On Friday a white sedan with “County of Morris
Weights and Measures” painted on the doors was parked outside the supermarket
where I most commonly shop. An inspector was likely inside the store checking
the scales. There is also a statewide agency and a national one. Inspectors
from various levels of government in all parts of the world have been performing
much the same job for thousands of years. I’ve seen the car in the parking lot
before, but it caught my attention more than usual this time because of an item
in the news about weight – or, more accurately, mass. This past week the world
got a new kilogram. Regrettably, it isn’t different in value from the old one,
so if you have a metric bathroom scale (which I recommend just because the
number in kilograms is so much lower than the number in pounds) you don’t get
to recalibrate it. The value remains the same but it is calculated differently.
Standard weights and measures existed in Sumerian
times. They were a necessity for trade then as they are now. There had to be
some way of expressing how much of this one would trade for how much of that,
and of course taxes (originally in goods – usually grain) had to be calculated
somehow. Sumerian inspectors, like those of Morris County today, existed to
counter the perennial temptation of traders to tinker with scales. Even after
the invention of coinage in the sixth century BCE, the coins commonly were
weighed when delivered because of the illegal but common practice of shaving gold
and silver coins in hopes of passing them off at full face value while keeping
the shavings. Larceny has never been far from the human heart. Inevitably there
were discrepancies from port to port when measuring weights, lengths, and even
time, since all standards were local. These problems continued into the 18th
century when the need for better standards grew more important not only for
trade and industry but for scientific inquiry. Perhaps the most lasting benefit
to have come from the French Revolution is the metric system adopted in 1795.
The U.S. made the metric system official (yes, it really did) in the Metric Act
of 1866; the English system is not official and never has been even though
Americans cling stubbornly to it in everyday use, but for regulatory purposes
its units are defined by metric conversion factors.
The metric system from the start was intended to be based
on natural properties: the gram, for example, originally was the weight of 1
cubic centimeter of water and the meter was 1/10,000,000th of the
distance from the equator to the North Pole. Physical conditions can affect
these measurements, however, so they were swapped out for physical objects by
the end of the 19th century. The meter became a platinum-iridium bar
and the kilogram until this past Monday was a cylinder of 90% platinum and 10%
iridium sitting in a case in Sèvres. These, too, presented problems. The length
and mass of these objects are not constant but change slightly due to
contamination and oxidation, so in the latter half of the 20th
century an effort was made to define metric units in terms of constants. In
1960 the meter was redefined as the distance light in a vacuum travels in
1/299,792,458 second. But what is a second? It is not enough to say it is 1/86,400th
of a day, because the length of a day varies as earth’s rotation rate varies
with changing sea levels. In 1967 a second was redefined as the
time that elapses during 9,192,631,770 cycles of the radiation produced by the
transition between two levels of the cesium 133 atom, even though this means International
Atomic Time drifts slowly from Universal Time (the common clock based on the
earth’s rotation). The kilogram for a long time resisted efforts at
redefinition since various proposed redefinitions proved to be ultimately
circular. On Monday, however, the kilogram finally got a non-circular
redefinition in terms of the Planck constant. We also got new definitions of
the kelvin, ampere, and mole in terms of natural constants.
Happy Retirement |
It’s often said
that the important things in life can’t be measured, such as the value of
freedom, affection, kindness, and contentment – or for that matter hate,
meanness, and anguish. This might not be entirely true. One frequently can
determine a cash value of something like stress or some aspect of freedom by
seeing how much money a person will demand to suffer the former or surrender
the latter. There may well be an exact number. However, there is little doubt
that such measurements are subjective: your dollar figure will be different
from mine, whereas your kilogram is exactly the same as mine. The new
definitions don’t much impinge on my daily routine. I won’t be buying a cesium
atomic clock to tell time; I’ll continue to rely on my $11 watch even though I
need to adjust the hands a little every couple of months. Nor will I be
calculating my mass from scratch in terms of the Planck constant; I’ll step on my
bathroom scale, which is probably off by 1% or so. Nonetheless, it’s nice to
know those things in principle can be done. In a largely subjective and all too
often polarized world, it is reassuring that some things, at least, are
objective.
Lord of The Lost – The Measure of
All Things