Smoot's Ear

by Robert Tavernor

There are some books that should not be written by certain types of authors. A book on how to seduce a woman should not be written by a priest. A psychopath is the wrong person to write a children’s book. I wouldn’t hold out a lot of hope for a book on theology written by an atheist. And this book should not have been written by Robert Tavernor.

In the first place, Mr. Tavernor is not a good writer. His prose is turgid, dense, and repetitive. In telling the story of the process by which the metric system was developed and adopted in revolutionary France, he bounces backwards and forwards in time. We read of one person’s death; a few pages later, we are told of a report he submitted to a committee. I can accept such sequencing if it is clearly necessary to preserve the continuity of the theme, but Mr. Tavernor doesn’t seem to pursue much of a theme in his paragraphs. My impression is that he simply translated his research notes directly into prose without bothering to organize them.


Nor is Mr. Tavernor’s grasp of the underlying concepts adequate for this book. In medieval times, a huge variety of weights and measures were adopted all over Europe. France had hundreds of different systems for measuring distance, volume, and weight; England was a little better. In both countries, kings had established national standards, but never bothered enforcing them. A simple transaction required careful interrogation by the purchaser: how much iron was he buying? In what kind of pounds? As defined by whom? There was plenty of opportunity for shady sellers to deceive buyers.

Merchants grew increasingly desperate for a uniform system of measures. By 1780, the French king realized the importance of the issue and appointed a commission to look into the problem. And here they ran into the killer problem that bedeviled all measurement systems for more than a century: how could they define a unit of length? If they had a unit of length, it was easy to get to units for area and volume, and a unit of volume filled with water could provide the unit of weight. But what was to be the unit of length?

All units of length in times previous had been based on body measurements. A cubit, for example, was the distance from a man’s fingertips to the base of his elbow. A foot was, well, the length of a foot. But whose arm, and whose foot, should be used? Eventually, people settled on the king’s body as the source of these measurements, but kings change, so they ended up using the measurements of the current king to create an iron rod that was safely tucked away in the treasury. Copies of that iron rod were distributed throughout the kingdom to provide the standard of length. Of course, nobody had to follow the standard, and local lords everywhere substituted their own traditional versions of the various units. Hence chaos.

The search for a scientific standard

The scientists tasked with determining a new standard unit of length wanted something less arbitrary. They knew that they needed something that was objective, and so they rejected the body – anybody’s body – as the standard. They wanted something from the world of science, something permanent. Moreover, it had to be accessible to anybody anywhere on the planet.

There were only two schemes that had any possibility of working. The first was the length of a pendulum with a oscillation time of one second. A second was easily established by declaring that one day – the length of which could be determined by astronomical observations – comprised 86,400 seconds (24 hours times 60 minutes per hour times 60 seconds per minute). Thus, they could use the scientifically precise standard of the earth’s rotation to define a precise length of the time, which could, by use of a pendulum, be made to yield a scientifically precise length.

Except that it wasn’t universal. Scientists already knew that the earth was not a perfect sphere, so that gravity was not the same everywhere, and so a pendulum would oscillate at different rates in different regions. The error was tiny – but did they want a unit of measure that had a built-in error? Add to that the fact that the length of a pendulum changes with temperature, and that air resistance varies with temperature, too, and the pendulum unit of length didn’t seem very precise.

The alternative was the size of the earth, which is neither growing nor shrinking. The problem with this was, how do you measure the size of the earth? It’s not as if you place a ruler on the ground, make a mark, move the ruler to the new mark, make another mark, and so on all the way around the earth. However, it was possible to precisely measure the length of a north-south line on land and then use astronomical observations to determine the latitudes of the end points of the line. If one degree of latitude corresponds to, say, 60 miles, then the earth must be 60 x 360 (21,600) miles in circumference.

But here they ran into the same problem: the earth is not a sphere, it is an oblate spheroid. If they knew the precise shape of the earth, they could still solve the problem, but they didn’t know just how far from a sphere the earth deviated. Hence, the latitude method wouldn’t work, either.

Decision time

What to do? The only two possible methods were each fraught with imprecision. The French committee, after years of hemming and hawing, decided upon the latitude method. They had excellent land survey data covering ten degrees of latitude, and if the British were to carry out a land survey of equal precision, and they combined the two surveys, they could get sixteen degrees of latitude. That would be long enough to produce fairly good results. Moreover, the standard would then be established once and for all. So the French created a new system in which the basic unit of length was called the meter, defined to be one ten-millionth of the distance between the equator and the north pole at the longitude of Paris. This immediately yielded a unit of volume, the liter, defined as the volume of a box one-tenth of a meter on a side. The unit of weight was determined by the weight of one liter of water. Voila!

They also rationalized the system by making it decimal in nature: the various extensions of the units would all be multiples of ten. Thus, a centimeter is one-hundredth of a meter, a millimeter is one-thousandth of a meter, a kilometer is a thousand meters, and so forth. It was a supremely rational approach to the problem. Consider how clumsy the system we use in America is: there are 12 inches in a foot, 3 feet in a yard, and 5280 feet in a mile. What a mess! Then there are ounces, pounds, and tons – but there are two kinds of ounces. And teaspoons, tablespoons, pints, quarts, and gallons. It’s no wonder that the entire world, with the exception of the USA and a couple of tiny countries, has adopted the metric system.

The politics of the transition were complicated. The USA under President Thomas Jefferson serious considered going to metric, but decided against it on the grounds that America’s primary trading partner was Britain, which did not use the metric system. And why did the British reject the metric system? Because they were at war with France! Fifty years later they took up the question again, almost decided to make the change, then chickened out. They didn’t adopt the metric system until 1980.

Back to Tavernor

My problem with Mr. Tavernor’s explanation of all this is his scientific illiteracy. His scientific training is woefully lacking, and his explanation of the process is stained with misunderstandings. Not only does Mr. Tavernor fail to understand the relevant scientific principles; he clearly resents science and scientists. His prose is littered with jabs at both. Mr. Tavernor has an agenda here: he believes that modern systems of measurement are cold and inhuman. They’re not based on the human body like the good old measurement systems of yore. Nowadays the meter is defined as a specified number of wavelengths of a specific emission line of krypton. Mr. Tavernor decries this standard because it is not accessible to the common man; it can only be measured by scientists with specialized equipment. Worse, it’s not art:

“Neither scientists nor historians have considered measure as an art; as a commentary on changing social and political conditions, or as a potent instrument of creativity in the hands of artists, painters, sculptors, and architects, who provide cultures with their tangible imagery and physical legacy.”

Apparently Mr. Tavernor would prefer a measurement system that changes with the times, defined by a cacophony of artists. The book closes with a truly weird chapter on art. I read a few page and gave up. It made no sense and had nothing to teach.

Overall assessment

I do not recommend this book. It does provide an interesting detailed exposition of the historical process by which the metric system came into being, but it makes sense only if you 1) already know the basic story and 2) reassemble Mr. Tavernor’s jumbled tale into something coherent.

By the way, Mr. Tavernor begins his book with a tale of Mr. Smoot, a freshman at MIT whose body was used as a unit of measure to determine the length of a bridge. I cannot recall, however, any point at which Mr. Tavernor writes about Mr. Smoot’s ear. In some ways, then, the title is apropos for this discombobulated book.