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JO THE MARINE RECORD. GORRESPONDENGE. 8@-We do not hold ourselves responsible in any way for the views or opinions expressed by our correspondents. It is our desire that all sides of any question affecting the interests or welfare of the lake ma- . tine should be fairly represented in Toa Marine Recor. HOW MANY RHUMB-LINES? To the Editor of The Marine Record: ‘Your friend, in replying to my communication of April 2, seems to be at a loss as to what I mean by the term ‘‘rhumb-line,” and comes to the conclusion that I recognize. more than one kind. He is informed—if he does not already kuow it—that there are 'two kinds of rhumb-lines, one of which he has been kind enough to . define for us, and which, for the sake of designation, we will call the geographic rhumb-line, and the other we will call the magnetic rhumb-line. This latter line is a track of a ship made by steering on a constant coim- pass course. This course, being effected by the change of variation, would make the ship cross the geographic meridians at a varying angle, though the reading of the compass card remain constant. The ‘geographic rbhumb-line’’ is the theoretic course of ship, and though it is the correct course, no ship ever sailed on it, but always on the magnetic rhumb, which is always more or less divergent from the true or geo- graphic rhumb; and it is the failure of the general pub- lic to recognize the two kinds of rhumb-line that has raised this discussion. Our friend informs us that in order to follow the rhumb-line the navigator must change his compass course frequently to compensate for the change of vari- . ation, and here it should be remarked that on the lakes no other than the rhumb-line course is known. It was to the end that some means might be suggested for keeping ship more clearly on her course than can be done by the instructions on our charts, good as they are, that I have started the discussion of this question, and it gives me pleasure to have one so competent as my critic appears to be pronounce the method that I suggested in the issue of April 2, and illustrated in Fig. - 8 of that paper, as ‘‘clear and acceptable.” My fullest ambition in that direction is now gratified. I know that if it should be adopted it will give entire and satis- factory relief in the difficulty mentioned, and without something of the kind our ships are liable to get badly _off their course. Our friend is at aloss, or badly out in comprehend- ing my illustration of the reason why the two rhumb- lines, z.¢., the ship’s track and the geographic rhumb- ' line cannot agree. Perhaps Iam remiss in n t making the thing as plain as it should be, inasmuch as the idea is somewhat new, and another reason for his embarrassment is in the fact that he fails to recognize that while there are two kinds of rhumb-lines there are also two kinds of card motion also to be considered. Thus, if on any latitude we sail, _ say due west, then, in order that our geographic card _ may always have its zero point to the north, as it must in order that we may sail due west, it must swing ' to the right through an angle equal to the inclination _ of the meridians between which we sail for that latitude. This motion for any latitude is strictly uniform, vary- ing with the difference of longitude. But not so with the motion of the magnetic card, which is only variable, so that strictly the change of variation is not the full motion of the same, as is generally supposed, and as supposed in my illustration, but the difference of the i motion or swing in azimuth of the two cards. The fundamental idea is, that in order that the two rhumb-lines may coincide the swing or motion of the _ azimuth when referred to the initial meridian must be _ strictly the same. With this interpretation of the con- ditions stated, I think there will be no trouble in com- prehending the manner of my text. There is a small areain the North Pacific, central in about latitude 20°, where the motion of the two cards is very approximately equal; this condition is indicated _by the isogonic curve running nearly ona parallel of latitude. Here, of course, the two rhumb-lines will nearly coincide, but in nearly every other point of the navigable part of the globe, the magnetic rhumb will diverge from the geographic rhumb to the right or left. With regard to his illustration of what he calls my error in»regard to the magnetic pole, he is peculiarly unfortunate. By his two spherical projections con- s'‘ituting his Fig. 3 he gives what he calls the true idea of maynetic meridian and the magnetic pole, first giv- ing a definition of the magnetic pole entirely different from that which I gave and which I disputed. The ideas he gives are chiefly those of Gauss, who deduced the place of the pole approximately, which afterwards, in 1831, was found by Capt. Ross, but some- whatto the south and west of the place indicated by Gauss. At the time of the discovery by Ross this pole was supposed to be a center governing the direction of the needle in the surrounding country, and indeed in the whole hemisphere. Accordingly Duperrey, partly trom fact and partly from fancy, constructed what he called asystem of magnetic meridians, connecting opposite magnetic poles, almost precisely as represented in Fig. 3 of the iliustrations published April 23. But these theorists soon found themselves ahead of the times. This pole found by Capt. Ross was only a pole of max- imum magnetic intensity, which might be called a dynamic pole, and not at allinasense of having con- trol over the direction of the needle in remote parts of the hemisphere. Besides, there were other poles of almost the same intensity in this hemisphere. But the sorriest thing about the illustration of our friend is its wide departure from facts. From the interior of South America, in latitude about 15° south, longitude about 60° west, to the interior of British America in latitude, say, 60° north, longitude 90° west the illustrations by the meridian show a westerly variation; whereas, by actual surveys the variation is known to be easterly every rod of the way. The definition of a magnetic meridian, as shown in our friend’s illustration, is given by Duperrey, is such a line as would be traced by traveling in the direction indicated by the compass needle, from one magnetic pole to the other. The unfortunate thing about this definition is that no two pairs of meridians ever con- verge to the same point, asdo the geographic meridians, as a consequence no such pole has ever been found, nor will such a pole ever be found. Again, the illustration of Fig. 3 shows meridians con- -verging to the dynamic pole discovered by Ross, with almost the same regularity as the geographic meridians converge to the geographic poles. Now, the well known fact is that there are absolutely no intersection of converging meridians at this dyna- mic pole froin points at any considerable distance. The nearest intersection being say 300 miles away, and up to 2,000 miles, mostly to the east and north. (See chart of Magnetic Declination for 1885 by Otto J. Ktobz.) The one simple law referred to in my paper, by which a small magnetic field may give direction toa magnetic needle in spite of a larger field more remote, disproves beyond a possibility of refutation, the possibility of a single point or pole giving direction to the needle in the whole hemisphere. With regard to the bill for navigating the lakes by a trolley line, as proposed by our long time friend, Capt. John Swainson, I think it will have to go over till another Congress more efficient than the one in ses- sion now. It takes them too long todoa thing quickly. And with regard to his criticism of my remarks con- cerning the failure of our new chart to meet one par- ticular of our wantsI would have looked for a better shot than he made. What he called errors, or referred to as such, are not errors at all, and at worst could only be called a deficiency, and even this I excused by lay- ing the trouble to a peculiarity of our locality. Hope friend Swainson will take better aim next time. H. C. PRARSONS. Ferrysburg, Mich., May 2. A PROGRESSIVE MARINE INDUSTRY. To the Editor of The Marine Record: It isalways pleasant to note a marked progress in any line of marine industries, and while the greater interests of ship and engine building, boiler making, steam wind- lasses and steering gears of various and improved types, etc., etc., are duly heralded through the medium of the trade press, it is directly within the province of the RECORD to pay a well entitled tribute to printers’ ink as demonstrated in the increased volume and improve- ment of contents contained in the Beeson Marine Direc- tory for the current year. Not only is the publication enhanced beyond the last of any preceding annuals but the enterprising publisher has added a fully equipped ty pe-setting plant to his well-established business, s 5 that in the future the work of compiling, as also the com- position of the marine directory in all its branches wil be carried on in one of the most select, centrally located and convenient buildings in the city of Chicago. In viewing the annual progress made in this techni- cal publication during the past ten years, too much credit can not be given to the well directed energy and business aptitude of its author and proprietor, Mr. Harvey C. Beeson, who has brought the work along from almost insignificant proportions up to a pretentious cloth bound volume of over 400 pages.and made it a standard au- thority on the matters of which it treats, so that it may now be candidly stated that in so far as material and technical advancement is concerned, as well as the im- proved adaptation of printers ink, there have been no more advanced strides made in this industry than can be observed in the current annual editions of Beeson’s Marine Directory, a work, by the way, which is univer- sally acknowledged as beiig a positive necessity to all interested in maritime offices on the lakes. During a recent visit your correspondent was highly pleased to be shown through the well-equipped and or- derly kept printing rooms of the directory, where ajl hands were apparently intent upon the work of setting up the various portions of this marine publication un- der the efficient management of Mr. ‘Thos. Morris; and later, on a visit to the handsome offices of the proprie- tor in the Royal Insurance Building, where the sev- eral vessel clasifieation registers and technical works, as well as the daily papers fromthe more important lake ports were to be found on file and kept chiefly for refer- ence and the ccnvenience of callers and visitors from out of town connected in any manner with the marine interests. Capt. J. SWAINSON. Ol EEE ss a TRADE AND INDUSTRIAL NOTES. The Lunkenheiner Co., of Cincinnati, New York, and London, have issued a very fully illustrated pocket cat- alogue of their various types and: styles of valves, oil cups, spray-feed and sight-feed graphite lubricators, etc. Copies of this catalogue will be sent free upon request. ; : It is very important to have a windlass so made that the wild cat or chain wheel and the shaft shall be sup- ported solidly by a bearing. Otherwise the windlass is liable to break when snubbing the chain suddenly, or in an emergency; also when riding at anchor in heavy weather. In the ‘‘Providence’’ windlass as made by the American Ship Windlass Co., of Providence, R.I., the wild cat is placed close to the side bitt and in con- tact with it, sothat the wild cat and shaft are solidly supported. The shaft is of the full size and is not weakened by cutting a thread in the shaft, as in some other styles. hese are very important matters to ship owners, and thesetwo little items will oftentimes prove of more value than the whole cost of the windlass, but every point of the ‘‘Providence’’ machine is looked after and has been perfected by a study of over forty years in practical use. Thee F. S. and J. D. Negus’ Nautical Almanac has reached the fifty-seventh year of its publication, and while pub- lished primarly for the benefit of ships entering New York and those engaged in the coasting trade, it is found by many lake masters to contain much that is of great service to them throughout the year. The calen- dar gives the sun’s apparent declination and the equa- tion of time, and contains a blank log for the entire year. The almanac is virtually a coast pilot for the Atlantic coast, and this year’s edition contains the in- ternational ‘‘Rules of the,Road at Sea.’’ The RecorD see that it is sent toany master on receipt of 20 cents to pay postage. Charles Potter, optician, No. 31 King street, east, Toronto, Ont., has just issued a large cat- alogue of his optical and mathematical instruments, including many goods of service on shipboard. Mr: Potter’s business has been established over 40 years. _—_—_—_ nn ca A correspondent of the Army and Navy Journal pays the following tribute to Col. Jared A. Smith: ‘Colonel — Smith has saved the government thousands of dollars” by his ceaseless care for and personal attention to. ithe multifarious public work under his charge. As a’gen- tleman and citizen he has no peer. His patient court: esy, generous kindness, just and honorable treatment, have won the respect, friendship, good will.and gratit- — tude of every person, whether business men or em- ployes, who have had the good fortune to come.in con- tact or transact business with him during his long, hon- orable and most useful army service.”’ ae ee