Most maps of the world show lines that are not on the Earth's surface.One line is the equator(赤道)．It is an imaginary line around the widest part of the Earth.There are similar lines both north and south of the equator.These circles become smaller and smaller toward the north pole and the south pole.These lines, or circles, are parallel(平行的)—meaning that they are equally distant from each other at any point around the world.These lines show what is called latitude(纬度)．

       A navigator can know the latitude of his ship by observing the location of stars, where the sun rises in the morning and sets in the evening, and what time of year it is.With this information he knows where his ship is in relation to the north or south pole and the equator.

       Still, there is one more important piece of information necessary for safely sailing the oceans.For many centuries, scientists, astronomers and inventors searched for a way to tell longitude(经度)．The lines of longitude go the other way from latitude lines.They stretch from the north pole to the south pole, and back again in great circles of the same size.All of the lines of longitude meet at the top and bottom of the world.

       To learn longitude at any place requires knowledge about time.A navigator needs to know what time it is on his ship and also the time at another place of known longitude—at the very same moment.

       The Earth takes twenty­four hours to complete one full turn or revolution of 360 degrees.One hour marks one twenty­fourth of a turn, or fifteen degrees.So each hour's time difference between the ship and the starting point marks a ship's progress of fifteen degrees of longitude to the east or west.Those fifteen degrees of longitude mark a distance traveled.

       At the equator, where the Earth is widest, fifteen degrees stretch about one thousand six hundred kilometers.North or south of that line, however, the distance value of each degree decreases.One degree of longitude equals four minutes of time all around the world.But in measuring distance, one degree shrinks from about one hundred and nine kilometers at the equator to nothing at the north and south poles.

Notes：

①navigator n ． 领航员　②stretch v ． 伸展

                                                                                        A Manhattan Crossing

       New Yorkers like to say they can walk faster than the crosstown bus.On 34th Street, buses average about four miles an hour.For those in a hurry, pretty much everyone here, it's an icy pace for a crosstown trip.Janette Sadik­Khan, the city's transportation commissioner, is proposing an interesting fix for 34th Street.

       The city plan would close 34th Street to non­bus traffic in the block between the Empire State Building and Macy's.On the rest of the street, cars would move one way only.It would take getting used to, but for bus passengers, the city says there are more than 40，000 a day on public, tour or commuter(通勤者)buses along 34th Street.The plan should cut the commute by up to 35 percent.

       People in other vehicles or about 10 percent of the human traffic would have to zig and zag(锯齿形)to get through this section of the city.It is probably fair to say that most are not particularly pleased about the whole concept.

       So the city needs to answer important questions.Will this unrest mean more traffic on side streets that are already unbearably crowded？Will deliveries be limited to the daybreak hours？Will Mayor Michael Bloomberg and Ms.Sadik­Khan be willing to change or drop the plan if it simply won't work?

        The Bloomberg administration has worked to improve bus traffic around the city.An experiment to speed up city buses along Fordham Road in the Bronx has already reduced travel time and increased passengers' number.

        Urban planners have been studying the city's crosstown problems since the first traffic jam.Robert Moses at one point proposed a major highway just south of 34th Street, part of which would go through an office building.The question is still whether it will really make it easier to operate in Manhattan.

Notes：

①unrest n ． 动乱，动荡　②concept n ． 概念