an angle equal to Ses it will coincide with the dip and the card will be horizontal. Suppose, on the other hand, that the needle be adjusted so as to form with the card an angle S'cs, greater than the dip, the natural tendency of the needle being to coincide with the dip, the point S' would in the present instance strive to approach the point S, and the needle not being free to move without the card, would elevate the northern part of the card to the point n'.

If, on the contrary the needle forms a too small angle with the card, say S" es (fig. F,) the same law tending to approach the point S" to S would depress the northern part of the card to the point n". Thus, the apparatus will show itself whether the angle the needle forms with the card be correct to the dip, and if not so, how much it must be increased or diminished.

On the vessel's approach to the polar regions, the needle will require to be nearly vertical. Then, on account of the pivot interfering with such a position, it will be necessary to add to the opposite pole of the card, a portion of that differential weight, by which the horizontal needles are encumbered in ordinary latitudes.

On the contrary, by approaching to the magnetic equator, the needle will require a more and more horizontal position, and, at last, a parallellism to the card. Although the needle may be brought very near to the latter position, it cannot attain it entirely, (without making the mode of suspension more complicated, as will be seen hereafter) unless taken out and screwed on the lower side of the card, to the same brass plate a a through the holes ff, provided in the needle for that purpose. There is, however, a simpler mode of using this compass when crossing the torrid zone. In a steam boat, for instance, when passing those regions in a short space of time, instead of unscrewing the brass plate for taking out the needle, the card may be for the period balanced horizontal, and when the line is crossed, the card, (which for that pur

I have had formerly a vertical semi-circle affixed over the cap to the upper side of the brass plate, inside of the central ring of the needle, which semi-circle could show in degrees the angle to which the needle was adjusted; but dispensed with it entirely for the sake of simplifying the whole apparatus, and because a compass needle cannot, and is not required, to show the exact dip of the latitude of the vessel. Indeed it is quite enough for all practical purposes, that the needle should be within ten or fifteen, and perhaps even twenty degrees from the line of dip.