PIEZA ELECTRICITY

Wairarapa Times-Age, 14 October 1939, Page 5

PIEZA ELECTRICITY

A NEW TIME MACHINE SCIENTIFIC FIND. HOW QUARTZ CRYSTALS HELP THE ASTRONOMER. In the affairs of the world has arrived a new electric force, so minute that it long escaped attention, but so influential that it has a share in the activities of stars and microbes. It is pieza electricity, the electricity of the squeeze. One of the Curies, before they flew at the higher gime of radium, noted that if a crystal of quartz is squeezed or stretched, it does something more than shudder. Its regular shudderings are accompanied by the release of electric discharges from its faces. Contrariwise, if oscillating electric forces are applied to the crystal it will begin to shudder in response. Shudders, vibrations, oscillations, whether electrical or mechanical are interchangeable because they are the same in number. More than that, they can be counted and the shudders of the crystal will keep in step with the vibrations of the oscillating electric current applied to it. If made to vibrate 100,000 times a second it will go on keeping to its 106,000 vibrations withous pause or change. It is the almost perfect Time Machine. TIMING A STAR. The perfect time machine is what the* astronomers want for timing the passage of a star across the spider line of their transit telescopes. On getting it right exactly, time and time again, depends their knowledge of what the star is doing and how it is travelling through the centuries. Like the small boy who asks the passer-by, they want to know the right time; and few things are harder to come by. The astronomer can go only by his clocks. Since a Dutchman invented the pendulum clock-three centuries ago, about the same time that another Dutchman put together a telescope, and so started modern astronomy, the pendulum clock has held the field for accuracy. Its swing, its oscillation, always takes the same time, while its length is unaltered. In the Science Museum at South Kensington, the pendulum clocks begin with the ancient timepiece of Wells Cathedral, and end with the Shortt Clock made some yiars ago by an English clockmaker of genius, which is the last word in accuracy. THE PENDULUM MAY ERR. What does a pendulum do? It oscillates from side to side, and if it does so every second, we say it has an oscillation of one cycle a second. But however carefully the pendulum is suspended and urged on its way it does not keep to that exact timing, because its length may alter. The wire suspending the bob may stretch, even when made of invar, the most invariable of alloys. The heat of a summer’s day may elongate the wire, or a more subtle influence, some alteration in the pull of gravity, may imperceptibly alter it. Friction may clog the motion. These and other errors will creep in. The invariable right time recedes the more, the pendulum pursues it. In that wondrous Shortt Clock the causes of inaccuracy have been removed as far as seems humanly possible, and the clock keeps time with no more error than one three-hundredth of a second a day. But that does not satisfy the astronomers. At Greenwich Observatory there are seven Shortt clocks, dust proof, temperature proof, immune from all temptation to err, and the average of their times is taken for checking the passing star. That should be good enough, but it is not. The search for the right time goes on like the search for the absolute truth. What can come after the Shortt Clock? The answer is the quartz clock, the clock depending on the recording and the counting of the oscillations' of the quartz crystal. KEEPING ITHE SWING CONSTANT. The ordinary pendulum executes a swing, an oscillation, of one cycle a second. The quartz crystal executes many thousands of cycles a second. So does an alternating electric current, swinging its invisible pendulum also, thousands of cycles a second. The electric current and the oscillating crystal set their pendulums swinging together and keep step with one another. Neither gets out of step, and; neither heat nor friction nor any out-' side influence can alter the crystal's pendulum, because it has none. Its shuddering cycles will always be the same, and because they can be counted they come nearer to keeping the right time than anything that has gone before. There is a quartz clock in in operation which does not change by one five-hundredth of a second a year. It is so accurate that it detected an error in a Shortt clock caused by a variation in the attraction of the moon. The pull of gravity, which is by no means the same all over the world, exerts an influence on pendulums by imperceptible alteration of their length. A clock will not keep the same time at the foot of the Himalayas as at Greenwich. The moon, which pulls up the oceans and raises St Paul’s sometimes six feet a day. will also affect a pendulum. But it cannot alter the beat of the quartz crystal. USE IN BROADCASTING. A quartz cUck is not simple. The -mi crystal’s faces have to tut in a mular way. Its companion electric alternating current demands a battery of cells and other equipment. Evidently it is no clock for the mantelpiece. But there is another employ..lent for the quartz crystal which .■.. mas nearer home. It is being used m wireless broadcasting, and the Postmaster-General has put it in some oi his telephone cables. In the quartz clock the alternating electric current is the supervisor to keep the beats of the crystal in step with it. In the wireless broadcasting ...anon the crystal returns the compliment and secs that the cycles of tne alternating electric discharge remain unchanged. The beats of the transmitter, and of the carrier wave it sends out to the listener’s ear, are regulated by the beats of the crystal. They beat in time and lune. CHANNELS FOR ELECTRIC WAVES. This is highly important when the electric pulses, registered in kilocycles or wavelengths on your wireless set. I rise to a high figure. When sprinters I run the 109 yards they run between strings so as to avoid justling one anether at the high pace which is set. In the ocean in'which wireless waves travcl no strings arc possible, but the waves arc allotted channels. You see them indicated on your wireless set as kilocycles, or the number of beats a second, or in wavelengths.

It is not easy to keep to the channel continuously. The electric runners want more elbow room, the shorter their steps, in order to keep from jostling another runner travelling in a parallel channel. Or suppose, that it is expedient to have two broadcasts working at the same wavelength. How are they to be kept from interfering with one another? The answer is mac you will do best by keeping the "oscillations of the carrier wave strictly io schedule. ONE PART iN A MILLION. Many devices have been tried, but it is the quartz crystal oscillator which best does the trick. It keeps the electric oscillations true for long periods of time with a variation of less than one part in a million. We may almost say that it is beginning to drive the broadcast transmitters. Sir Noel Ashbridge of the 8.8. C., in a recent summary of what it has done, remarks that the Welsh Regional and Penmawr transmitters have used it for a year, and '■’at London Regional, and North and Scottish National are changing over '.o it. We should make it clear that r 'o' l - not narrow the channel of the wireless message to a degree at which vn may expect to have more paths queezed into the highways of broad--asting; but it does keep the waves in ‘he way they should go without interf°rence from their travelling companions. Lastly, the quartz crystal has a span i’ i a'; touches microbes. The crystal when squeezed gives out vibrations which would be sound waves if they "ould bo heard. They are far beyond the human ear, mounting from 20.006 vibrations a second upwards. Some the less rapid vibrations may reach the ears of insects. They certainly stir bacteria: because the length o f —mnv bacteria and viruses is so near ] Pn nth o f the waves. They arc not i h-mr-ficini influence. They kill some bacteria. But also they break up vac'■iims. split molecules, speed up some '’hemical actions —and sterilise milk. They should have a future.