THE COMPASS AND ITS REMEDIES. Rock Ferry, 24th May, 1856. Sir,-In your last number you did me the honour of giving to some remarks of mine on the compass question a place in your respected Magazine; I beg, therefore, to be allowed to add a few more, should you deem them worthy. Now as we may confidently rely on the continued vigilance of merchant captains, the material of which a ship is built need scarcely cause public anxiety. But to owners, merchants, and the captains themselves, it becomes a serious question. Considering, as a scientific problem, the change in amount of magnetism in an iron ship, I submit to your readers, and to the Compass Committee, that in my letter of the 22nd ult. the agents in such disturbance are plainly exhibited, perhaps a valuable partial remedy itself is given. In that letter I proved that an enormous amount of magnetic influence is called into exercise from the moment at which the furnaces of a steamer are lighted; that whatever might have been the previous condition of a ship (from direction on which built, from mechanical operations during construction, &c.) there does exist an immense daily production of magnetic power, and this arising from thermo-electric and chemical action, in the disturbance of galvanic distributions from heat, the combustion of coal, the conversion of water into steam, &c.; and this in such quamity, that its not overwhelming the compass altogether, might seem to raise doubts of its presence. I propose, therefore, with your kind permission, to consider the circumstances under which this accumulation is probably dispersed, or 'so disposed of, as to reduce local disturbance even to its present fickle and still perplexing average quantity: for I have proved, and it is admitted, that after a few voyages, or probably after a single voyage, an iron ship attains a more equable condition as regards magnetism; differing little if anything in constitution from a wooden ship. As I am not qualified to write for learned professors, but merely seek to explain to or rather remind shipowners and intelligent and scientific sailors of certain simple principles, as they appear to me to bear on the great question under consideration, I need scarcely apoligize for some slight repetitions in the use of accepted terms; and would here remark that we can as effectually test the quantitative presence of an imponderable fluid like electro magnetism, as of an ordinary liquid. A Leyden jar, for instance, suggests three states of electricity, distinguished as negative, quiescent, and positive; and without our attempting to suggest any precise limit of capacity for electricity, (the source of magnetism,) there is a certain point at which what we may call quiescence, or saturation, is apparent: for any addition of electricity to a boly in that state insures a disposition in that fluid to escape, as by a spark, or by some better conductor than common air. While any diminution of this normal quantity which nature seems in every substance to require to produce this saturation, is shown by the ready transmission of electricity towards it from any contiguous body having its point of saturation more nearly satisfied. I assume, therefore, that the magnetism of an iron ship is purely a question of the positive, or negative, or quiescent electric state of such ship; and that we have been on the wrong scent when merely seeking for correction of compass. Whether we turn the handle of a machine specially arranged to produce electric charges and discharges, (and equally, be it remembered, to produce magnetic currents,) or whether we by lighting furnaces, by burning coal, or converting water into steam, produce the same phenomena in a body not specially arranged for the exhibition of magnetic currents, we have the same elements to work with, with the difference that whereas in the common electric machine we have an instrument, or arrangement, sur rounded totally by atmospheric air, in the iron ship, partly immersed in a much better conductor, and with very considerable superficial metallic contact, and therefore alteration in the electric and magnetic state or condition of such ship as a body will be governed to a certain extent by the proximity of such ship to such conductor feeble or otherwise. Now an iron ship from the stocks the moment she touches the water in her launching, undergoes a change, not from the mere mechanical act of motion alone, as generally supposed, but from the change caused in her electric condition by being placed suddenly (as above observed) in a better conductor than air. She goes into dock, where, in perfectly still water, (but water which has an immense superficial and galvanic action on the metal sheathing of other ships, and which is pervaded in all directions by an intricate network of commingling and untraceable galvanic currents,) into water, I say, peculiarly adapted to influence the electric condition of such ship, whether such disturbance be the work of days, or hours, or seconds, is immaterial; certain it is she undergoes a change, and attains a new state of saturation, for natural electric equilibrium requires this, and is as certain as that a nail placed on a hot plate approaches its temperature. This new state probably lasts until her cargo, perhaps of iron or some metal, is received on board, and modifies still further the state of saturation, any hour changing the amount of this variation from the increasing immersion of the ship in water of a magnetized mass of matter, weighing in some cases thousands of tons! Now it is extraordinary that the Compass Committee announce the change in vessels, wooden vessels laden wholly or partly with iron. To proceed, while such changes are in progress the ship's compasses are examined (carefully, it is true, by competent men, but under great disadvantages) and certain fixed corrections (so called) are recommended for a compass subject to still varying influences! for, next her furnaces are in requisition, and then comes the last great and most enormous change of all, as described by me in your last number. The huge ship, which before was partially magnetized, becomes, as before stated, a receptacle for vast accumulations of active magnetic fluid, and but for certain other laws, which are called into operation, this repletion must destroy the usefulness of the compass altogether. However, it does worse! it affects it insidiously, and at times leads even the cautious mariner to destruction. Better is an open enemy than a false friend! Poor abused compass! Faithful have you been to me and to my father before me, often hast thou led me in safety to my home! I hope to free thy reputation and yet to take thee as my unerring guide! But the subject expands under our field of view! Still other changes have to be described. The bloated and excitably magnetized ship is to be forced through a dense medium, through water holding in solution acids and alkalies, and a proportion of solid matter, which increases its susceptibility to galvanic or electric influences. In passing one body over another, whether it be a stick of sealing-wax upon the coat, or copper sheathing or iron plates over aud through sea water, we, in producing what is called friction, disturb heat, electricity, and therefore magnetism. The paddles revolve, the ship is propelled at a rapid rate, the accumulated magnetism is set in action by the friction of the ship's sides, and partially dissipated; a continuance of the action for some time induces a less sensitive condition of the mass until a state of saturation is attained, which we find in ships of iron which have made repeated voyages. Now having, I respectfully submit, proved that from numerous sources change in the magnetic condition of an iron ship is to be expected, and the Liverpool Committee having demonstrated that it does exist, can it be matter of surprise that corrections recommended on data obtained when a ship is in one state are found useless when the state of that ship has undergone considerable change. In my own anxious and prolonged inquiry into the true state of compass disturbance, it is too apparent that the perfect remedy, if ever attainable, is to be sought rather in the laboratory of the chemist than in the workshop of the compass maker or the studio of the mere experimentalist, or in observations made during a voyage. Experiments on the needle, conducted hitherto by able heads, have led to only partial and mechanical reliefs. Circulars are being issued to all shipmasters by the Liverpool Committee containing forms for the registration and concentration of facts, and it is acknowledged that years must pass before sufficient information from this source can be collected to palliate the grievous evils which afflict British commerce in its shipping. Now, in order to continue my very humble advice that it is to the chemist we must look for aid, I shall ask you shortly to permit me to lay before your readers a few more simple but neglected facts, preparatory to a report which I hope to produce in a future number of the Nautical Magazine having a vital bearing on the real capabilities of the compass itself as an instrument. In treading a path entirely novel, I shall need all the indulgence of the public. However Utopian the idea which has possessed me for some time, I must brave the sneers of those who know only the object in view, not my means of attaining it. Already a warning and friendly voice (but of one in total ignorance of my recent experiments) says to me, "You are pursuing an Ignis Fatuus, a will o' the wisp;" says another, "I have tried everything." Now I remember with extreme acuteness (and it bears so strongly on the present discussion that I scruple not to declare it) on a certain occasion the most illustrious and amiable of our astronomers was holding his delighted auditors as if spell bound in the Senate House of Cambridge by his thrilling description of the approach of a mass towards our earth, which, though unseen by man, was felt by the mathematician to affect parts of the solar system. I remember also his declaration that we absolutely knew nothing of magnetism, and that every fact is precious; and this confession moved me towards a public exposition at Cambridge, before a large audience, some days after, of certain views connected with terrestrial magnetism, and which have never since that day been doubted or disputed. But the exposition was at the time met so fiercely by a learned pro fessor, who, in attacking my groundwork, declared, "that any one having the smallest acquaintance with magnetism must see my error," and he moreover adduced certain 'physical facts in proof of my mistake; which facts I had the felicity of showing were the strongest evidence of the correctness of my views; and although the applause of some hundreds of members of the university attested my success and satisfied my wrath for the time, it left a timidity in proposing publicly even what I feel to be truth. I shall have soon to describe some recent experiments, which, so far as they have gone, engender the hope of my being about to assist the compass question. Even if I fail as to the object sought for, my giving publicity to the experiments themselves will, I have not a doubt, lead to the final shutting off all local attraction on board ship. Why may it not be sought for without the imputation of credulity and intellectual weakness? I can at preesnt only promise to produce sufficient grounds by which to justify and demonstrate the consistency of the hope above expressed. I shall brave the obloquy! In this age say what is impossible? I believe I have found the key, if I cannot unlock the door I shall seek assistance. To the Editor of the Nautical Magazine. I have, &c., S. M. SAXBY. NEW AND CORRECTED CHARTS, &C. Published by the Hydrographic Office, Admiralty, and Sold by J. D. Potter, 31, Poultry, and 11, King Street, Tower Hill. Price s. d. Wolfe, 3 6 each 2 0 Wales, Pembroke Reach, Commander Alldridge, R.N., 1852 - South America, Sketch of River Paraguay from Corrientes to Asuncion, Lieutenant G. F. Day, R.N., 1853 3 0 each 2 6 Falkland Islands, Port Egmont, Keppel Sound, &c., Captain B. J. 1 6 West Coast North America, Port Simpson, Messrs. Inskip, Gordon, and Knox, R.N., 1853 0 6 Polar Sea, Mackenzie River to Behring Strait, various authorities, 1856 8 0 1 6 African Pilot, Part 1, from Cape Spartel to River Cameroons, 1856 2 6 EDWARD DUNSTERVILLE, Commander, R.N. Hydrographic Office, Admiralty, May 22nd, 1856. EDWARDS' PATENT PRESERVED POTATO. Edwards' Preserved Potato having been used in her Majesty's Services many years, proving its value as a vegetable and antiscorbutic diet, we consider it due to those gentlemen to refer to the following favourable testimony from Dr. Rae, of the Hudson Bay Company's Service : "London, 14th April, 1856. "I beg to add my testimony to a host of others in favour of Edwards' preserved potato. I used it on my last Arctic journey and found it extremely useful and beneficial. By mixing it, instead of flour, with our pemican, the latter was made much more palatable and apparently no less nutritious than if flour had been used. "It has the very great advantage of being cooked in a few minutes by the addition of boiling water; whereas other descriptions, as far as I know, of this preserved vegetable require fully an hour's cooking; thus causing a great saving both of water and fuel, two very important considerations either on the Arctic coast or on shipboard. "At York Factory, in Hudson Bay, Edwards' potato is highly approved, and has been a daily dish at the mess table for a number of years past. Since its use there has been less tendency to scurvy. JOHN RAE, M.D., H. B. Co's Service." JOURNAL OF H.M.S. "RATTLESNAKE," COMMANDER HENRY TROLLOPE, ON HER RECENT VOYAGE TO BEHRING STRAIT. At 4h. p.m. on the 23rd February, 1853, we cleared the Needles channel and the wind and sea increased very much. At 5h. 30m. the towing hawsers carried away; we made sail and stood to the westward. At 6h. p.m. Portland high light bore N.W.b. W., about thirteen miles; Needles light, N. 87° E., twenty-three miles. The wind from the northward blew keenly. Sharp snow squalls came on frequently, but they were fair and we stood W. N. and W. S.,-Basilisk in company. As it was full moon, and high water at Portland at 6h. 30m., we did not get the S.W. going or ebb tide until 9h. p.m., but it could not be called against us as the last of the flood sets W.N.W. We kept rather to the southward, to avoid the Shambles, and kept sight of Portland until midnight, when it bore N.E.b.N., thirteen miles. The wind continued steady from the northward; the glass was rising although the weather was gloomy. 24th. At daylight the Start and Praule point were indistinctly seen N.N.E., about six or seven leagues distant. Captain Martin White, in his admirable directions for the English Channel, lays great stress on the rotary movement of the tides, and his elaborate tables appear to prove it; but it appeared that we had been certainly set to the southward since we cleared the Needles. At noon, in lat. 49° 37′ N., long. 4° 13′ W., the wind was North and N.N.W., but in NO. 7.-VOL. XXV. 2 Y |