Democratic Sentinel, Volume 17, Number 3, Rensselaer, Jasper County, 3 February 1893 — A KNOT AND A MILES. [ARTICLE]

A KNOT AND A MILES.

How Navigators Compute Distance—- “ Dead Reckoning.*' “Will you pleaso explain the difference between a knot and a mile?'’ “What is the meaning of the term knot, as upplied to the great speed made by the City of Paris?” “19 not the term knot simply a unit for measuring the speed of a vessel at sea, and has it auytbiug to do with the actual distance that the vessel makes in a specific time?” These are only some of the questions asked by “A Subscriber,” “Constant Reader” aud scores of others whose letters arrive by each mail and each requesting a reply, some inclosing a slip of paper aud an addressed stamped envelope, some with stamps only aud mauy with neither stamps nor money, the writers having no thought that tfie answers to such correspondents involve not only expense to the newspaper of employing persons to answer these letters, but there must be added the cost of stationery, postage, etc. Some writers also neglect to givo their address, so that mauy letters cannot be answered. This latter class, no doubt, charges the editor with indifferenqe, while the fault is entirely with the writer who neglects to say to whom and where the reply is to be sent.

But wlmt is the meaning of the word “ knot ? ” It is purely and wholly a nautical term, haviug specific and direct application to the speed and distance mudo by a vessel moving in water. The word “ knot” is the mariner’s term for a nautical mile, and its use is really derived from the log-lino used by navigators of the ocean when they wish to determine the speed and the distance that the ship has probably sailed in a given time. The log-lino is an important and a very necessary part of a ship’s fittings; especially is this tho ease when, for several days at sea, the navigator is unablo because of tho sun being hidden by cl»)uds of thick weather to got a peep at it with his sextant, from which the actual position of the ship is worked out. With tho data taken by a frequent heaviug of the log (a small block or section of wood with a long line attached and run out from the stern of the vessel for a specific number of seconds) notiug the force and direction of the wind, the possible currents, or rather influences acting favorably or against the progress of the ship, the navigator is enabled to calculate very nearly, iu overcast or foggy weather, about whore Ills ship is at any hour of the day. This is called “ working out tho position of the ship by dead reckoning.”

Every one who studied the geographical table iu his curly school days will lecall that part of the sing-song recitation running like this; “CO 1-0 statute miles, or GO geographical miles equal ouo degree of lougituue at the equator.” Now, the difference between a statute mile and a nautical or geographical mile is that the latter is about BOG feet greater thau the former. There are 60 geographical miles to each degree of latitude, or to each degree of longitude at the enua tor, which degrees of miles are called “minutes" iu tho nautical vocabulary, hence the old saying “a mile a minute.” As there are #OO degrees or meridians of longitude, there are 21,000 minutes or miles in the entire circumference of the the world, at the euuutor; and it has been mathematically determined that one minute—one geographical mile—at the equatorial circle is equal to 0,080.7 feet. But it lias been the habit of mariners not to be too exact on small fractions when measuring distance ah great us a wile, consequently the practice of defiling a knqtor nautical mile us equal to 4,080 feet, instead of 0,080.7 feet, lias been generally adopted, When the nuvigator desires to make a log-line by which to ascertain tho spued mt which his vessel is making through the water,she follows the constant 6,080. Ah the number of seconds in an hour are to 6/180 feet so are the number of seconds in the time-glass (to be used) for meus-‘ uring the ship’s speed to the number of feet in each unit of measurement marked off on the log-Jine. If a half minute (GO seconds) glass hto be used, the knots must be made fiQ feet 8 inches from each other, and the number of these knots which puss from the rod over the stem while the sand is running from the top bulb to the lower bulb of the glass is equal to the number of knots or nuutical miles that the vessel would make in an hour, providing the same conditions for speed continue. For instance, if tho cn-

gines of a steamship continue to ■ make the same speed during the hour, or if the force of wind nnd spread of canvas of a sailing vussel continue the same, the number of knots on the line passing from the reel while the sand is passing through the 30-second glass, is as good an nctual measurement of the vessel’s speed through the water as could bo obtained except that the courae should bo measured by an nctual survey with instruments. If it was shown that the vessel was making ten knots, she would cover ten geographical miles, or a little more than 11$ land miles, or eleven nnd a half times 5,280 (5,280 feet being equivalent to a land mile), llcnco, to speak of the City of Paris having made 525 knots or nautical miles In 24 hours, she covers a distance of Gois land miles, as comprehended in railroad distances, or a rate of 25 land miles an hour, which is faster than many railroud trains travel. —IN. Y. Tribune.