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THE Marine REVIEW oa more or less successful.tf But by far the most successful suspension for a dry compass was the Thomson grum- met (Fig. 2). This suspension is an elliptical ring composed of one length militate against the steadiness of the dry' cOmpass;* but) 80 far -"as "fast steamers are concerned, the opinion is that speed, combined with vibra- tion, causes the cap which supports the card? to@ Hitt *shghtly from the '» pivot and fall back again. This would the edge of thé card and touching the _ side of the bowl, is quite enough to _ overcome the earth's directive force on the needles, and stop the card, -- while the ship's head has turned through 10° or more. The earth's magnetic force may then assert itself, Fie 2: THE THOMSON GRUMMET RING. of brass or copper wire twisted sev- eral times round a core wire in such a manner as to give considerable elas- ticity.< "From 1 this {fing gare? Hung athwartships, exactly opposite one-an- other, chains with stirrups in which the trunnions or knife-edged journals of the gimbal ring rest. On the un- der side of the ring sockets are fixed, exactly fore and aft opposite one an- other, which rest on small balls: fixed to the binnacle rim. Figs. 3 and 4 show other systems of spring suspen- sions, but it is a matter of doubt whether those are improvements on the grummet ring suspension. In re- cent years, however, even this ingeni- ous arrangement has failed to meet the increasingly onerous conditions, and apparently the suspension of the card in liquid is the system to which we must look for the best practical results, Whether the failure of the dry com- Pass to cope with the new conditions arises from the fact that the con- Struction of the Thomson card gives it something of a fly wheel action, in turn partly braked by the paper rim, or from the fact that spring suspen- Sions of any kind are not constant, it is certain that when the card is sus- pended in a suitable liquid, which will not change its condition, the suspen- Sion is a constant one. In the liquid compass the card is not actually floated by the liquid, but is sufficiently heavy to poise on the central pivot. It is difficult to ascertain the exact effect of the new conditions which es {The first suspension of compasses by means of gimbals to allow of the compass always taking up a horizontal position, known as Cardan's Suspension," is of such importance at it is in use in all compasses. The sus- Pensions mentioned in this' paper are for another purpose, viz., intercepting the disturb-. ance o tion f the compass card caused by vibra- > etc, quickly set up oscillation on the card, and accentuate any fly wheel action. I have known of 'compasses sus- pended by spring suspensions being actually thrown out of the gimbals. This was possibly due to the move-- ments of the ship and the movements of the spring suspension coinciding. An extraordinary incident came un- der my notice not long ago. In a London steamer, in which the stand- ard compass was placed about 10 ft. from a steam whistle, the card was subject to violent oscillations when this whistle was blown. 'Another compass and card placed in exactly Bic. o: THE KELVIN SUSPENSION, the same position showed no oscilla- tion, and the theory put forward to account for this was that there was some relation between the sound vi- brations of the whistle and the tre- mors of the compass bowl in the former case which did: not exist in the latter. .I am. inclined. to think, however, that: what really +happened was that vibrations were set up in Fic. 4. THE DOBBIE SUSPENSION. the glass of the bowl which caused the pipe, projecting downwards from the center of the glass to prevent the card rising, to strike against the cap, and so set the card in motion. I have not had an opportunity of trying this compass bowl with a different glass, but I imagine the disturbance arose from the glass and not from the bowl. . Captain E. W. Cres C. 2. & No "Rlementary _Compass Man- ual," warns us that. "the mariner's compass is at the best. a delicate in- strument. A fiber that can hardly . be seen by the naked eye, attached to in his and the card go off with a swing." | Considering all the circumstances enumerated, some of us have come to: despair of ever getting a dry com- pass to work satisfactorily under ev- ery condition, and have been driven to experiment, more particularly, with -- the liquid form of compass. mS The objections to the older forms of liquid compass were the interfer- ence with perfect adjustment due to the length of the magnets on the card, necessary to give it sufficient directive force; and the motion set up on the card by the annulus of liquid disturbed by the motions of the bowl, when a ship turned quickly in azimuth. In the new form of com- pass now to be described, these ob- - jections are overcome. Previous to the end of last century, Captain Creak constructed a compass bowl, slightly hollowed out opposite the periphery of the card, leaving a greater distance than usual between the wall of the bowl and the periph- ery of the card, and undoubtedly this was a step in the right direction. In 1901 the writer took out his patent for a form of compass, the main feature of which is that the card is of such small diameter as compared with the bowl, that it is absolutely withdrawn from the annu- lus of liquid disturbed by the motions of the bowl. After being subjected to the most severe tests, this class of compass has been adopted by the British admiralty for service use, and is to be fitted for the standard and steering compasses, in future, in the navy. ° The objections to this compass are the small size of the card, and the - error of parallax, arising from the first Fic, 5. s THE DOBBIE COMPASS,