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Posts Tagged ‘kilogram

“I used to measure the skies, now I measure the shadows of Earth”*…

From ancient Egyptian cubits to fitness tracker apps, humankind has long been seeking ever more ways to measure the world – and ourselves…

The discipline of measurement developed for millennia… Around 6,000 years ago, the first standardised units were deployed in river valley civilisations such as ancient Egypt, where the cubit was defined by the length of the human arm, from elbow to the tip of the middle finger, and used to measure out the dimensions of the pyramids. In the Middle Ages, the task of regulating measurement to facilitate trade was both privilege and burden for rulers: a means of exercising power over their subjects, but a trigger for unrest if neglected. As the centuries passed, units multiplied, and in 18th-century France there were said to be some 250,000 variant units in use, leading to the revolutionary demand: “One king, one law, one weight and one measure.”

It was this abundance of measures that led to the creation of the metric system by French savants. A unit like the metre – defined originally as one ten-millionth of the distance from the equator to the north pole – was intended not only to simplify metrology, but also to embody political ideals. Its value and authority were derived not from royal bodies, but scientific calculation, and were thus, supposedly, equal and accessible to all. Then as today, units of measurement are designed to create uniformity across time, space and culture; to enable control at a distance and ensure trust between strangers. What has changed since the time of the pyramids is that now they often span the whole globe.

Despite their abundance, international standards like those mandated by NIST and the International Organization for Standardization (ISO) are mostly invisible in our lives. Where measurement does intrude is via bureaucracies of various stripes, particularly in education and the workplace. It’s in school that we are first exposed to the harsh lessons of quantification – where we are sorted by grade and rank and number, and told that these are the measures by which our future success will be gauged…

A fascinating survey of the history of measurement, and a consideration of its consequences: “Made to measure: why we can’t stop quantifying our lives,” from James Vincent (@jjvincent) in @guardian, an excerpt from his new book Beyond Measure: The Hidden History of Measurement.

And for a look at what it takes to perfect one of the most fundamental of those measures, see Jeremy Bernstein‘s “The Kilogram.”

* “I used to measure the skies, now I measure the shadows of Earth. Although my mind was sky-bound, the shadow of my body lies here.” – Epitaph Johannes Kepler composed for himself a few months before he died


As we get out the gauge, we might send thoughtfully-wagered birthday greetings Blaise Pascal; he was born on this date in 1623.  A French mathematician, physicist, theologian, and inventor (e.g.,the first digital calculator, the barometer, the hydraulic press, and the syringe), his commitment to empiricism (“experiments are the true teachers which one must follow in physics”) pitted him against his contemporary René “cogito, ergo sum” Descartes– and was foundational in the acceleration of the scientific/rationalist commitment to measurement…


Happy Juneteenth!

“A measurement is not an absolute thing, but only relates one entity to another”*…




Until now, [the mass of the kilogram] has been defined by the granddaddy of all kilos: a golf ball-sized metal cylinder locked in a vault in France [a replica of which is pictured above]. For more than a century, it has been the one true kilogram upon which all others were based…

Made of a corrosion-resistant alloy of 90 percent platinum and 10 percent iridium , the international prototype kilo has rarely seen the light of day. Yet its role has been crucial, as the foundation for the globally accepted system for measuring mass upon which things like international trade depend.

Three different keys, kept in separate locations, are required to unlock the vault where the Grand K and six official copies — collectively known as ‘‘the heir and the spares’’ — are entombed together under glass bell-jars at the International Bureau of Weights and Measures, in Sevres on the western outskirts of Paris.

Founded by 17 nations in 1875 and known by its French initials, the BIPM is the guardian of the seven main units humanity uses to measure its world : the meter for length, the kilogram for mass, the second for time, the ampere for electric current, the kelvin for temperature, the mole for the amount of a substance and the candela for luminous intensity.

Of the seven, the kilo is the last still based on a physical artifact, the Grand K. The meter, for example, used to be a meter-long metal bar but is now defined as the length that light travels in a vacuum in 1/299,792,458th of a second…

The metal kilo is being replaced by a definition based on Planck’s constant, which is part of one of the most celebrated equations in physics but also devilishly difficult to explain . Suffice to say that the update should, in time, spare nations the need to occasionally send their kilos back to Sevres for calibration against the Grand K. Scientists instead should be able to accurately calculate an exact kilo, without having to measure one precious lump of metal against another…

More of this weighty story at “The kilogram is changing. Weight, what?

* H.T. Pledge, Science since 1500


As we muse on measurement, we might send well-calibrated birthday greetings to August Kundt; he was born on this date in 1839.  An astronomer-turned-physicist, he developed a method to measure the velocity of sound in gases and solids using a closed glass tube (now known as a Kundt’s Tube).

AugustKundt source

We might also spare a thought for another physicist, Niels Bohr; he died on this date in 1962.  A Danish physicist and philosopher, Bohr was the first to apply quantum theory to the problem of atomic and molecular structure, creating the Bohr model of the atom, in which he proposed that energy levels of electrons are discrete, and that the electrons revolve in stable orbits around the atomic nucleus but can jump from one energy level (or orbit) to another– a model the underlying principles of which remain valid.  And he developed the principle of complementarity: that items could be separately analyzed in terms of contradictory properties, e.g., particles behaving as a wave or a stream. His foundational contributions to understanding atomic structure and quantum theory won him the Nobel Prize in Physics in 1922.



Written by (Roughly) Daily

November 18, 2018 at 1:01 am

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