One of the early advocates of uniform time was a Connecticut chool teacher, Charles Ferdinand Dowd. Dowd lectured railroad ›fficials—and anyone else who would listen on the need for a tandardized time system. Since the continental United States covers approximately 60 degrees of longitude, Dowd proposed that he nation be divided into four zones, each 15 degrees wide-which Is the distance the sun travels in one hour. With the prodding of Dowd and others, the railroads adopted in 1883 a plan that provided for five time zones-four in the United States and a fifth covering the easternmost provinces of Canada.

The plan was placed in operation on November 18, 1883. There was a great deal of criticism. Some newspapers attacked the plan on the grounds that the railroads were "taking over" the job of the sun," and said that, in fact, the whole world would be "at the mercy of railroad time." Farmers and others predicted all sorts of dire results-from the production of less milk and fewer eggs to drastic changes in the climate and weather-if "natural" time was interfered with. Local governments resented having their own time taken over by some outside authority. And so the idea of a standard time and time zones did not gain popularity rapidly.

But toward the end of the second decade of the 20th century the United States was deeply involved in a World War. On March 19, 1918, the United States Congress passed the Standard Time Act, which authorized the Interstate Commerce Commission to establish standard time zones within the United States; and at the same time the Act established "daylight-saving time," to save fuel and to promote other economies in a country at war.

The United States, excluding Alaska and Hawaii, is divided into four times zones; the boundary between zones zigzags back and forth in a generally north-south direction. Today, for the most part, the time-zone system is accepted with little thought, although some people near the boundaries still complain and even gain boundary changes so that their cities and towns are not "unnaturally" separated from neighboring geographical regions where they trade or do business.

The idea of "daylight-saving time" has roused the emotions of both supporters and critics—notably farmers, persons responsible for transportation and radio and television schedules, and persons in the evening entertainment business-and continues to do so. Rules governing daylight-saving time have undergone considerable modification in recent years. Because of confusion caused by the fact that some cities or states chose to shift to daylight-saving time in summer and others did not-with even the dates for the shifts varying from one place to another-Congress ruled in the Uniform Time Act of 1966 that the entire nation should use daylight-saving time from 2:00 A.M. on the last Sunday in April until 2:00 A.M. on the last Sunday in October. (Actually "daylight-saving time" does not exist: there is only "standard time" which is advanced one hour in the summer months. "Daylight-saving time" has no legal definition, only a popular understanding.) Any state that did not want to conform could, by legislative action, stay on standard time. Hawaii did so in 1967, Arizona in 1968-(though Indian reservations in Arizona-which are under Federal jurisdiction-use daylight-saving time) and Indiana in 1971. In a 1972 amendment to the Uniform Time Act those states split by time zones may choose to keep standard time in one part of the state and daylight-saving time in the other, Indiana has taken advantage of this amendment so that only the western part of the state observes daylight-saving time.

When fuel and energy shortages became acute in 1974, it was suggested that a shift to daylight-saving time throughout the nation the year around would help to conserve these resources. But when children in some northern areas had to start to school in the dark in winter months, and the energy savings during these months proved to be insignificant, year-around daylight-saving time was abandoned, and the shifts were returned to the dates originally stated by the 1966 Uniform Time Act. In the long run the important thing is that the changes be uniform and that they apply throughout the nation, as nearly as possible.

The whole world is divided into 24 standard time zones, each approximately 15 degrees wide in longitude. The zero zone is centered on a line running north and south through Greenwich, England. The zones to the east of Greenwich have time later than Greenwich time, and the zones to the west have earlier times-one hour difference for each zone.

With this sytem it is possible for a traveler to gain or lose a day when he crosses the International Date Line, which runs north and south through the middle of the Pacific Ocean, 180° around the world from Greenwich. A traveler crossing the line from east to west automatically advances a day, whereas one traveling in the opposite direction "loses" a day.

Both daylight-saving time and the date line have caused a great deal of consternation. Bankers worry about lost interest, and law suits have been argued and settled-often to no one's satisfaction on the basis of whether a lapsed insurance policy covered sub

TIME INTERVAL-LOCAL

SYNCHRONIZATION

REGIONAL

DATE-UNIVERSAL

TIGER

stantial loss by fire, since the policy was issued on standard time and the fire in question, had it occurred during a period of standard instead of daylight-saving time, would have been within the time still covered by the policy. The birth or death date affected by an individual's crossing the date line can have important bearing on anything from the child's qualifying for age requirements to enter kindergarten to the death benefits to which the family of the deceased are entitled. The subject continues to be a lively issue, and probably will remain so.

TIME AS A STANDARD

The disarray in railroad travel caused by the lack of a standard time system in the late 19th century illustrates one of the primary benefits of standardization-standards promote better understanding and communication. If we agree on a particular standard of time or mass, then we all know what a "minute" or a "kilogram" means.

In working with time and frequency, we have standardization at various levels. With the development of better clocks, people began to see the need for defining more carefully the basic units of time since the minutes or seconds yielded by one clock were measurably different from those yielded by another. As early as 1820, the French defined the second as "1/86,400 of the mean solar day," establishing a standard time interval even though town clocks ticking at the same rate would show different local timethat is, a different date for each town.

In our first chapter we discussed briefly the concepts of time interval, synchronization, and date. In a sense these three concepts represent different levels of standardization. Time interval has a kind of "local" flavor. When one is boiling a three-minute egg, the time in Tokyo is of little concern to him. What he needs to know is how long three minutes is at his location.

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Synchronization has a somewhat more cosmopolitan flavor. Typically, if we are interested in synchronization we care only that

particular events start or stop at the same time, or that they stay in step. For example, if people on a bus tour are told to meet at the bus at 6:00 P.M., they need only synchronize their watches with the bus driver's watch, to avoid missing the bus. It is of little consequence whether the bus driver's watch is "correct" or not.

The concept of date has the most nearly universal flavor. It is determined according to well-defined rules discussed on page 67, and it cannot be arbitrarily altered by people on bus tours; they do it only at their own peril, for they may well be late for dinner.

There has been a trend in recent years to develop standards in such a way that, if certain procedures are followed, the basic units can be determined. For example, the definition of the second, today, is based upon counting a precise number of oscillations of the cesium atom, as we discussed on page 66. This means that anybody who has the means and materials necessary, and who is clever enough to build a device to count vibrations of the cesium atoms, can determine the second. He doesn't have to travel to Paris. Similarly, the unit of length is defined by a certain wave length of light emitted by the krypton atom.

Concepts such as date, on the other hand-built from the basic units have an arbitrary starting point-such as the birth of Christ which cannot be determined by any physical device.

IS A SECOND REALLY A SECOND?

In our development of the history of timekeeping, we saw that the spinning earth makes a very good timepiece; even today, except for the most precise needs, it is more than adequate. Nevertheless, with the development of atomic clocks we have turned away from the earth definition of the second to the atomic definition. But how do we know that the atomic second is uniform?

One thing we might do to find out is to build several atomic clocks, and check to see if the seconds they generate "side by side" are of equal length. If they are, then we will be pretty certain that we can build clocks that produce uniform intervals of time at the "same" time.

But then how can we be certain that the atomic second itself isn't getting longer or shorter with time? Actually there is no way to tell, if we are simply comparing one atomic clock with another. We must compare the atomic second with some other kind of second. But then if we measure a difference, which second is changing length and which one is not? There would seem to be no way out of this maze. We must take another approach.

TIME: