Hour Glass 20th CENTURY

Korero (AEWS), Volume 2, Issue 24, 29 January 1945, Page 27

Hour Glass 20th CENTURY

A KORERO Report

<( tf you want to know the time, ask a I policeman,” says the song. But if you want to know the correct time, ask the Dominion Observatory at Kelburn, Wellington. They keep it there, and have kept it for over threequarters of a century. For it was in 1868 that Parliament decided to set up a uniform time service for New Zealand and the Observatory was built and started the job it has never stopped, and is still doing, of acting as official timekeeper to the Dominion. Before the days of radio the time was checked solely by observations of the stars. From this to pure astronomy was a short step, and until five years ago, when the Carter Observatory took over the work, considerable research had been done by the Dominion Observatory in this branch of science. In a plain cool room of this modest brick and stone building, which has incidentally a magnificent view over the city and the whole harbour, stand the clocks : tall clocks, grandfather clocks or, more precisely, pendulum clocks. There is no ornament about them : they have large plain dials, the superimposed seconds dial as big as the top of a circular tobacco tin, and simple wooden cases. But they are remarkably accurate. You or I, if our respective watches kept within one minute of correct time in twenty-four hours, would be satisfied, but not the Observatory. Their idea of accuracy is within a quarter of a second in twenty-four hours. The method by which the accuracy is kept at this high level is elaborate and careful but straightforward. One clock has the job of keeping time. In the pendulum rod is a quantity of mercury to allow for any changes in temperature, though these are not very severe, and

more divergence is caused by changes in barometric pressure or air density. On the other side of the room is a control clock. By adjusting small weights on a platform the size of a ss. piece at the top of the pendulum rod it can be kept to the correct time. It in turn controls a “ slave clock ” by means of an electric circuit. The slave clock is responsible for the time signal which is heard over the air from the broadcasting stations. A simple link up with the seconds dial of the slave clock brings the six teeth on the appropriate part of a wheel successively into contact with a small cam which, through a switchboard, transmits the time signal dots automatically to the radio station, where also they are superimposed on the various programmes as the shrill pips ” we are accustomed to. It is the time signal mechanism which lessens the accuracy of the slave clock and necessitates a control qlock, so exact are the requirements of accuracy here. The Post and Telegraph Department, by the way, prefers a long “ dash ” to a “ pip,” and there is a special clock to fulfil this purpose. This clock also transmits time signals to the seismographs, the instruments which record local and distant earthquakes. Each day the time is checked by wireless from Greenwich and 'Washington. To do this takes less than an hour. If for some reason it were at any time impossible to carry out the check this way, then recourse would be had to a specially mounted 3 in. telescope called a transit instrument standing nearby, and observations taken of the stars. As this takes from two to three hours, however, normally the checks are by wireless.

And if all the clocks stopped ? As they are well cared for, this is unlikely, but what is possible is that a severe earthquake could upset the adjustments of the pendulums. To anticipate such a happening six chronometers in varnished boxes sit on a special table and tick away smugly. Most of them are marine chronometers set in gimbals and no earthquake is likely to upset them. Each clock, slave or control, has a duplicate, so no need for adjustment ever interrupts the maintenance and transmission of the exact time. So by wireless or the stars, by clocks or chronometers, at the Dominion Observatory time marches on—but with exactitude. The Director, incidentally, would agree with the Mad Hatter about timepieces—butter is not good for the works. Underneath the building, in what used to be the storeroom and ammunition dump of a coastal battery situated here towards the end of the last century, is a small cell with a glass window about a foot square in the door. Inside is the Observatory’s most accurate clock. In

order that its accuracy may not be disturbed by fluctuations in temperature, only very rarely is the cell entered. Although founded primarily to provide a uniform time service for the Dominion, and still carrying out that function, nowadays the main task of the Observatory is seismology, the study of earthquakes. The first seismograph was installed in 1916, and four years later the Observatory became the country’s official seismological institute. Since 1932 there have been nearly a dozen stations recording seismic disturbances, with the Dominion Observatory as the central station. In addition, the Observatory acts as a central station for the South-west Pacific area as well as New Zealand. To do this it makes use of data from eastern Australian and island stations in the Pacific, publishing the results in bulletins., which are distributed throughout the world. The simplest seismograph, made in New Zealand by the way, is housed in a small building a few yards from the Observatory. Here a sheet of smoked paper is wrapped round a metal cylinder which slowly revolves and moves also longitudinally driven by a small clock. Three steel pens, their points just touching the paper, are connected to three pendulums, two swinging horizontally on the gate principle, and one vertically. The pendulums are delicately balanced, and the whole is securely bolted to a solid concrete block. Any earth tremor locally will set the pendulum swinging and the pens scratching out their story. When the sheet is finished, it is taken off the roller and varnished. In this way the record is made permanent. This instrument is not sufficiently delicate, however, to measure .earthquakes at a great distance. For more distant earthquakes and the smaller local ones there are three seismographs in the underground chamber. Here in a room lit by two bulbs with special filaments giving a weak red light are the seismographs and their respective recording instruments. Two are long-period seismographs and one a short-period instrument. By period the seismologist

refers to the duration of each oscillation. An earthquake at a great distance has a long period, while the oscillations of a local ’quake will be short and sharp. Each instrument works in a slightly different way, but to describe one will be sufficient. In this instrument, a short-period instrument by the way, a small copper cylinder carrying a small mirror is suspended by tungsten wires. The reflection of a light in the small mirror throws a beam of light on to a cylindrical lens which transforms the beam to a point. The point of light is thrown on to a large cylinder or drum with a sheet of photographic paper (this explains the dim red light) wrapped round it, slowly revolving. At regular minute intervals, controlled by the special signal clock, the beam of light is interrupted. The resultant record when the sheet is developed is for all the world as though some one had been “ doodling ” neatly and regularly slantwise across the paper. And when there is a seismic disturbance it is as though the “ doodler ” had become short-tempered and impatient. That does not end the extent of the Observatory’s work in seismology. Throughout the country, in addition to the regular stations, are scattered recorders, mostly Post Office officials and lighthouse-keepers, who send in to the Observatory reports on any shocks they feel. So that this should be exact and

scientific, a special form is sent to these reporters detailing the various facts the central station wants to know. The intensity of an earthquake is now measured by the Mercalli intensity scale, an improvement on the Rossi-Forrel scale of earlier years. Thus intensity I on the scale is described as “ Not felt except by a very few under especially favourable circumstances,” while at the other end of the scale is XII, “ Damage total. Waves seen on ground surfaces. Lines of sight and levels distorted. Objects thrown upward into the air.” The Observatory has also charted tentatively those areas in New Zealand which are more or less affected by earthquakes. Without wishing to offend local loyalties, it really does look as though the North Cape is a good spot.