Category Archives: Metric History

The Americans Who Defined The Meter

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By The Metric Maven

On April 13, 1668 the metric system was born. It had been devised by the English scholar, John Wilkins (1614-1672). The system was elegantly defined. One would take a length of string with a mass attached, and adjust that length until the pendulum had a period of two seconds (one second each direction). Now that you had a standard length you would divide that by ten, and use that length to make a cube, which became the liter. Fill the cube with rain water and the mass is a kilogram.

This system was to be a “Universal Measure” that everyone could use. There was just one perceived problem, the period of a pendulum depends on its latitude, so a seconds pendulum would not be universal. The alternative, measuring a distance on the surface of the earth, was however, a very questionable alternative. James Clerk Maxwell (1831-1879) in his A Treatise on Electricity and Magnetism sums up the situation with the meter in 1873:

In…countries which have adopted the metric system, …[the base unit] is the metre. The metre is theoretically the ten millionth part of the length of a meridian of the earth measured from the pole to the equator; but practically it is the length of a standard preserved in Paris, which was constructed by Borda to correspond, when at the temperature of melting ice, with the value of the preceeding length as measured by Delambre. The metre has not been altered to correspond with new and more accurate measurements of the earth, but the arc of the meridian is estimated in terms of the original meter.

One can sense that Maxwell is satirizing the idea of a measurement unit based on the earth, and exposes the “earth based” meter as being essentially a defined artifact which is not exactly “universal.”

Maxwell had his own viewpoint of how a universal standard of length might be created:

In the present state of science the most universal standard of length which we could assume would be the wavelength in vacuum of a particular kind of light, emitted by some widely diffused substance such as sodium, which has well-defined lines in its spectrum. Such a standard would be independent of any changes in the dimensions of the earth, and should be adopted by those who expect their writings to be more permanent than that body.

Yes, it’s clear. Maxwell is not particularly keen on the current definition of the meter in 1873. Indeed light did seem to be the best option for a standard.

Charles Peirce

This is when the eccentric and abrasive American-born Charles Sanders Peirce (1839-1914) enters the story. Robert P. Crease, author of World In The Balance states:

“He was also one of America’s most important metrologists. He made precision measurements, and improved techniques for making them. His work helped remove American metrology from under the British shadow and put American metrology on its feet.”

Charles was introduced to a spectroscope, which is a device that separates light into its constituent frequencies, by Joseph Winlock of the Harvard Observatory. Spectroscopy was allowing scientists to identify the chemical elements which make up stars. The element helium was first identified as a yellow spectrum line seen during a solar eclipse of the sun in 1868, prior to its identification on earth. I suspect they thought it would probably be a metal given the ium suffix. With the help of his father, Charles became head of the Office of Weights and Measures in 1872. Peirce traveled to Paris in 1876 and brought back brass meter standard number 49, which would be used for the calibration of American standards.

The idea of using light for a standard had been contemplated for some time, but there was a potential problem. Light is a wave, waves travel through a medium (water for water waves, air for sound waves). It was thought that light traveled through a medium, which they called aether. It was believed that the wavelength of light would be altered because of the earth’s rotation in the aether and its solar orbit. This would be like the problem of a seconds pendulum having a different period depending on its latitude. Peirce was aware of this and is quoted by Crease on page 195:

[T]here may be a variation in wave-lengths if the aether of space, through which the solar system is traveling, has different degrees of density. But as yet we are not informed of such variation.

In 1887 the Michelson–Morley experiment failed to detect the aether. This caused a considerable scientific brouhaha, but the aether was not dead yet. It was too powerful of an idea. In the end, after repeated experiments failed to detect the aether, it was decided it must not exist, and light could be relied upon to be a universal standard for the definition of a meter.

One can create light which is produced by a known element by placing its gas inside of an evacuated tube. The tube can then be exited with electricity. We all know that when the gas is neon we call it a neon light, or neon tube. Peirce chose to use sodium for his tube. Peirce attempted to calibrate the distance between the  machined  lines on a diffraction grating, back to his number 49 meter standard using the sodium light. Unfortunately, the lines on the diffraction grating had imperfections that made the lines a bit fuzzy, which limited the resolution. The distance between the lines on the diffraction grating would change with temperature, further decreasing the accuracy. The accuracy of the thermometer he used to monitor the temperature also introduced error. Peirce published his results in 1879. He had tied the meter to a wavelength of light by way of the lines on the diffraction grating. He was the first to do this, but it was still not the method described by Maxwell, which involved counting wavelengths of light.

Illustration of Interferometer from Michelson and Morley’s Scientific American Paper

Albert Michelson read Peirce’s publication and realized that the interferometer he and Morley had developed to detect the ether could be used for the precise measurement of wavelengths which Peirce was pursuing with diffraction gratings. An interferometer splits a single beam of light in two and later recombines it so the two beams are out of phase. This produces a series of light and dark interference patterns. A screw is attached to a mirror that can be used to move the mirror and count the number of light and dark oscillations. Michelson and Morley published this work in 1888. The first sentence of the paper is: “The first actual attempt to make the wave length of sodium light a standard of length was made by Peirce.” The inaccuracies of his method  are described and the advantages of an interferometer are discussed.

They determined that it would take the counting of 400,000 wavelengths to obtain a decimeter (100 mm). Michelson and Morley suggest in their paper:

Probably there would be considerable difficulty in actually counting 400,000 wave lengths, but this can be avoided by first counting the wave lengths and fractions in a length of one millimeter and using this to step off a centimeter. This will give the nearest whole number of wave-lengths, and the fractions may be observed directly. The centimeter is then used in the same way to step off a decimeter, which again determines the nearest whole number, the fraction being observed directly as before.

In 1892 Michelson went to Paris to relate he and Morley’s interferometer work. Unfortunately, Michelson discovered that his sodium light did not produce a single frequency line but was actually a composite of two lines. This caused enough fuzziness to not allow for measurements which were as precise as he needed. Michelson tried both mercury and cadmium and settled on the latter.

In the 1906 book Outlines of The Evolution of Weights and Measures and The Metric System, the authors, William Hallock and Herbert Wade, state (pg 265) that Michelson used “three different kinds of light, viz. the red, green, and blue of the cadmium spectrum, he determined the wave-length of each or the number of times this wave-length was contained in the standard meter. The wave-lengths for each color were as follows:”

Hallock and Wade can hardly control their enthusiasm and excitement at this technical breakthrough:

The accuracy of this work is almost incredible, as the variation in measurements was only about one part in ten million. …..here is an absolute measurement which gives the length of a standard in terms of a natural unit, under conditions reproducible at any time. This, of course, gives a permanent check on the integrity of the meter, as in the event of the international prototype being damaged or destroyed……

It was decided by the participants that pursuing a method of tying the natural phenomenon of light to the meter was to be undertaken. Charles Fabry and Alfred Perot made improvements to Michelson and Morley’s interferometer, and were able to obtain a precision near that of their artifact standard. Improvements to the interferometer continued.

A survey of candidate elements was undertaken to find the best one to use for a new standard for the meter. This uncovered the fact that various isotopes of the elements were emitting light at different wavelengths which caused blurred lines. The search was on for elements that were heavy and had few isotopes. This work continued throughout the 20s and 30s. World War II delayed progress, but in the 1950s enough improvements had been made to schedule a re-definition of the meter in 1960. By international agreement the meter was defined in terms of the wavelength of light emitted by the krypton–86 isotope. The meter was now a length available to all countries without respect to an artifact or geography.

Despite the fact that Peirce, Michelson, and Morley—all American scientists—were instrumental in achieving the dream of a universal meter available to all, America did not convert to the metric system or metric lengths. Even though the lengths used in the US: the inch, foot, yard and mile, are all defined by the meter, America rejects a system of length first defined by an Englishman, and then made universal by Americans. I find great irony that most Americans believe that German Chocolate Cake is of Germanic origin. This is not the case. It was created by Sam German—an American—in the 19th Century. It is almost as ironic as Americans refusing to adopt The French Meter.

If you liked this essay and wish to support the work of The Metric Maven, please visit his Patreon Page and contribute. Also purchase his books about the metric system:

The first book is titled: Our Crumbling Invisible Infrastructure. It is a succinct set of essays  that explain why the absence of the metric system in the US is detrimental to our personal heath and our economy. These essays are separately available for free on my website,  but the book has them all in one place in print. The book may be purchased from Amazon here.


The second book is titled The Dimensions of the Cosmos. It takes the metric prefixes from yotta to Yocto and uses each metric prefix to describe a metric world. The book has a considerable number of color images to compliment the prose. It has been receiving good reviews. I think would be a great reference for US science teachers. It has a considerable number of scientific factoids and anecdotes that I believe would be of considerable educational use. It is available from Amazon here.


The third book is not of direct importance to metric education. It is called Death By A Thousand Cuts, A Secret History of the Metric System in The United States. This monograph explains how we have been unable to legally deal with weights and measures in the United States from George Washington, to our current day. This book is also available on Amazon here.

The “Preferred” Measurement System of the US

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By The Metric Maven

Bulldog Edition

The object to the left is an everyday thing, but it is making a clear statement about the designer’s measurement preference. It may not be apparent what the measurement preference is to you. It might not have been to me had I not read The Design of Everyday Things by Donald A Norman (suggested to me by Sven). The design of even the simplest of objects is done in a manner that provides information on how the designer intends them to be used. A person will unconsciously take an intended design clue, and use an object as intended. Knives are provided with handles, and one doesn’t stop to think which is the best end to hold in one’s hand after early experience and instruction in childhood. Norman cites research which argues there are at least 30,000 everyday things around us, and decreases the number to 20,000 to state: “Suppose each everyday thing takes only one minute to learn; learning 20,000 of them occupies 20,000 minutes —333 hours  about 8 forty hour work weeks.” We have a considerable amount of time invested in learning about our everyday things. When we encounter a can opener, or a scissors, or a potato peeler, we generally know exactly what to expect, how to hold it, and how to use it. One way that a designed object signals how it should be used, is to design it so the ways it may be used are limited, this is called affordance by Norman.

When I worked on the design of televisions, I immediately ran into the idea of affordance. A television motherboard and its chassis were dropped off in my lab, but about seven cables had been disconnected. I protested that it was all apart, and was calmly told by a technician  that all the plugs would only go into one place on the motherboard. Indeed, they did, and I was impressed that because of this affordance, I couldn’t make a mistake.

The affordance of the TV motherboard was essentially foolproof, but often designers can’t restrict a user that much, and the affordance involves only discomfort or a subtle tactile clue. Donald Norman offers this:

Take another example of good design. My felt-tipped marking pen has ribs along only one of its sides; otherwise all sides look identical. Careful examination shows that the tip of the marker is angled and makes the best line if the marker is held with the ribbed side up, a natural result if the forefinger rests upon the ribs. No harm results if I hold the marker another way, but the marker writes less well. The ribs are subtle design cue—functional, yet visibly and aesthetically unobtrusive.

Norman also shows numerous door handles as examples. If we see only a push plate on a door, we have no other choice but to push to open the door. A handle which one can readily grasp cues us that we pull to open it. This brings us back to the measuring cup shown above. Its design is pro-metric, as the metric graduations are facing a person’s eyes when it is held with the right hand. About 70-90% of the worlds population are right handed. Right handed Americans using this measuring cup, would find it uncomfortable and unnatural to place the handle on the left. The measuring cup shown is from the period when the US pretended it might go metric. Measuring cups of this same type, which are currently sold in the US, are all designed so that the imperial graduations face one’s eyes when held with the handle on the right. One of mine is shown below:

Common American Measuring Cup

Measuring cup designs have improved since the 1970s. Some of the ones I now own are “top readable” and only sold (unfortunately) at product parties. Dual scale is always a hindrance to metric adoption, but this set of top reading measuring cups are the best I have encountered.  I have visited many cooking stores and looked online, but have yet to find metric-only measuring cups and measuring spoons. The measuring cup shown below appears to have eliminated a right hand bias as well as being easy to read. Now if I could just purchase a metric-only one.

Top Read Measuring Vessel with Clear Metric Graduations
Left Handed Ruler

The design of common measuring cups is but one example of subtle anti-metric bias in our everyday things. In a previous blog I mentioned that the design of American “metric” rulers hinders their use because of the presence of a centimeter-millimeter dual unit scale, and the rounding of the origin end of one particular metric scale. The origin of the inch scale is placed on the square end, which is much more natural for measuring. For about 10% of our population, which are left-handed, the current dual scale measuring cups are adequately designed for metric use. On the other hand both metric and inch ruler scales  have equally low affordance for left-handed people. Left hand rulers exist which have the numbering from right to left to increase the ease of use by a left handed person.

My father gave me an expandable wrench for my last birthday, which has mm markings on one side, and had inch on the other (yes, I ground off the inch scale). If one holds the wrench as a right handed person would, the inch scale faces your eyes. On the opposite side is the metric scale, which has low affordance for a right-handed person. The wrench is nice because it allows one to immediately see what size a bolt head is in mm, but it is very cumbersome for me to use, as I’m right handed.. I have a better understanding of what left handed people deal with on an everyday basis in our world.

Expandible wrench designed with an affordability preference for inches (click to enlarge)

These examples point to the fact that a preference for imperial measures is designed into our US tools, and US everyday things. But I’ve been assured by non-binding legislation that the US prefers metric measurements. Here is some background:

The Omnibus Trade and Competitiveness Act of 1988 was signed into law by Ronald Reagan. It amended the Metric Conversion Act of 1975, yet didn’t have the word metric in the title of the legislation. President Reagan and Congress apparently were concerned that the voluntary nature of the Metric Conversion Act of 1975 was not clear enough.

Section 3 of the Metric Conversion Act of 1975 is amended to read as follows:

SEC. 3. It is therefore the declared policy of the United States

(1) to designate the metric system of measurement as the preferred system of weights and measures for United States trade and commerce;

(2) to require that each Federal agency, by a date certain and to the extent economically feasible by the end of the fiscal year 1992, use the metric system of measurement in its procurement, grants, and other business-related activities, Except to the extent that such use is impractical or is likely to cause significant inefficiencies or loss of markets to United States firms, such as when foreign competitors are producing competing products in non-metric units;

Well, it has been the case since the 19th Century, that switching to metric is always “impractical” in the US. Apparently there was much concern among our legislators that we have an exception: “such as when foreign competitors are producing competing products in non-metric units;” Apparently Liberia and Myanmar (the last two non-metric holdouts in the world) might flood the US (and the world?) with non-metric products, and thereby destroy what’s left of our uncompetitive non-metric US economy. Thank you President Reagan and Congress for the foresight to see the threat and protect us from the economic danger posed by these two tiny countries, and making an exception. Clearly the 1992 date was meaningless and arbitrary. It made it look like the government was taking action, when in fact it was not. Metric is 21 years past the expiration date for becoming “preferred.”

One can easily see how “preferred” metric is in the US simply by inspecting the design of our everyday things and everyday tools. The legislation is feckless, and crass hypocrisy. It is in line with the strange belief that if we cling onto the trappings of our past, the future may be indefinitely postponed. This emotional response, written in legislation, only postpones the day when reality intervenes, and forces Americans to realize that fantasy is no match for reality. I’m not willing to wait another 150 years hoping America will come to its senses. We need legislation that compels industry to design and make available true metric products, during a short compulsory switchover by industry, government, and education to metric. What we have now is legislation celebrating the the metric system as the preferred system of the future and makes sure it will always remain so.

Related Essay:

The Invisible Metric Embargo

If you liked this essay and wish to support the work of The Metric Maven, please visit his Patreon Page and contribute. Also purchase his books about the metric system:

The first book is titled: Our Crumbling Invisible Infrastructure. It is a succinct set of essays  that explain why the absence of the metric system in the US is detrimental to our personal heath and our economy. These essays are separately available for free on my website,  but the book has them all in one place in print. The book may be purchased from Amazon here.


The second book is titled The Dimensions of the Cosmos. It takes the metric prefixes from yotta to Yocto and uses each metric prefix to describe a metric world. The book has a considerable number of color images to compliment the prose. It has been receiving good reviews. I think would be a great reference for US science teachers. It has a considerable number of scientific factoids and anecdotes that I believe would be of considerable educational use. It is available from Amazon here.


The third book is not of direct importance to metric education. It is called Death By A Thousand Cuts, A Secret History of the Metric System in The United States. This monograph explains how we have been unable to legally deal with weights and measures in the United States from George Washington, to our current day. This book is also available on Amazon here.