ward of these islands; and thus his eleven passages from the Lizard to the line would have been lessened from an average of 36.9 days to about 31-2 days, which, is nearly the average of my passages by this route during the last sixteen years. The writer is extremely desirous, for obvious reasons, that a lighthouse should be placed on the Rocas. I beg to observe that there is a reef of rocks a short distance to the eastward of the Cape Verd Islande, on which more than one ship that has sailed by the eastern route has been wrecked, and as this extreme eastern route is becoming more frequented as it becomes better known, I think there is quite as much reason to place a light on the reef referred to, for the benefit of those commanders who might be foolish enough to sail too near it, as there would be to place a light on the Rocas; which could not possibly be of any practical benefit to any ship proceeding to the southward, unless it was bound to Pernambuco, or the parts in its vicinity. Permit me to state in conclusion, that my statements are not mere opinions." I have tried the three different routes, and at different seasons of the year, and I conscientiously believe that in any month of the year no ship can pursue the track recommended by Maury with advantage, except in very rare instances, and that in the months of June, July and August, his route is frequently attended with detention and sometimes with disaster, and I have no doubt whatever to these directions is mainly attributable the great loss which has so frequently taken place on the Rocas! The writer of the letter is quite right when he says "Truth will prevail," but if I may judge from conversations which I have had on the subject with a great number of commanders, whose experience and respectability are quite equal to his own, I am disposed to believe that it will prevail in a manner that will greatly disappoint his expectations. T. HEDGER. THE MARINER'S COMPASS AGAIN! In these days of steam and iron along with great circle sailing (whereby the shortest distance between two places is at once seen) it is no doubt easy enough, by means of tables in use to find at all times the course to steer. But valuable as such tables undoubtedly are and essential to the finished navigator, there has arisen of late years, by the extensive employment of iron in ships, an enemy to the accuracy with which such tables would enable a vessel to keep always on the line of the Great Circle. And this enemy has taken his concealed position in the very heart of the seaman's old and tried friend the compass. When seamen in former times had nothing but the variation of his compass to consider, this was easily allowed for, easily found, and they were satisfied, (to say nothing of a small amount of NO. 2.-VOL. XXXV. N local attraction, as it was formerly styled) they were satisfied to set down to the score of current any little difference that might be found from day to day between the position of the ship at noon by reckoning and that by observation. That difference was generally small and might be accounted for in steerage, drift, or as we have said current. But ever changing time has introduced a fresh evil-unfortunately too a necessary evil, for evils may be looked on as of two kinds, viz., necessary and unnecessary. Our ships have become so essentially iron in their hulls and fittings, that the compass is no longer the tame domesticated creature it used to be. It has assumed a very formidable ship's variation, besides its old legitimate and intelligible one, to which all seamen were accustomed and could find and allow for readily enough. And this new ships variation, the effect of the iron composing the ship and her fittings, is ever found to be of a chameleon kind, always changing as the direction of the ship's head, is altered; and besides that it is fitful and fanciful, not only changing with the direction of the ship's head but also differing in different hemispheres. And even more than this, even the amount of its varying with the age of the ship that is, it will decrease in its amount or intensity as the ship advances in years. So serious an obstacle to correct navigation is at once not only a serious evil, but is actually a necessary one. The shipowner says he must have an iron ship and would be inexorable because an iron ship is economical. Nothing would move him to abandon iron as being the insidious enemy of the compass. Again, as to ships of the state! who, in the course of his plans and devices within a government office ever troubles his head about the compass? Iron tillers, staunchions, funnels, and boats davits were bad enough as they gradually came. They all had their own tricks on the poor compass. But who cared for that, certainly not those who planned those neccessary articles of a ships furniture, although they might have a vague suspicion after all that the compass was quite as necessary for navigation as their wares were for the use of ships. However, these were mere toys, mere playthings to what we have now to contend with. Iron has indeed become not only the material for the construction of the ship, but being always those means of offence and defence employed by the ship of war, has become so tremendously exaggerated that employment of iron has surpassed all reasonable bounds, considering that after all her navigation must depend on her compass ! It would not be easy to increase iron beyond its present amount in our ships of war. And, whatever may be the effect of all this on the compass, it is looked at with the same expectation as in former days when there was nothing of the kind, that it is equally expected to do its duty. Well, be it so, it is an invaluable servant, one without which a ship cannot go to sea. Still it is surrounded by difficulties, assailed by forces that have no regard for the magnetic pole of our globe to which the compass owes its allegiance; in fact, the poor compass is fairly bewildered, and not all the doctoring it has had performs a radical cure; it is "sick at heart," and must be relieved if we are still to navigate the ocean. Matters have arrived at their worst, the crisis has come, and something effectual still must be done to save the compass for the mariner's use. But Columbus himself had the same difficulty in some degree, to contend with. It is to him we owe the discovery of the variation of the compass, and like him, we must refer for assistance to the heavenly bodies. He knew by the height of the pole star that he was in the latitude of his convent of La Rabida, when he was in the West Indies, and shaped his course accordingly across the Atlantic, and we must appeal to the sun to tell us the erior of our compass, as he did, in the midst of far greater troubles by which it is assailed than he had to deal with. The heavenly bodies in fact, when we are out of sight of land, are our very last resort, and happily, when heavenly things are resorted to for assistance by mankind in his need, they never do deceive him! So wrote Young: "Invisibilia non deceipiunt!" This leads us to the consideration of two ways of using the heavenly bodies for the correction of the compass-one is by means of the spherograph, and the other consists of the computed tables of the sun's trne azimuth lying before ns. The readers of the Nautical will at least give us credit for being alive to the compass difficulty long ago. They will remember Mr. Saxby the inventor of the spherograph proclaiming it, and especially his long paper in our last volume, wherein he showed it had been used with success. And they will also perhaps, remember our notice in vol. for 1864, p. 557, of tables of the sun's azimuth by Staff Commander Burdwood, the continuation of which has just been published. Now we are not deciding which should be preferred of these two methods of finding the sun's azimuth. Such does not belong to us. And the navigator knows as well as we do which is easier to do, to use such tables with time at the ship, and to take out the azimuth from them, or to obtain the azimuth by Mr. Saxby's spherograph. We say that the choice of either method or the adoption of both is left by us entirely to him. But it is not difficult to foresee that one of them will become the favourite hereafter and it will undoubtedly be that which will give the best result after employing the easiest means of arriving at it—a custom which generally settles all such matters. Whichever that may be, it is now our business to record an extension of the tables of Staff Commander Burdwood of the navy, in their progress towards embracing the whole range of the globe from the equator to the parallel of 56°N. & S. In our volume for 1864, p. 557, we noticed the appearance of the first instalment of these valuable tables. We may now announce the appearance of those for three more degrees of latitude to be added to them, thus completing the range from 56° to 43° N. or S. This collection includes a large navigable tract of the globe, but only a small portion of what is yet to be done. And even in our own immediate parts it only includes the navigation to the St. Lawrence and the shores of Nova Scotia. But when it is considered that it extends to the same range of South latitude it cannot be denied that a large and very important space of navigation is completed. With this in the possession of the captain of any ship he has got what we might call the "whip hand" of his compass. It may take any fancies it pleases, may point in any direction to which iron may attract it, but at any time when the sun is up and its bearing may be had, the truth or error of that bearing is at once determined by these tables, and the whole error, including variation and deviation may be allowed for accordingly-all in fact that the seaman wants to know. Now in the case when the sun is not visible, as so often occurs, the seaman must do as best he can. He might get the pole star or others at night, or he may have gone over the same ground; or he may be able to infer, from some previous observations, what actual compass correction he has to allow-but with these tables as far as they go and as far as weather allows, the compass need no longer deceive him. not. It is assumed by their author that the time at the ship is always known, and she must indeed be a badly regulated craft where it is The chronometer should always give it with the reckoning approximately until the morning sights are taken for time, as usual in every ship now. By Lynn's tables, which are very well known, the sun's altitude was required to be taken for the observation as well as the bearing. The advantage of these before us will be seen at once to consist in doing away with the necessity of always observing the sun's altitude when his true bearing is required, when also the time can be more easily commanded. For instance, a glimpse of the sun may give the compass bearing and the time known when his altitude could not be measured on account of the clouds or rain obscuring it. The facility of thus getting the compass error is so great that it is fair to illustrate it by the example given. Here is the example : : March 2nd, 1864, in lat. 49° N., long. 10° W. (head East) ship time 8h. 12m. a.m., sun's bearing by compass was S. 44° N. 185°E., what was its error. Now by the tables The sun's true bearing was Variation obtained is then And the deviation or error E., or N. 120° 22′ E. 15 8 W. 25 0 W. 9 52 E. So that the ships time being always known merely a bearing of the sun is all that is necessary with the latitude. We may also add that the time in the tables is taken at every four minutes to which the azimuths under their respective latitudes are calculated for the sun's centre. We shall therefore look anxiously for the completion of these tables, and consider in these days of iron and sadly erroneous compasses that they are actually essential to the safe navigation of every ship on the ocean. While on this subject, we have received a letter respecting the compass in iron ships, that will not be out of place here. It runs thus: Trieste, Dec. 22nd, 1865. "Sir,-In your paper of the 9th inst. I read an account of the stranding of the Hector steamer upon the Codling Bank, and that the Court came to the conclusion-The accident must, therefore, have risen either from a fault in the compasses, or what was stated by the witnesses was false,' &c. "Now, Sir, permit me to inform you that the steamship under my command has the same sort of error in her compasses which caused the stranding of the Hector. I am obliged to steer down Channel S.S.W. by compass, which course takes me from ten to twelve miles outside the Tuskar; and this voyage, coming down Channel in the gales of the 21st to the 23rd of November, I got over on the Irish shore, although I was steering S.W.b S.S. (I allowed the half point for the heavy N.W. gale). These steamers carry large quantities of iron as cargo. I believe it has a great tendency to affect the compasses, for during my experience of ten years, in seven iron steamships, I never found one of their compasses to agree with the deviation cards. After proceeding to sea, I have seen some most erroneous, with the corrections noted the wrong way; therefore I never trust to deviation cards; but, on my passage from Liverpool, I always bring the Skerries Light and South Stack Light in one, and put the ship's head in that bearing, which gives me the error for the S.W.W. course down Channel. "I have been Chief Officer with many Commanders in steamers. I have never seen any of them try their compasses by the above-mentioned lights. It would greatly relieve the anxiety if masters, on their first voyage in iron ships going down St. George's Channel, proved their compasses for the Channel course by this method. I have an opinion that iron ships, as they get older, lose their magnetic influence on compasses, and that they would be as well navigated without all the magnetic bars that are placed round the compasses corrected in dock. We steer this ship amidships. I have tried the experiment on the after compass by taking the magnetic bars (or compensating bars) away. I find it is much more correct. "It is a pleasure to read that the Captains of the Duncan Dunbar and Hector have had their certificates restored, for masters and officers are all of opinion that justice is not always awarded by these official |