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. THE MARINE RECORD. v4 Correspondence. 8a- We do not hold ourselves responsible in any way for the views or opinions expressed by our correspondents. It is our desire that all of any question affecting the interests or welfare of the lake hould be fairly represented in THE MARINE RECORD. MERCATOR PROJECTION THE BEST. 4 Derrort, February 16th, 1892. “Beginner,’”’ Ashtabnla, has on several occasions given the readers of Tur Martne Record some questions to solve, though in finding the course from Buffalo to the Dummy at Point au Pelee by reckoning; he takes the Jongitude of Pelee Island light for the longitude of the Dummy, never minding an overland passage of 4 or 5 miles on Long-Point Island. By this ingenious letter he thinks to prove, that no Mercator charts are necessary for lake navigation. As he obviously compounds the finding of a course by reckoning, with the find- ing of a course by compass dials on the chart; it has escaped his notice, that, whatever the course from Buffalo to Pelee may be, the course at Buffalo is}found in the lake charts } point more northerly than at Pelee, on account of the conical projection on which the charts are drawn. Such errors in courses are impossible in}Mercator charts; and as the avoiding of errors is of prime necessity in navigation, lake charts ought to be on Mercators projection. Mr. Frank Henrich and others has taken the pains to show “Beginner’’ how such problems as azimuath’s are easily solved. From a general point of view, the method used by Mr Henrich rust be given the preference to any other, as by it, azimuths in north latitude are reckoned from north, and in south latitude from south, being easily remembered and not liable to mistake. The method to which ‘A sailor on deck” refers is in general use in the British navy, reckoning azimuths from south in north latitude and from north in south latitude. Both methods are in effect the same, the only dif- ference consists in writing down the angle from the table. If for sine } A is substituted co-sine 1g A and the angle for sine 3g A— 52° 58/ the angle for cos. } A= 37° 2’ or (90°—52° 58’) consequently A—74° 4’ from south, equal to 105° 56/ from north, or twice 52° 58’. By the first method the angle at the zenith in the spherical triangle between sun, pole and zenith is found; by the second method the outer angle sup- plementing the former to 180° is found. Sprcrator, EDD oo PRACTICAL APPLICATION OF THE SHORT HAND AND GRAPHIC METHOD. BY JOHN MAURICE, In Tue Martyr Recorp of December 3ist, 1891, Mr. Louch presents an extract from his log book as pilot of the U. 8. S. Michiganin 1885, whichis a valuable basis for the present illustration. Arranging his figures in a table so as to facilitate review we have: From these figures it is evident thata mistake! must be in the deviation Comp. Co. Dev. Comp. Co. | Dev. | N 38° 6 E/13°W for the courses $2°.8 W, N 46° W | 12°F) — tes and 82°.9W.thedevia-| — | — | NGI7E 23W .tion differing 143°. It) g50 Ww | 26E ais’ | re appears further, that a) — | — S38 E |27w small error existsin the) S2-8W 2.5 W| — | — deviation for N64.7 | S23W | 12E) — = and N 67°.5 E. Leaving these errors out of account, and con- sidering the figures for the other courses to be correct, there remain four observations in the vicinity of the four quadrantal points by which we are enabled to find the magnetic forces of the vessel, and thus the deviations for all courses. As the observations are not exactly on the quadrantal points, we must make some allowance for that, before commencing to figure, by correcting the values as far as possible, where neces- sary. For the course N 38°.6 E the correction with reference to the deviation for N 64°.7 E and N 67°.5 E is found by in- terpolation to be about 2°, therefore, the deviation for NE will be nearly 15° W. For NW we have 12° E; and for SW and SE the change in the deviation is so small on account of the deviation being a maximum in the vicinity, that no cor- rection may be required. hus the observed values are: NE — 15°, SW 26°, SE — 27°, NW 12°, and the solution is as follows: B=ier4 wo — —0.44 2%6X}= 2 19.5=10G C=4ar= —0.01 G = 0,195 From these figures follows that the force from induced mag- netism is of the general order, but the force from permanent magnetism exceeds the ordinary average considerably, being nearly equal to half of the earth’s horizontal force. The signs of B and C indicate, that the ship’s polar force, that is its South pole, is located with reference to the ship’s compass towards the stern, in that quarter of the yessel which is port, and very near the midline of the ship. With the magnetic forces thus found the following devia— tion table for the U.S. 8. Michigan is obtained by swinging the vessel, as it were, on paper, using the graphic method ex- plained in the former article:— Mag. Co. Mag. Co. Dev. P'ts. N N | +W N by W iB NbyE | ae NNW $E NNE Lar NWbyN 1, E NEbyN | Tp NW 1p E NE } 1} N Wby W at NEbyE a WNW Qh ENE ay W by N 2p Eby N Qh Ww 2p E oh W by S 24 fe Eby S 24“ WSWw Qh « ESE ae SW by W moe SE by E 14“ SW 1p « SE 1g « SW by S 1p SEbyS 14“ SSW gf SSE seks S by W }E S by E Pag by} — Ss _— From this table, referring to magnetic courses, is obtained the following table, by means of the method of parallel scales: Comp. Co. Dey. P’ts. Comp, Co. Dev. P’ts. N —W N —W N by W }E Nby E ge NNW race NNE ge N W by N ra N Eby N 1“ NW ih“ NE 4 N W by W 14“ NE by E 13 WNW 1h“ ENE bag W by N ese E byN wanes WwW DE E 2g W byS a4 E by S Qh Wwsw 24 «° ESE 2g « SW by W Op S Eby E OR « SW ay SE ay 8 WbyS eyes SE by § 2 « SSW 1g « SSE 14 S by W iE Sby E iW 8 _— 8 = obtained from this table, we have:— Deviations. 1 Deviation. Comp Cal Obs. I Gra. Ma|@°™P Co! by Obs. \by Gra. Md 2 sn — |N386E] 13W | 13 W N 46 wi RE | 45 Ee = = = as — |N647E) 23 w | 20W = ae — |Ne675E| 20W | 21W s5ow| 298 | 27 gee aerate = Es a — |s3sE| aw | 24W $2.8W\2,5W)| 2 lees ed = S23WliZE § |... ne oa = From which it appears, that the observed East deviations near the quadrantal points are too small and the West devia- tions too large, as if the compass was affected by a constant deviation of from 2° to 3° West. But, as the observations on the courses N 64°.7 E and N 67°.5 E show some small differences both ways, it is uncertain whether there was a constant devia- tion or not. The remaining differences, Mr. Louch is per- haps able to explain away, that his certificate as lake master may be changed from ‘‘excellent’* into ‘‘unsurpassed ” ED oa COLORS NAILED TO THE MAST, Wasurnctoy, D. C., February 18, 1892. To the Editor of The Marine Record. Noting that you have been deceived by the enemies of the American ship that are now carrying high sail in Washington, into incorporating their lies in a short notice of my resignation as Commissioner of Navigstion, I desire to say to my old friends, readers of your journal, that there is not a word of truth in the following statement: “Mr, Bates made the blunder of giving out his annual re- port for publication, before it had been submitted to the Sec- retary of the Treasury. In the report he went out of his way to discuss the tariff, reciprocity, and other economic questions with an independence that was refreshing.’’ I sent you a clipping from the Washington Star (or a paper) a few days ago in which certain other lies were denied, which I hope you will publish. Briefly, in my forced resignation the friends of an American merchant marine haye sustained a de- feat at the hands of paid agents of the foreign steamship com- panies, their corrupted dupes in office, and the dirty scheming politicians combined. No true man can serye with enemies and spies, and long maintain his place, This is the philosophy of the difficulty. Yours truly, William W. Bates. oo AN. EXPANSION OF THE CURVE. Burrauo, N. Y. February 15, 1892. To the Editor of The Marine Record. . Referring tomy answer in your issue of 4th inst., in reply to “Beginner’s’’ question or example, it should read S 74° 06” 02/’ W, or W by S {5 nearly, instead of S 4° 06/ 02’ W, or W by S§S nearly, which appears in your issue of 4th inst. I cannot understand how that mistuke occurred as I haye a copy of the original before me; however, the course converted into points, corrects the above to any intelligent mind, as W by S §5S nearly, reads S 74° 06’ 02’” W which is one and the same. Also I observed ‘‘Beginner’s” correction to the Alt. and if the example was worked out by Alt. 24° 50/ instead of 4° 50/ it would undoubtedly give a different result, but withal, I can- not for the life of me determine the deviation of his compass by his example, and should he or anyone else accomplish it by this unknown rule (to the nautical fraternity) I should like to see it. Isay again it is invariably applied the same way as it always was. Now Mr. Editor, I am no aspirant to the title of eritie or crank, but merely a plain, every-day son of Neptune. I have counted the number of stars in the Southern Cross, been to Tonawanda, Ashtabula, passed Pelee Spit and Light (Lake Erie) oftentimes, and sailed up and down from Buffalo to Chicago no less than sixteen times last season, but I never knew the distance between Buffalo and Pt. Pelee to be 181 miles, as given by ‘‘Beginner’’ in his example, calculated by Mercator’s sailing. How he found it to be so much, [ do not know, there- fore I think that Mercator’s projection must have stretched more than any lawyer’s conscience, if there are 181 miles be- tween Buffalo and Pt. Pelee. By none of the known methods can ‘Beginner’’ or I make it such, and if ‘Beginner’ ever was on his nautical nut, I am seriously mistaken if he did not fall off when the expansion of the curve took place. Don’t go fault-finding with the charts, admitting that they are more or less defective, still the chart of Lake Erie will vindicate itself in relation to this example, but I will not vouch for the Lighthouse Book. “A Sarmor on Deck,’” a oe TERRESTRIAL MAGNETISM. (By Henry Winpe F. R. 8.) For a half centary the science of Terrestrial Magnetism has been laboring under the burden of knowing no theory or work- ing hypothesis that held out the least promise of correllating the heterogeneous mass of facts observed in all parts of the world, a statement that could hardly be made of any other important branch of science. Many volumes of observations upon the magnetic force and the movements of the magnetic needle have been produced, and yet with a feeling of discouragement, for lack of a plan upon which to arrange them. Were it not for the obvious advantages to navigation, the needs in connection with geodetic surveys, the suspicion that meteorology might have something to do with it, and the irresistible scientific in- stinct that every force in nature must be accounted for; the de- pression would have been overwhelming. * * * The most ancient, as well as the most interesting obserya- tion of the declination in the North Atlantic, is that made by Columbus on thez13th of September, 1492, when he observed the needle to pass from the E. to W. of the meridian in latitude 28° N. and longitude 28° W. Now, it is on record that as Columbus advanced westward from the Island of Ferro, he was amazed to find the third day after his observation of the variation, and when abont 300 leagues west of Ferro, that the needle again pointed to the pole star.) Historie del S. D. Fernando Colombo.—In Venetia, 1571, Chap, 17.) Onur author proceeds with a wealth of illustrations of agree- ment extending over such vast regions of the earth and such long ranges of time, descending to minute details usually, as to preclude the possibility that there is anything wrong with his general analysis. He concludes that the period of a complete rotation of the fields relatively to one another is 960 years, and not 648 years, as magnetic tradition has it, the 960 year period also agreeing with Sir. W. Thomsou’s value as given ina recent volume of reprints. The sea-areas are more highly magnetic, by reason (1) of the permanent low temperatures at the bottom of the ocean, which is favorable to high magnet ism, and because shielded from the fluctuations of tempera- tare caused by the heating and cooling of the land in diurnal and annual periods; and (2) by the fact that the ocean beds are thicker than the land areas, and therefore contain more of the ferruginous iron ore. The secular variations of the magnetic meridians show that they pass quite smoothly over wide ocean or over wide land areas, but that they appear to hang along the coasts, where the break or faulting seems to produce greater polarity along the north and south lines. The Amer— ican north magnetic pole is, as it were, held or retarded in its recessional march westward by the permanent magnetism stored up and retarded by the cold and uniform conditions of temperature prevailing in that region. It will finally break loose and hasten to take up its place along with the more freely moving lines. From the various movements of the declination and inclina- tien needles, correlated with each other in time, direction and amount, on different parts of the.earth’s surface, the theory of a fluid interior may now be considered to be as firmly estab- lished as the doctrine of the diurnal rotation of the earth on its axis,” p. 31. This reads in marked contrast to the words of Sir W. Thomson in the Treatice on Nat, Phil. If, p. 480 and p. 485, which says, ‘The earth, although once all melted; or melted ail around its surface, did, in all probability, really become as solid at its melting temperature all through, or all through the outer layer, which had been melted; and not until the solidification was thus complete, or nearly so, did the surface begin to cool;’’ and, ‘regarding the present conditions of the earth’s interior, it is not, as commonly supposed, all liquid within a thin solid crust of from 30 to 100 miles thick, but it is on the whole more rigid, certainly, than a continuous solid globe of glass of the same diameter, and probably than one of steel, Inasmuch as magnetism is in reality founded upon the same Newtonian law as the force of gravitation, we may expect it to go hand in hand with that fruitful aspect of the law, ia un- folding the secrets of nature. If this is so, then also the indica- tions will not be misleading, that terrestrial magnetism is rapidly emerging from that helpless condition in which it has so long been hindered from fulfilling its true mission in the service of science. 3