Metric measures
Oliver Stewart
Metrication is not going to be shifted. Although weights and measures legislation and the objections of some industries and professions may interfere with the rate at which it settles in, the family of modern metric units has taken possession and the British public are going to be obliged to live with it.
Yet the public have never been properly introduced to modern metric units. For they are not the same as the units of the original metric system which everybody learnt about at school. Nor are they even the same as the metric units of sixteen years ago. They are the units of the Systeme International d'Unites or SI which was established in 1960 by the General Conference of Weights and Measures which is the world authority on measuring units.
The differences between the metric system and the SI involve definitions, nomenclature and coherency. The old metric system had material standards, the platinum-iridium metre bar, for instance, whereas the SI has two of its most important standards expressed in atomic radiations; the optical metre and the caesium second. Material standards are readily understood by most laymen whereas atomic standards are not understood except by those who have had some education in atomic physics.
We have here the first of the reasons for public resistance to giving up British imperial measures—all of them based on material standards—and going over to SI measures. A metal bar tells anyone who looks at it roughly what length it represents. But the fundamental radiation of the krypton-86 isotope, which is used for defining the SI metre, has little to say to the ordinary man about length.
Similarly the unit of time of the early metric system is simple and straightforward. It is obtained by dividing up the time of a tropical year. But the unit of time of the SI has nothing to do with vulgar things like months and seasons and years. It is obtained by counting cycles of radiation of a caesium resonance clock. So the SI second is now a second of atomic time, whereas the earlier metric second and, indeed, the second we think about when we are concerned with matters of everyday life, is a second of astronomical time. The two scales are not the same and the metrological scientists have had to go to absurd lengths to relate them. For example they have had to juggle with radio time signals, putting a bit on here and taking a bit off there.
Again, then, public approval of the SI is obstructed by its atomic and largely incomprehensible characteristics. It simply cannot come within striking distance of the ordinary measurer; the carpenter, the navigator, the surveyor.
The SI's nomenclature is touchingly historical. But that means that it is less informative than the earlier nomenclature. Pressure, for instance, could be expressed in kilogramme force to the square centimetre and that conveyed some indication of meaning. But the SI unit of force is the newton (N) and the SI unit of pressure is the pascal (Pa) in commemoration of two famous men. Similarly the SI unit of power is the watt (W) and not the horsepower. Another British scientist is commemorated in the SI unit of energy, the joule (J).
These are rather ingenious names for units and they will gradually receive acceptance. But it is no good thinking that they facilitate the general use of the SI. They tend to militate against it. It will be a boon when all power from that of cars to that of ships and trains and everything else is given in watts, for the term horsepower has been much abused and degraded and now has no precise meaning. Similarly it will be a boon when the joule is used for all energy references. But the larger public does not seem to have been made aware of these advantages of the SI.
The Metrication Board has worked hard; but it does seem to have tended to take a too superficial view of what people want to know. Housewives are of course concerned about buying potatoes in kilogrammes instead of pounds; but they are also concerned with the basis of measuring, with the government arrangements for standardising units used in the shops. They are as interested as anyone else to know about the SI unit of mass and to understand why, if the SI has no unit of 'weight', the critical measure should not be the newton. The Metrication Board has tended to underestimate their interest. And this failure to enable the larger public to get to close quarters with the SI is almost certainly the thing that is making the change to the SI more difficult and more troublesome.
The SI has many good and many bad qualities. It needs a complete overhaul before the larger public is let loose on it. But time is short if the EEC directive is to be met. And the first and most important practical move towards metrication is a spread of knowledge and information about the system of measuring to which we are committed, that is to say about the International System of Units. Without the spread of such knowledge and information we in this country will founder in a confusion of false ideas and unfounded impressions.
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