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side screw. To revolve or set the dial, unclamp both screws. A brass washer with a rimmed edge separates the dial from the attachment so that one does not interfere with the working of the other. The whole thing is so simple that any- one looking at it can understand the ar- rangement in a few minutes. THE INVENTOR OF THE PELORUS. The pelorus is the invention of Lieut. Friend, an English naval officer, and while simple in principle and construc- tion, its utility is so great that every ship should be provided with one. With this useful instrument ship masters can easily and quickly determine the devia- tion of their compasses. It can be used any place on board where an unobstruct- ed view is to be had. The attachment fitted on top of the standard compass, such as the alidade, and other instru- ments, cannot be employed as can the pelorus; for so soon as the. ship's, bin- nacle containing the compass, or any compass on board, was shifted from one position to another, the magnetism of the ship would bear different relations to the magnetic needles of the compass. Not so with the pelorus, which is non-magnet- ic. The pelorus is purely a bearing instru- ment, and its advantage and convenience lie in the fact that it can be employed in getting the bearing of.an object from any certain compass whose view is ob- structed by masts, smokestacks, etc. It AN AZIMUTH ATTACHMENT, is, of course, used in conjunction with a real compass. .It is a dummy and really takes the place of the steering or navi- gating compass during the time that the bearing-is being taken. WHY IT IS A DUMB COMPASS. The pelorus is really a substitute for any compass on board from which a 'bearing is to be had or taken of a land object or of some body in the sky; for it must be plainly seen that if the com- pass dial of the pelorus is set to the UAE MARINE REVIEW same heading as that of the steering compass (if this is the one you wish to take the bearing from--it makes no dif- ference which one you use so long as you set the pelorus to the same reading or heading), the bearing by pelorus must be precisely the same as though it were taken by the steering compass. We fur- ther know that it would simply be im- possible to get a bearing by the steering compass even though that instrument be supplied with an azimuth attachment or bearing indicator, on account of being hemmed in by the sides of the pilothouse. Hence, the truthfulness of the statement that the pelorus can be employed where the compass cannot, and in this lies its chief merit. NOT NECESSARY TO OCCUPY PLACE OF COM- PASS. It must be understood that it is not necessary 'to set the pelorus up, or to have it occupy the same position of the com- pass you are using it for. The pelorus can be set up in any part of the ship, so long as its fore-and-aft marks are set either in the line of the keel, or parallel therewith. The principle of the pelorus is merely. this, it measures the horizontal angle between the object and the ship's head, THE DEV. OF ANY NUMBER OF COMPASSES. It is also possible by means of the pe- lorus to steady the ship's head to any desired course and to determine the devi- ation of any number of compasses on board at the same time and as easily as ' in getting it for one compass. No other instrument can perform this feat. In taking land bearings (at short range) the pelorus must be set up some- where near the compass that the pelorus is taking the place of. This is for the purpose of reducing the angle from the object to the position of the compass and that of the pelorus. In case the shore object is close aboard, the bearing by pelorus, if far removed from the compass it is set to, may make a sensible dif- ference in the two lines, if taken from one or the other, that is, if the bearing were observed from the compass station, or from the pelorus station. Where the object is at a considerable distance from the ship (5 or 6 miles) the difference in the angle should be of no account. The pelorus can be placed anywhere on the bridge without trouble from this cause, with the sun or a star, this would make no difference whatever. A CARD WITHOUT NEEDLES. The card of the pelorus is what is termed "dumb card'--that is to say, a compass without needles--made of brass, entirely unmagnetic, and not partaking in any way of the compass, except that its face shows the points and degrees in the usual manner. The card is something less than 7 in. in diameter. It would be an improvement to have the card 9 in. 29 in diameter, to get larger marginal di- visions, so that bearings of the sun could be determined more minutely than with a smaller card. Where the vertical mark (lubber's mark) on the bar carrying the sight vanes meets the edge of the card, read off the bearing, the card is either clamped, to the ship's course, or the FIELD'S PELORUS, 4 course that the ship is desired to steer. How to use the pelorus with the sun is fully explained under azimuths. IMPROVED PELORUS AND AZIMUTH. | An improved pelorus and azimuth at- tachment is that made by Negus. In this instrument the compass face or dial (showing the points and degrees) is made of a glassy composition, like that of a watch dial, instead of a paper dial, which a good many of the older kind contain... Rain or snow has no effect on it, and eas- ily admits of coal and grain dust, and the like, to be cleaned off its face without the least trouble. This face is a great convenience, for it becomes absolutely necessary to use this instrument in every kind of weather. The degrees and points on the card are clear and well-defined, and will always remain so. The instru- ment must, of course, be handled with a certain degree of care, to prevént the glass dial from breaking. ee HOW THE SUN'S SHADOW IS MADE, | The improved azimuth attachment has, : instead of the sliding eye-piece, a prism- glass, hinged so' that it can be set to any angle, and the sun's bearing is made by reflection. The prism focuses the sun's reflection to a bright perpendicular shad- ow like a pencil line. is about an inch high, and about the width of an ordinary lubber's mark. On the reverse upright of the attachment from the one carrying the prism, and near its base is.a perpendicular slit fitted. with another mirror, and when the re- This shadow line