Scientists have discovered that there is a missing day in the universe, proving the story in the Bible where the sun stands still. Gang members at the local mall are hiding under cars and slashing women's ankles. Companies are giving away free cash and merchandise if you forward an e-mail message.

These are urban legends, stories that purport to be true but are just made up. They used to be passed along by word of mouth, but now they multiply exponentially on the Internet. Since they often make good sermon illustrations, they are sometimes disseminated at church. E-mail forwarders and especially pastors-who are supposed to be trafficking in truth-working on their sermons can check the veracity of such interesting anecdotes by consulting snopes.com.

But something equivalent to urban legends happens among sober historians, scholars, and theologians. They too can pass along facts that are interesting, that illuminate some issue, that seem to prove some other point, but which have the disadvantage of being untrue. Nevertheless, these stories infiltrate the culture, are taught in classrooms, and become part of the conventional wisdom. Call them "scholarly legends."

For example, it has become a commonplace in discussions of church music that Luther took the tune of a popular drinking song as the melody for "A Mighty Fortress Is Our God." This is used as evidence that musical style does not matter in church music, that secular or even profane forms can convey a biblical message, or, taking it further, that worship "styles" can draw from the popular culture while retaining a strong theological content. That may or may not be true. But the story about Luther is not true.

Richard Lammert, a librarian at Concordia Theological Seminary at Ft. Wayne, Ind., researched the story and posted the results on the seminary's website. Citing a number of musical historians, hymnologists, and Luther scholars, Mr. Lammert provides evidence that Luther almost certainly composed the music as well as the words of the great hymn.

He also shows how the scholarly legend began. Luther composed the song following the medieval and early Renaissance structure known as "bar form." But this refers to musical bars, not drinking bars. That is, measures, as in "twelve-bar blues" or "let's practice those last two bars again," as opposed to the free-flowing Gregorian chant form.

Another scholarly legend is that medieval theologians once held a council to determine how many angels could dance on the head of a pin. Never happened. Mortimer Adler researched the contention and found that it was a lampoon of medieval scholasticism that was not meant to be taken literally: "Those theologians are so picky that they would debate how many angels can dance on the head of a pin." The "would" became a "did," so that, in the scholarly equivalent of the children's game of "telephone" (whispering through a line of people to see how a message can be distorted), it became "medieval theologians did debate" about the dancing angels. Although some of us might think this is actually a very good question, it seems never to have occurred to medieval theologians.

Perhaps the most common of scholarly legends is the view that in the Middle Ages, people believed that the earth was flat, until Columbus proved them wrong. Again, not true, as anyone who reads any medieval literature from Boethius to Dante, or who looks at any medieval art, from cathedral carvings to illuminated manuscripts, could attest. The earth is always portrayed and described as a globe.

That knowledge goes back to the Greeks, who measured the curvature of the earth. True, they thought the earth was the center of the universe and that the planets and stars were a collection of spheres within spheres. This, after all, is what we perceive empirically, the earth standing still while the sun and moon move in a great arc across the sky.

It is true that the scientists of his day discouraged Columbus from his journey-not because they thought he would fall off the edge of the earth but because according to his calculations the earth was much smaller than Greek scientists maintained. As it happened, his scientific critics were right about the size of the earth. Columbus did not land at India, as he thought, but America. Neither side dreamed that another vast land mass lay between Europe and the Indies.

This is related to the scholarly legend that confuses the "Dark Ages"-the period of the barbarian invasions after the fall of the Roman Empire-with the "Middle Ages," or, as the "Enlightenment" thinkers would consider it, any time before their "Age of Reason."