Measuring things has become so much a part of daily life that most people take it for granted. And yet the concept of measurement is one of the most sophisticated products of the human mind; without it, there could be no science, no industry, no commerce. this book not only explains the underlying theories of measure, but also describes the history of the tools and techniques involved.

Isaac Asimov begins where mankind did, with the very simplest measurements of length. The human body itself provided most of these–the foot, yard, cubit, and fathom are all based on lengths of various parts of the body. But as society developed, it became necessary to standardize these simple units and to add to them as well. Men needed specific ways to describe volume, temperature, time, speed, pressure, and mass.

And it became more and more necessary to convert measurements from one set of units to another. The story of the metric system, which was designed to simplify this problem, combines fine examples of both human invention and folly. Step by step, Asimov brings the reader up to the highly complex units that must be used in order to measure such phenomena as force, energy, and viscosity, and finally, to a consideration of such forbidding topics as Planck’s Constant and Einstein’s theory of relativity. But by the end of the book, the unsuspecting reader is able to grasp how it is that one can go about putting a yardstick on a hydrogen bomb.

I’m not sure whether this is a book on mensuration or an introduction to an interesting and relatively obscure branch of physics (or if there’s any real difference). The first half of the book is dominated by a slow and careful introduction to some of the basic aspects of how things are measured: the different units used for lengths, what they are derived from, how they are related, how to convert back and forth, and why the metric system is so wonderful. The pace picks up afterwards and the last chapter, in particular, is a breathless look at the units of measurement used in some moderately advanced corners of physics: quantum theory, gravitation, and relativity.

This is, I think, the weakest of the three “realm” books, for a number of reasons.

One problem is the pacing I just mentioned. This leaves even some fairly basic aspects of the subject almost glossed over—measurement of time, for example.

However, I’d say that the book’s biggest problem is that the subject matter is, frankly, rather boring. Asimov certainly makes it as interesting as possible, and it is fascinating in places to see the obscure and hidden reasons why our units of measurement are so dang complicated, but the fact of the matter is that the book is largely a series of multiplications involving hard-to-remember constants (the sorts of things that prompt calculator manufacturers these days to include unit conversions as an automatic feature).

Although there is much in the book which is useful to know, there is perhaps just as much which is not useful to know, and Asimov completely fails to give me any reason why I should, in fact, feel obligated to know how many rods there are in a mile. The result is a book which doesn’t particularly stick with the reader; one finishes it not with a sense of having learned something so much as a sigh of relief that one doesn’t really have to learn something.

(Of course, to his credit, Asimov would agree that there is, in fact, no genuinely useful reason why one should know silly things like that. He once wrote an excellent F&SF essay, “Forget it!,” on that very topic.)

One last criticism. This is a book which has surprisingly not stood up well over time. Particularly in the beginning of the book, Asimov goes to great pains to explain how the official definitions of various units such as the meter have changed over time. Unfortunately, they’ve kept on changing. (The meter, for example, is now defined as the distance light travels in a certain period of time.) Moreover, the use of some of the units or names Asimov describes in the book—“microns,” for example—is now officially discouraged.

This is not, of course, Asimov’s fault, but it does leave the modern reader in an uneasy situation—given the domination of this subject by sheer rote memorization, it becomes difficult to determine how many grains of salt should be used in taking some of the exact numbers Asimov gives: kilometers per mile, the speed of light, and so on. Perhaps the best thing to do is to simply use round figures (a kilometer is 5/8 of a mile, and the speed of light is about 300,000 km/sec) and not worry about the details.