A Measure of Everything: An Illustrated Guide to the Science of Measurement - Softcover

Christopher Joseph studied Metallurgy and the Science of Materials at Trinity College, Oxford and is a member of the Institute of Materials, Minerals and Mining. His published works range from scientific texts to historical articles.

Introduction

Measurement, in one form or another, is one of mankind's oldest and most vital activities. Even before the dawn of civilization, relative measurement-"their tribe is bigger than ours"-was vital to the survival of any individual or group. The members of a hunter-gatherer society needed the concepts of "more," "less" and "enough" (enough time to get home before dark; enough food to ensure that no one will have to go hungry). In fact, when you think about it, the human ability to determine whether the five people gathering berries have gathered enough for the entire tribe is a remarkably sophisticated piece of calculation.

As time passed, and human civilization evolved, such purely relative measurements were no longer always sufficient. With the creation of permanent settlements of ever-increasing size such estimation was, in any case, rather more difficult. The increasing sophistication of language allowed comparisons to become ever more complex -- enough for one person is not always enough for another.

The earliest historical record of a unit of measurement is the Egyptian cubit, in around 3000 B.C.E., decreed to be equal to the length of a forearm and hand (from the back of the elbow to the extended tip of the middle finger) plus the width of Pharaoh's palm. This is, of course, still rather flexible -- my forearm is not the same length as yours, and since neither of us met Pharaoh, we cannot confidently say precisely how wide his palm was. It is not yet much of a step forward from measuring the distance in hand-widths, paces or whatever other approximation springs to mind.

By 2500 B.C.E., the necessary leap forward had been taken. The complicated and rather imprecise definition had been simplified drastically: a cubit was the same length as the prototype cubit, stored safely from harm. This was the "royal master cubit," a black marble rod some 52 cm in length-and the size of the user's forearm was no longer an issue. From this simple model it becomes possible to measure many things; distances, areas, volumes, even masses. (This last was defined relative to the mass of a specified volume of a specified substance- usually water or gold, but many other things have been used.)

With accurate measurement, many things that had been difficult or impossible before were now achievable. Trade (between people, towns or regions) became more sophisticated once it was possible to exchange the precise same quantity of grain for the same quantity of gold (or salt, or fabric, or whatever else was needed) every time.

The most important change brought about by reliable measurement, however, was the possibility of science. Without accurate measurement-and equally accurate recording-no useful form of science, engineering or technology is really possible. Without accurate measurement, you couldn't be holding this book in your hands -- a modern printing press is a huge piece of precision machinery. Dozens or hundreds of carefully designed and accurately made components move a sheet of paper (which must be a particular size) exactly the right distance, at exactly the right speed, for the precisely calculated amounts of ink (in four carefully defined colors) to fit together on the page as text and color diagrams-without disappearing off the edges.

In ancient Egypt, the stars rose and fell in the sky at night, as they had always done. Now, however, they were watched by careful, thoughtful men who measured their movements-the maximum height to which they rose above the horizon, the distance between the points at which they appeared on different nights, and so on. Probably their most important discovery (made by Egyptian astronomers watching the star Sirius) was that the time taken for Earth to orbit the sun was 365 and a quarter days. The Egyptian priesthood, unfortunately, was not impressed. The gods would not have been so foolish, and the priests insisted that the calendar should remain fixed at 365 days exactly. This may have seemed more sensible to them, but it forced their official calendar (with dates precisely calculated for sowing seed, harvesting crops and religious festivals of all kinds) to shift by six hours every year relative to the actual changes of the seasons.

Elsewhere, other civilizations also measured the skies -- without, unfortunately, leaving us the detailed records that the Egyptians kept. Their awe-inspiring creations, of which Stonehenge is perhaps the most famous, leave us with no doubts about their designers' ability to measure -- the sun shines precisely down the main avenue of Stonehenge at the summer solstice. But we have no idea what these immense constructions (as remarkable in their way as the Egyptian pyramids, or the great wall of China) were for.

Six hours in a year seems only a very small inaccuracy, but since the change was always in the same direction it accumulated over time, and, after some 730 years, the Egyptians found themselves celebrating midsummer on the shortest day of the year. The drift continued, through Egypt's long history, with the priests preferring their sacred calendar to the astronomers' detailed and painstaking measurements, until the Romans arrived. Julius Caesar listened to the star-gazers, and added the extra day every four years they recommended to the Roman calendar; his successor Augustus then finally forced the Egyptians to do likewise, bringing their year into line with the rest of the Empire.

The Romans were great engineers, and measurement was important to them in many ways, even if their assumptions were not always correct. Their influence can still be felt today, in an astonishing variety of ways, though the story that the standard gauge of modern railways is derived from the width of a Roman chariot is, alas, a myth. (Most vehicles pulled by two horses are around that width, but the gauge became "standard" because it was the one the best engines were built for in the greatest numbers-the standard width might as easily have been the 3 foot 6 inches still used in parts of Australia, or Brunel's faster and more stable 7-foot width.)

We owe to the Romans many of the names of our traditional units -- and their language has also been plundered for scientific terms. "Ounce" and "inch" both derive from the Roman uncia, meaning a twelfth. Uses of uncia were not limited merely to weight and distance, however. Almost anything could sensibly be divided into 12 parts, and almost anything (at one time or another) was. To a Roman it made perfect sense to talk of unciae of a cake, or an estate-perhaps even a business with owner- ship divided among several people.

For centuries after the fall of Rome, systems of customary units remained largely unchanged; there was, after all, nothing new under the sun to measure. Still, the feudal monarchs of Europe were interested in measurement for the same reason that any government is: if you do not know what a man owns or produces, how can you tax him on it?

As the Renaissance reinvigorated progress in art and science, interest in measurement regained some of its former vigor. Problems, of course, still occurred. Galileo, Copernicus and others suffered imprisonment (or worse) at the hands of the established Church, for revealing the conclusions they drew from their measurements, despite the fact that they were all deeply religious men, who marveled at what they saw as the revelation of the amazing sophistication and complexity of God's creation, and contradicted nothing in the Bible.

Traditional units of measurement continued in use all over Europe, sometimes more different from one town to the next than they were from one century to the next. Steadily, though, they became more accurate and reliable. Candles with hour markings on (where the candle might burn at different rates, or the markings be spaced slightly differently) were replaced by clockwork. While a clock in one town might tell a different time from that in a town 20 miles