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Miles And Knots

Miles And Knots image
Parent Issue
Day
26
Month
August
Year
1897
Copyright
Public Domain
OCR Text

Dlstances at sea are measured Ín miles, just as they are on land, but ' the speed of a ship at sea - that is, the , number of miles she makes through the water in one hour of time - is measured in knots. There is therefcre a difference in the meaning of the word "mile" and "knot;" they are no more synonymous than are the words "distance" and "speed," to which they the correlated. It is well to bear in mind, in speaking or writing of nautical matters, this distinction, that a mile is a unit of distance, but a knot is a unit of speed. There are two kinds of a mile - a statute or land mile and a nautlcal or sea mile. A statute mile is 5,280 feet. It is our standard of itinerary measure adopted from the English, who in turn adopted it from the Romans. A Roman military pace, by which distances were measured, was the length of the step taken by the Roman soldiers, aid was approxlmately flve feet long; a thousand of these paces were called in Latin a mile. The English mile is therefore a purely arbitrary measure, enacted into a legal measure by a statute passed during the reign of Queen Ëlizabeth; it has no connection with anyscale in nature. A nautical mile, on the other hand, is equal in length to one-sixtleth part of the length of a degree of a great circle of the earth. But the circumference of the earth is nowhere a true circle; lts radius of curvature is variable; henee the nautica'l mile, as a matter of fact, depends for its length upon the shape as well as the slze of the globe salled over; and henee, strictly speaking, the length of the nautical mile should vary with the latitude, from é,046 feet at the equator to 6,109 feet at the pole. Such extreme accuracy is not necessary In navigating, and can not be well attained without undue labor. The English Admiralty, therefore, have adopted 6,080 feet as the length of a nautical mile, which oorresponds with the length of one-sixtieth of a degree - or one minute of aro - of a great circle in latitnde 48 degrees. The United States coast survey has adopted the value of the nautical mile "as equal to one-sixtieth part of the length of a degree on the great circle of a sphere whose surface is equal to the surface of the earth." This givs the length of one nautical mile as eQttaJ to 6,080.27 feet, which ia very nearly the value of the Admiralty mile adopted in the English navy. Practically the nautical mile is 800 feet longer than the statute mile. In other words, one nautical mile ie equal to 1.1515 gtatute miles or one statute mile is equal to 0.869 nautical mile. Multiply nautical miles by 1.1515 and the product will be statute miles; or, multiply statute miles by 0.869, and the product will be nautical miles. A knot is in length a nautical mile- that is, 6,080 feet. But it never, correctly speaking, means anything more or less than a nautical mile an hour. When saying that a ship has a speed of twenty knots, It means that in one hour of time she can go twenty nautical miles, precisely in the way that a 2:40 horse means that a horse in two minutes and forty seconds of time can trot one mile. Remember, then, that it is erroneous to use knot as synonymous with mile; so, too, it is an error to say so many knots an hour - for the word knots alone signífies the time as well as the rate of progress of the ship during the time. Another point to bear in mind is that.though the measure at sea is called, like the measure of distance on land, a mile, like distances at sea are always measured In nautical miles, never in statute miles; and in both cases the single word mile is significant enough to convey the intended meaning. To say that the distance from New York to Southampton is 3,000 sea or nautical milea is tautological, but it would be worse still to say, as many often do, that the distance is 3,000

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Subjects
Old News
Ann Arbor Register