10o 



COMPASS, THE MARINER'S. 



COMPASS, THE MARINER'S. 



106 



time been bestowed in the construction of an instrument than in the 

 attempt to perfect the needle and mariner's compass. Sir William 

 Snow Harris has, in a form of compass which bears his name, adopted 

 the suggestions of Nonnau in 1590, as regards the compensating slides 

 on the bar, and also the opinions of Dr. Knight in 1750, with reference 

 to the form of needle ; but its chief excellence is in the amount of 

 directive force imparted to it. He also adopts the light form of needle, 

 but not to the extent found in a Chinese instrument. 



Enough has been said to show that the precise form and arrangement 

 of the mariner's compass has long been a question of public anxiety ; 

 and still more must its consideration press upon us when to the new 

 armament of ships and the increased use of iron afloat (as already 

 noticed), must be added the increased amount of iron carried as cargo, 

 and the circumstance of increased speed of ships which brings them 

 more suddenly into danger; these beset navigation with difficulties 

 only to be surmounted by a well-founded confidence in the form, and 

 fiii'l'firity in the mode of m'tng a well-made compass, and this can only 

 be attained by careful investigations and unfettered and disinterested 

 conclusions. 



It is worthy of remark here that to such an extent has the public 

 mind at times become embarrassed with this consideration, that in 

 1854 a panic on the Liverpool 'Change nearly excluded for several 

 days the iron ships of the port from freight engagements. It arose 

 from the following circumstance : The late Rev. Dr. Scoresby, with 

 that honesty of purpose and plainness of elucidation for which he was 

 remarkable, informed the merchants of Liverpool of various discoveries 

 as to the causes of local disturbance in iron ships, such discoveries 

 having however a tendency to cast doubt and distrust around that on 

 which hitherto the sailor had relied as his faithful conductor through 

 the pathless oceans of the globe. [ LOCAL ATTRACTION.] The insidious 

 workings of the magnetic influence, then for the first time made known 

 to the commercial world, and this too under the sanction of a meeting 

 of the British Association, naturally alarmed the ship-owner, appalled 

 the merchamVcaptain, and lent its aid towards general confusion. 

 Although the discoveries of Dr. Scoresby are of absorbing interest to 

 the philosopher, and have assisted others in their laboratories, yet 

 to the mariner or the ship-owner these subtle workings of the mag- 

 netic current ought to have presented very little real difficulty, 

 as wag promptly shown in a published address by Mr. Saxby to the 

 ship-owners of Liverpool, and also by the judicious and timely appeals 

 to them by Mr. Grantham, a very eminent marine engineer of that 

 town. The effect of this on the compass question was, the almost 

 immediate production of such a variety of forms of the instrument as 

 were calculated, it was supposed, to pacify the ship-owners ; but it 

 actually left the ship-captain burdened and bewildered with novelties 

 and perplexities which even now, in a great measure, render the cor- 

 rection and use of the compass, notwithstanding its importance, the 

 least satisfactory, the most anxious, and the most tiresome of all his 

 work at sea. This competition, however painful in its early operation, 

 had, in a national point of view, a salutary effect. It loudly evoked 

 the hidden talent of officers in the mercantile marine. It aroused their 

 energies, and demanded of them something beyond attention to the 

 mere routine in which they had been trained. Ship-captains soon 

 found among their numbers many men of sufficient talent to grapple 

 with the compass question, and that large and respectable body, relying 

 on themselves rather than on men of reputed science, began to judge 

 for themselves aa to the merits of the various toys placed into their 

 binnacles by credulous owners ; and many an absurd, though pre- 

 sumptuous and specious form of compass has already been by them 

 consigned to oblivion ; many ingeniously contrived instruments, good 

 in themselves but totally unfit for tailors' Me, have gradually sunk or 

 are yet gliding visibly into disrepute. With that promptitude, however, 

 which characterises Liverpool merchants, soon after the announcement 

 made by Dr. Scoresby, a Compass Committee, seconded by the autho- 

 rities at the Board of Trade, was formed, and a vast collection of facts 

 speedily poured in from those who were interested, and measures were 

 taken to assist navigators, which will be clearly and more properly 

 detailed under the head of LOCAL ATTRACTION in this work. But 

 nothing resulted from their really praiseworthy and indefatigable 

 investigations, calculated to modify the generally existing form of 

 mariner's compaos : nothing new appears to have been suggested by 

 that body indicative of real improvement in the instrument. 



Although we must not in this article enter far into the question of 

 local attraction, yet as its causes have led to some modifications in the 

 form of compasses to facilitate corrections for deviation, &c., it is 

 necessary to notice that the Astronomer Royal, having long turned his 

 powerful mind to the question, announced to the world a theory of 

 local attraction which involves the necessity for soft iron as a part of 

 the compass-correcting arrangement. No greater proof of the diffi- 

 culties which surround the mariner's compass aa a nautical instrument 

 can be adduced than the fact, that, although now some few years have 

 passed since Professor Airy first gave to the world his really simple 

 and elegant theory for correcting by magnets and soft iron, his opinion 

 remains unaeconded and unadopted by the Admiralty, by whom cor- 

 recting magnets are rejected altogether, from extreme and irrepre- 

 hcngiUe, but possibly overstrained, prudence. It is not improbable 

 that a number of the fallacious methods of correction of the compass 

 produced of late, have so deluged the authorities at the Admiralty 



with suggestions thereupon, as to somewhat blunt the intelligence, 

 and thereby obscure the truth, even iclicn offered by the Astronomer- 

 Royal himself. It must also be remembered, and indeed it is a fact 

 well-known to the writer, that many merchant-captains who have 

 had their compasses corrected in port by the use of fixed magnets, 

 have found such error and inconvenience arising therefrom (on account 

 of subsequent changes in the magnetic condition of the ship), that 

 rather than endure the annoying discrepancies and perplexities con- 

 sequent on their use, they have pitched their correcting magnets over- 

 board altogether ; preferring to encounter the magnetic dangers of the 

 voyage with a single well-made compass which they did understand, to 

 tampering with changeable and vacillating agents and appliances 

 which were above their comprehension. Such may account for the 

 authorities at the Admiralty rejecting the use of correcting magnets 

 altogether. 



Taking even Professor Airy's theory of moveable adjusting magnets 

 and soft iron as an instance, how few merchant-captains, unaided by 

 a mechanically convenient correcting apparatus, could follow a learned 

 discussion on so intricate a science as that of magnetism (however 

 valuable in itself) ; much less could they use the mathematical formula; 

 necessary for its application to the mariner's compass. It remains to 

 state that a practised compass-maker, a Mr. John Gray, of Liverpool, 

 an optician of talent well known in all the principal ports of Europe, 

 after study and experiment on an extended scale in which he believed 

 he could corroborate physically the theoretical assumptions of Pro- 

 fessor Airy, contrived a compass arrangement which, apart from all 

 invidious selection, and from a sense of public duty, finds an illus- 

 tration in this article. Several other forms for correction of the 

 compass-needle exist, and each has its advocates, but the following 

 sketches of Gray's compass arrangement give an idea of the form in 

 which the Astronomer-Royal's suggestions are being carried out. 



R 



=(] 



B, Outer* bowl, containing fluid, in which, B 2, inner bowl is floated ; R and 

 K 2, Kims of ouicr and inner bowls ; v s, Springs to keep the bowls In 

 central position with each other ; T s, Tangential screws to adjust the 

 bowls to their centres ; o and o 2, Guides to prevent rotatory motion ; 

 L, Lubber's point; B, Elastic discs; s, Spiral spring; c, Chain boxes for 

 soft iron ; o 3, Gimble. 



The above has, moreover, an interest from being the form 'of apparatus 

 used 011 board Her Majesty's yachts ; and without compromising that 



