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THE MARINE RECORD. 2 . Correspondence. A@ 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 _ distance 178 miles, of any question affecting the interests or welfare of the lake marine should be fairly represented in THE MARINE RECORD. WORKING AN AZIMUTH. Easr Torxpo, O., January 30th, 1892. Jo the Editor of The Marine Record. In reply to ‘‘Beginner,”’ in your valuable issue of January 28th I inclose the solution of his example with a few necessary explanations, wishing at the same time to remark that his ex- ample is incomplete, as the height of eye over the lake level from which the observation was made is not given, besides, if he wants to know how the sum ought to have bore by com- pass he ought to have given longitude, as the variation on Lake Superior changed from 1 degree west at the ‘Soo’ to 11 degrees east at Duluth, in the example I haye taken 15 feet for height of eye and the variation 2 degrees east. IT am ata loss to understand the motive of ‘Beginner’? to give such a simple example for solution and can assure him that there are thousands of sailors on the lakes who can answer them correct. Try something deeper? The accompanying diagram which you may insert or otherwise explains itself and shows that the azimuth angle is situated at the zenith, as one of the angles in the spherical triangle T. P. © of which the three sides are known inserting © for complement of latitude. Then if we take Z for zenith distance. Seigiad “ P for polar distance. S for } sum of the threesides. We have by simple rules of spherical trigonometry the formula. Sine } true azimuth = V sine (S — C) sine (S — Z) sine C sine Z Latitude = 47° 01’ observed suns L. L. = 4° 50/ corrected Declination7° 9’, © L. L. = 4° 50” 00/7 Are at “ C= 42° 59” log cosecant = 0, aoe Z <3 = 0.00157 P 225. 16 112 38 Par= + 98— 69 39 log sine = 9.97201 iy ——— S-Z= 27 30 == 9.66441 4 36 06 = Osemi-dia=+16 04 19,80434:2 Otrue alt =4 52 10 log sine $ Azimuth = 9,90217 Z =8° § 3 Azimuth — 52° 58/ Troe Azimuth 105° 56’ W. Therefore “Beginner’: 's” compass Variation87°W 2 E. ought have showed it 107° 57/ — West, or West by South one- 107° 56’ half South. Frank Heyricn. THE MERCATOR PROJECTION, AsuTasura, O., February 2, 1892. To the Editor of The Marine Record. In an able article over the signature of ‘Spectator’ in your issue of January 7th., I find the present lake charts, suryey and construction spoken of in a very derogatory manner. After projecting several courses as worked out by inspection, and also by the Mercator projection, there seems to be little to grumble at in the present construction of the charts as the courses work out as they would in the Black Sea, the Baltic, or any other of our land locked waterways. This also touches somewhat our well-known friend Pearson’s theory, who hardly admits the common rules of navigation to be tenable on the Jakes. But to come back to ‘Spectator’? with his assertion that courses are intended to mislead as laid down on the charts I cannot agree. Allowing that the courses laid down on the charts are true, they work out in an air line all right as exam- ples worked from the latitude and longitude glyen in the light- house book amply prove. zs Now we all want to come up to the modern standard and use the Mercator projection if it is thoroughly proved that our charts do not practically cover that ground already. In fur- therance of this view I project a course by Mercator from Buffalo to the (Dummy) light, Point Au Pelee, so that “Spec- tator” may see it work out all right. Finding the course and distance from Buffalo to Point au Pelee Lake Erie. Lat. of Buffalo 42° 53’ N. mer P’ ’ts, 2854 tli! Pt. Pelee 41 52 N, mer p’ts, 2771 1,01. mer diff. lat. 83 345 Now with the meridional diff. of lat, 883 and the diff. of lon, 225’ I find to correspond to course S. 70° W. nearly and Again to find the course— == asthe mer. diff. lat. 1.91908 is to radius of 10.00000 so is diff. of long 2257 — 2.35218 “to taug. of Co. 8. 70° 197 W.. ——— _which is about Wby 8.38. 10.43310 | the distance— , _ Asradius == 90° = 10.00000 vi todiff. lat, 617 = 1.78533 30 piece of course 70° = 10.47260 2.25798 Lon. 78° 53/ W. Lon, 82 38 book and presume those figures are authentic, Of course this does not give magnetic or compass courses, as found by mer- cator sailing, variation and deviation should be allowed for afterwards, My question of last week ought to have read, alt. 24° 50/ instead of 4° 50/, the error was probably caused owing to my haste at the time of writing.. Brenner, FINDING AND APPLYING DEVIATION. Erte, Pa., February 3, 1892, To the Editor of The Marine Record. Replying to query of ‘Beginner’ in your issue of 28th. inst. ‘How to find the deviation and apply it correctly.’ Observe a bearing of the sun by compass fitted with circle, at same in- stant note the apparent time, and also the direction of the ships head (by the same compass) with this, the apparent time, the latitude of the place, and either the sun’s declination or the day of the month enter the table and pick out the correspond- ing time bearing, correct this for the variation, and the result will be the sun’s magnetic bearing. The difference between the observed and magnetic bearings will be the deviation of the compass on that point on which the ship was heading at the time of observation, and will be marked cither east or west according as the magnetic bearing is either to the right or left of the compass bearing. Andif you desire to make a deviation card, swing your ship’s head, say two points for each obser- vation and work out each separately as before. On October 11th., 1891, latitude 47° 01’ N. on Lake Super- ior, the longitude should be giyen because the variation of the compass in that latitude ranges from 0° to 11° also the time and the compass bearing of the sun should be given to com- plete the data necessary to find the deviation and then there will be no guess work in the matter. As for the application of deviation take your course from the chart, correct this for variation, then apply the deviation for that course; always remember that the magnetic course is to the right of the true course by amount of westerly variation and to the left for easterly. To familiar‘ze oneself with this problem take a compass card marked with the degree circle, pivot a clock hand to the center then practice with itand observe the rule above given, and you thus master the most important problem for the navigator, whether young or old. ABRAHAM J. Loucn, Pilot. WRINKLES ON “A FEW REMARKS.” Burraro, N, Y., February ae 1892. To The Editor of The Marine Record. In the issue of Tun MArtyy Recorp 28th. ult., I read the article by ‘‘Beginner’’ on A Few semarks. In reply I cannot understand why any person having the slightest knowledge of the subject under debate, can be at a loss to know how to correctly apply variation to make his in- tended port of destination, suffice it to say, that when cor- recting for variation on Lake Erie or any other lake, sea, or ocean, the rule is invariably the same, namely, westerly vari- ation allow to the right, easterly variation allow to the left of the true course to make the same, and ‘if Beginner begins to apply variation any other way he will find it necessary, and I trust in good season to begin the opposite way (to that other way.) As I understand it in this case, at Buffalo place of de- parture there is 5° westerly variation, and at ‘Toledo 0°, therefore, half the angle contained between the true and mag- netic meridians at point of departure will be the correction, which in this case is 2° 30’ to be allowed to the right of the true course to make the same good. Now in reference to Beginner’s second question on finding the deviation of the compass, and how to apply it correctly. I take it for granted that Beginner wishes someone to determine the deviation of the compass by an azimuth of the sun, al- although ie states his question in a very ambiguous and defec- tive manner, in using the altitude, latitude and sun’s decli- nation given in the example, I find the sun’s true azimuth to the S. 4° 06/ 02/7 W. or W. by S. 8S. nearly. I did not reckon on this answer from the north but rather from the south, as I never knew that Lake Superior was south of the Eqnator. Furthermore I do not know what the sun’s bearing by eom- pass was on that date and place of observation, as I was not looking at his compass or any other compass in that locality, and 1 know of no method by which the sun’s bearing by com- pass can be determined, only by observing the sun by compass, therefore I cannot tell what the deviation of his compass was from what he has given in the example, In conclusion I would ask Beginuer(as such) why did he suggest to reckon the answer from the north, or if he under- stands this simple problem of navigation why does he make use of such misleading statements as the above. But, when the deviation is determined by Beginner. or Professor, or any other nautical authority from the given example, I will state for his information that it is invariably applied the same way as the variation, and no other, whether he be on Lakes Super- ior, Huron, Michigan, Erie, or off Cape Horn, in Ashtabula Harbor, or anywhere else on terra firma, and remember, never reckon an azimuth from the north on Lake Superior. A SaiLor—on DECK. rr + An ice locomotive has just been completed at the Fishkill Landing Machine Works, at Poughkeepsie, N. Y, “It is at- tracting considerable attention, GRAPHIC METHOD FOR FINDING DEVIATION. BY JOHN MAURICE. With reference to the previous article treating of the mag- netic forces, the solution is as follows: Draw a straight line of the length of 100 parts from a con- venient scale. This line representing the magnetic meridian, measure as many parts as represent 100 G. from the north end of the line to the other end, and make the point thus found the center of a compass dial with its north in the Magnetie meridian. Constructor put a similar compass dial on the other end of the line with its center in the termination point, and its north coinciding with the magnetic meridian. Fur- ther, construct a circle to the diameter of 100 G. through the center of the first mentioned compass dial and the north point of the line. The first, or northerly compass card serves to indicate ,the magnetic course the vessel is successively headed on, That part of the course line within the circle to the diameter 100 G., represents always the magnetic force from induced magnetism, for the magnetic course the;vessel is headed on; and the intersec- tion point with the circle is always the starting point from which the magnetic force 100 B. is measured off; which when positive is set off on the course line in the direction of the ship’s head, but when negative in the opposite direction. From the termination point of 100 B., is to be set off at right angles 100 C. by the original scale; to the right when positive, and to the left when negative; right and left being determined by looking in the direction of the ship’s head. From the end of 100 C., a line drawn to the other compass center shows on that compass the north-south line of the ship’s compass, and with reference to the magnetic meridian, the deviation. A square on which 100 B. and 100 ©. are marked off, placed on the magnetic course with the point indicating 100 B., al- ways in the periphery of the circle, and a protraction or card from the compass on which the deviation is read off, are con- venient means for ascertaining the deyiation on any course with facility. Not to be confounded it is well to mark on the square the direction of the ship’s head. The deviations thus found refer to magnetic courses. Conversion of magnetic courses into compass courses, and vice versa by the method of parallel scales. Make of two parrallel lines about an inch apart a scale of 128 equal parts of convenient size, each part representing } point. One line on the scale is for compass courses, and the other for magnetic courses. Courses are to be marked in the consecutive order as they appear on the compass, beginning with north over east. For every magnetic course set off the deviation from the line marking the courses on both scales, to the right when east, and to the left when west; and from the point thus found on the other scale draw a straight line to the magnetic course for that point. Two such lines for two adjacent courses continued, intersect each other in a certain point. From this intersection point a line drawn to any point contained within the limits of the two lines mentioned intersects both scales, and thus fur- nishes the corresponding values on each scale. In the vicinity of the course, for wh’ch the deviatiou attains a maximum, a kind of nentral zone will be left, indicated by two nearly par- allel lines, within which zone a line parallel to the former, marks the corresponding values on both scales. Thus by means of the intersection points mentioned aboye, the corresponding values for all courses are easily found. + oo NORTH. MAGNETIC POLE. An expedition will start north about May Ist. on a three years’ trip, with a view of re-locating the north magnetic pole and to make magnetic and other observations, The scheme of work to be done will be prepared by a committee of the National Academy of Sciences and the expert magnetists of United States Coast aud Geodetic Survey, and the observers and instruments will be furnished by the latter bureau. It is now 60 years since Sir James Ross located the north magnetic pole on the west coast of Boothia Felix, which land was named after Sir Felix Booth, who furnished the funds to equip the expedition, An expedftion haying in yiew the ac~ complishment of such valuable scientific results and under the auspices of the National Academy of Sciences and the United States Coast and Geodetic Survey will attract the attention of scientific bodies all over the world, and the names of those whose liberality has made the echieyement of such yaluable results possible will be linked with one of the greatest enter-— prises of the age. The great expense of the expedition (the cost of instruments and the pay of observers) will be borne by Pies the Coast Survey and the Signal service, and it only remains to provide for the transportation and maintenance of the party — during its three years of labor there. The portion of the ex- pense to be borne by private subscription will, therefore, BOR exceed $20,000, or $25,000, f, The route of travel is by whaler to Repulse Bay, the ak northerly portion of Hudson’s Bay, where a permanent sta-— tion will be established. ‘This is the nearest point to the mage netic pole of Ross that can be reached by vessel. — station at Repulse Bay summer expeditions will be sent with sleds to the pole-containing area, Ross’s Poe bei si about 300 miles. From the rr es ce Iv is about time the Behring Sea Conference: red. Sealers are fitting Be a bait.’”