THE METRIC SYSTEM

Evening Post, Volume CXV, Issue 75, 30 March 1933, Page 19

THE METRIC SYSTEM

If you -like, it has nothing whatever to do with radio.. technology; but it is interesting, ncvdrthelcssj that the famous metric system, adopted by mostEuropean countries for practical purposes and by the whole civilised world tor scientific purpose's narrowly missed a perfection. Until.it was invented, weights and -measures were haphazard affairs based on"tfeV length of a kind's arm or the size of a. grain of wheat. Almost every trade had..its own system ot measurement, and" how theI.standard yard and pound ever escaped from the tangle is a puzzle about which whole books have beca written: Tor scientific purposes, some uniform system became essential, and it was in accordance With tho materialistic and practical spirit of science that all the uaits must as tar as possible bo linked together and be based upon some accessible- and invariable reference data. Now every required physical uuit, however remote it may seen to be from such simplicity, can be resolved into terms of length, mass, and time. This is true of all electrical quantities—voltage, current, resistance, capacity, inductance, and so on. Now a unit of length gives quito simply not only a unit of area and of volume (for instance square inch and cubic inch) but of mass, for a cubic inch of some specified material serves at once. In tho metric system tho-chosen, unit, of length, called- the metre, was designed to 'be one tenmillionth part of tho earth's quadrant —the distance.along the earth's surface from the pole ,to the equator—obviously a. reasonably fixecl. rcf erea.ee base This, 'divided into 100 parts, gives the ccutimctro (the scientific unit of length) and ono cubic centimetre oft puro water at 4deg 'centigrade was' adopted as the unit of mass, called tho gramme. Thoro remained the unit of time. Fortunately this already existed as the second—itself a well-known unit ■ easily reproducible in ■ any laboratory. It thereforo .required only, a clqck aud a good survey to establish every required physical measurement unit. (

But while it was in practice easy enough to make a clock that would measure seconds accurately, it was another matter-altogether to measure the earth's quadrant with an unchaljeugable accuracy; in fact, this has never yet been done. It therefore became necessary to establish a standard metre, somewhere about right, and declare it to be the final: reference. The standard metre is about 39.37 inches in length.

Now it so happens that the length of a pendulum; (measured from, the point of-'.suspension to the "centre" of the bob) when-;the pendulum beats seconds, is ,a-. small, fraction of an inch less than the standard .metre. What a pity it is, from tho point of view, of true consistency,, that-tbo founders of the metric, system did not. recognise this, and adopt the length of.'tbe seconds pendulum; as the standard of length. The metric system would then have, had one base instead of two, and a base that could have been definitely determined. - - ' : . '••-. .