Prentice Hall promotes a silly story as fact

Editor's Introduction -- Prentice Hall Earth Science (a middle-school textbook) teaches students that nobody was sure about the shape of our planet until Christopher Columbus's voyage in 1492 gave "final proof" that Earth "was indeed round." The students are learning rubbish. Both the shape and the approximate size of Earth had been known to the ancient Greeks, and this knowledge had been preserved and elaborated over the centuries. Columbus, like other educated Europeans of his day, was able to use factual information about Earth's shape and size in making useful geographic calculations.

The notion that 15th-century Europeans believed Earth to be flat is derived from a story that was invented in the 1800s and was retold and embellished, with signal results, in a book of fictionalized "history" published by the American novelist Washington Irving. Irving fabricated a scene in which Columbus, suspecting that Earth was spherical, was assailed by ignorant priests who thought that Earth was flat -- and Irving's scene was so compelling that it was widely accepted as fact. The flat-Earth story quickly became a popular piece of pseudohistorical folklore, and it remains popular today among people who have had little education. These evidently include the people who produce "science" books for Prentice Hall.

This article was published in The Textbook Letter
for January-February 1992, accompanying reviews
of Prentice Hall Earth Science.

Fake "History" That Is Flatly Wrong

Lawrence S. Lerner

The writers of Prentice Hall Earth Science say, on page 213:

For thousands of years, most people thought that the earth was flat. But as early as 300 B.C., the ancient Greeks theorized that the earth was round. Yet they still drew maps of a flat earth.

As people explored more of the world, they were able to map large areas of it. In 150 A.D., the famous Greek astronomer Ptolemy made maps that included Europe, Africa, and most of Asia. Even more important, these maps showed the earth as round!

For hundreds of years after Ptolemy's work, mapping was neglected. Much knowledge of the world, as well as the idea of a round earth, was forgotten. In the fourteenth century, interest in Ptolemy's work was renewed. Once again, people believed that the earth might be round. Columbus's voyage to the New World was final proof that it was indeed round.

That multi-layered congeries of nonsense does as much harm by omitting truth as by teaching falsity. Why has Prentice Hall put that fake "history" into a schoolbook?

The sphericity of Earth was known to the Greeks long before 300 B.C., and it appeared in the writings of Aristotle (384-322 B.C.), who was summarizing old knowledge. Indeed, Eratosthenes's excellent and famous measurement of Earth's circumference dates from 250 B.C. or so, long before Ptolemy's time.

Prentice Hall's "history" is not only imaginary but silly. Just why would the ancient Greeks, if they "theorized" that Earth was spherical, persist in drawing maps of an Earth that was flat? For that matter, just how does one tell that a map is showing a flat Earth, not a spherical one? And on what was the Greeks' theorizing based? Why have Prentice Hall's writers failed to cite any of the observations from which the Greeks were able (just as we are) to infer Earth's shape? For example:

  • One can see farther from a masthead or a tower than from ground-level.

  • During a lunar eclipse, the shadow that Earth casts on the Moon always has the shape of the shadow that one sphere casts on another.

  • The length of the shadow cast by a vertical post, at noon, depends on latitude. (This was the basis for Eratosthenes's work.)

Prentice Hall's notions about Columbus are pure fantasy. How did Columbus's trip show that Earth "was indeed round"? One might say that Magellan's expedition (1519-1522) showed something like that, because the expedition eventually regained its home port by sailing ever westward. Columbus, however, did no such thing. Moreover, Prentice Hall's writers are unaware of the historic and scientific setting in which Columbus worked. Knowledge of Earth's shape had not been "forgotten," and it is wrong to say that Columbus and his contemporaries merely "believed" that Earth "might be" spherical. They knew Earth to be spherical, and Columbus himself carried out (and fudged) calculations that reflected this fact. Consider:

Columbus's plan for reaching Asia involved sailing westward at a latitude approximating the Tropic of Cancer (23.5 degrees North), to exploit the northeast trade winds. According to information that had been gained over many centuries, the eastward distance to the Asian coast, at that latitude, was about 8,000 miles; and according to Eratosthenes's findings, the total distance around the world at that latitude was about 23,000 miles. So Columbus's westward voyage would have to cover 15,000 miles (i.e., 23,000 minus 8,000), which was far beyond the range of the ships of the time. This could hardly inspire confidence in the people from whom Columbus would seek political and financial support.

Fortunately for him, however, Eratosthenes's measurement had been repeated by others. Most of the results were close to the one that Eratosthenes had obtained, but a few were substantially larger or smaller. Columbus seized upon the smallest plausible figure, some 17,000 miles; he also assumed that he would find outlying islands long before he got to the Asian coast itself. Now he reasonably could tell prospective supporters that he would have to travel only 5,000 miles (a distance that conceivably could be covered by existing ships) before reaching some kind of land.

In fact, of course, Columbus found land -- not in Asia but in the New World -- after sailing only 3,000 miles. Along the way, he kept a bogus log in which he deliberately understated each day's progress, so that his fearful crew would not know how far they were from home. Even so, the crew came close to mutiny.

Instead of telling this rich history, with all the scientific insights it affords, Prentice Hall's writers provide ignorant fakery. Why?

Lawrence S. Lerner is a professor in the Department of Physics and Astronomy at California State University, Long Beach. He served on the panel that wrote the 1990 framework for science education in California's public schools, and he is a director of The Textbook League.


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