WHAT CORRECT TIME IS AND HOW IT IS OBTAINED.

Taranaki Daily News, 8 January 1918, Page 2

WHAT CORRECT TIME IS AND HOW IT IS OBTAINED.

AN ARTICLE OF EVISRY-DA* INTEREST, Correct time! Ask the average man or woman how he or she gets correct time, and. the invariable reply will be, "Oh, from the .Post Office, or the railway elockfr—the right time, of course—and they get it hy wire from the Observatory." To their mind "correct time" is evideniiy an arbitrary thing, officially fixed and handed out daily by officers of the Observatories of the various State capitals.

The opinion held by the person of average education and, intelligence is that unquestionably the right time is determined from the sun. If a referendum was held throughout X.ew Zealand to-morrow, a vast majority of the people would probably vote the honor of "Time Maker" to the sun.

Here again, great as the majority would be, it would bp wrong. The other day a Press representative had a most interesting chat with Professor Cooke, head of the Sydney Observatory, [who courteously but promptly put the !sun right out of it as the "correct time" maker. He's an adjunct, and a valuable one, but "if we never saw the sun for a whole year," the professor 1 smilingly observed, "'we should still have correct time. Nearly everybody assumes the sun to -be the only time giver, but, as I said, if there was no sun it would noT affect the exact time each day.

"Suppose, for example, you had a fixed post on a racecourse and horses racing roiyid it. As each passed the post it would give you a measure of time. Which simile brings us to the stars; they are fixed objects, and observations taken from them give us the siderial day—a fundamental measure of time, 'but not one that would exactly suit public convenience."

"Well, then, what is the source of absolutely correct time?" the professor was asked. "The revolution of the earth' on. Its axis," came the prompt and emphatic answer. "That's the only clock known to man that doesn't vary a hair's breadth."

"But," suggested the newspaper man, "you can't carry that sort of clock or watch about wit!) von."

"Certainly not, but by the means adopted here you ean get a very good imitation of that exact time, and if you possess a good time-piece voti have every means of checking oven the sligiitest variation."

Then came the startling statement that the revolution of the eartli on its axis does no vary the hundredth part of a second in a thousand years, and even if it did the astronomers would he sure to find it out.

'The sun is not moving uniformly, 50 that if he were followed, and nothing else, you would have noon coming at a variety of times —whic'li wouldn't be convenient to the average citizens. So we astronomers make up an imaginary sun, which we call a 'mean sun.' At any given moment, night or day, you can compute how far away that 'mean sun' is from the fundamental point among the stars, and so can determine the instant at which the 'mean sun' is on our meridan at any given place. That is 'mean noon.' And the first step in converting star time into standard time." "Then the siderial day—that is. the time that it takes the earth to make a complete revolution on its axis—is your fundamental time unit?"

"Exactly," retorts the professor. "True solar time is derived from the sun, but, as I said before, the earth, in its yearly course round the sun, travels with greater velocity in summer than in winter; consequently the true solar day varies in length at different times of the year. Therefore we invent the 'mean sun,' whirih gives us mean solar time. "This brings ua to standard time. There is an infinite number of moridans in New South Wales, and therefore an inconvenient, number of 'mean noons.'' So far public convenience it hn = been decided by Act o( Parliament that we 'shall select one of these meridians, which is a definite multiple of 15 decrees awav from Greenwich. The meridian elected tor New South Wales, Victoria, Queensland and Tasmania is the 150 th meridian, and when the 'mean sun' arrives at the 150 th meridian each day it is standard noon for the States named." So much for the theoretical side of determining standard time—now for the practical part. This, of course, is done by telescope observations in conjunction with siderial and standard time clocks that don't vary more than a fraction of a second in 2+ hours. The average man will tell you with pride that he has a top-hole watch, and clinch* the statement witlh the added information that "it doesn't vary more than a minute, a week." Jf the clocks at the Observatory varied that much in n year the professor and his principal assistant, Mr. W. E. Raymond (one of the best, observers in Australia), would he tearing their hair. The clock which records standard time is kept accurately alternating' currents, so that if it is a hundredth of a second, fast or slow it can lie brought back to exact lime quite easily. This is the flock which, in conjunction with the telescope, give? us (lie exact standard time, which is heralded bv the dropping of the lime ball and tho 'firing of the gun. Tho time ball is dropped automatically. When the hour, the minute, and the second hands all stand at o—tiliat is, simultaneously stand at the exact tick of one O'clock—an electric current is started which releases the ball; so that the first movement is the exact moment at which those who value their watches should check their timekeeping qualities.

1 -Bv an automatic contrivance on the telescope the seconds arc licked off on n tape, and the .slightest variation easily noted. Hence the observer, following the course of stars or sun, niaT?es no mistakes due f'o any slight personal nervousness on his part. Every precaution is taken against error, and those who so gleefully pull out their watches to see if tile gun fires correctly should recollect what producing exact time really means. It is a fascinating topic, which would require column after eollumn to do it full justice; hut it is well that readers should have an idea, however hriellv stated, of all tJhe trouble involved in pro•hieing exact standard time. The question is often asked in Sydney, 'ls the Post, Office clock connected by electric wire with the standard time clock at the Observatory?" It is 'lot, but the Post. Office clock is about as good as you will find anywhere if vou take the first stroke of the hour as vour guide and leave the occasional vaearies of the minute hands alone. Three electric run from the standard clock at the Observatory to .places in Sydney. One goes to n clock-room in the Oeneral Post, Office. If yon as!.- t>" T\c!'ange to put vou on "exact time," you hear the clock ticking out eneli second. When the exact time of the minute

ia reached there 19 a break, Slid the listener can then fix his or her watch op: clock to the second. Another electrical'" connection from the standard clock in the Observatory jroes to the master-clock in the nail of' the Harbor Trust Office, Circular Quay, and a third to a business 'llioii.se in the city. It is well that everybody should know something of exact standard lime and how it is produced Thanks to the courtesy ot Professor Cooke and his first assistant, Mr. W. E. Raymond, this article should do something to that end