If you’re driving on the highway and pass a car traveling in the opposite direction, the frequency of its engine noise seems to drop. In 1980, Liverpool Polytechnic mathematician J.M.H. Peters realized that this pitch drop might be used to estimate the speed of the passing vehicle. Pleasingly, he discovered that each semitone in the interval corresponds to 21 miles per hour (to within 2 percent). If the other car’s engine seems to descend a whole tone in pitch as it passes you, then it’s traveling at approximately 43 mph; if it drops a minor third then it’s traveling at 64 mph; and so on.

“The reader should practise by humming a given note pianissimo increasing gradually to fortissimo at which point the hum is lowered by a chosen interval, … diminishing again to pianissimo, this being meant to imitate the effect of being suddenly passed on a quiet country lane by a fast moving high powered motor vehicle.”

(J.M.H. Peters, “64.8 Estimating the Speed of a Passing Vehicle,” Mathematical Gazette 64:428 [June 1980], 122-124.)

Every positive integer can be represented uniquely as the sum of one or more distinct Fibonacci numbers in such a way that the sum does not include any two consecutive Fibonacci numbers.

Above, 51 = 34 + 13 + 3 + 1.

Discovered in 1952 by Dutch mathematician Gerrit Lekkerkerker (and remarked 20 years later by Edouard Zeckendorf).

If nature be regarded as the teacher and we poor human beings as her pupils, the human race presents a very curious picture. We all sit together at a lecture and possess the necessary principles for understanding it, yet we always pay more attention to the chatter of our fellow students than to the lecturer’s discourse. Or, if our neighbor copies something down, we sneak it from him, stealing what he himself may have heard imperfectly, and add to it our own errors of spelling and opinion.

— G.C. Lichtenberg, quoted in W.H. Auden’s A Certain World, 1970

This is beautifully well done — a humiliating list of all the ways your brain can deceive you (click to enlarge).

Designed by John Manoogian III.

Another geometric magic square from Lee Sallows:

(Thanks, Lee!)

This is a picture of a cow. If you can’t see it (I couldn’t), there’s an explanatory image on page 66 of John McCrone’s 1991 book The Ape That Spoke.

The experience illustrates how the brain is able to construct a picture from limited data by relying on patterns and experience.

Steaming from New York to the Azores in 1867, Mark Twain noted a curious companion overhead:

We had the phenomenon of a full moon located just in the same spot in the heavens at the same hour every night. The reason of this singular conduct on the part of the moon did not occur to us at first, but it did afterward when we reflected that we were gaining about twenty minutes every day because we were going east so fast — we gained just about enough every day to keep along with the moon. It was becoming an old moon to the friends we had left behind us, but to us Joshuas it stood still in the same place and remained always the same.

(From The Innocents Abroad.)

02/11/2025 Reader Catalin Voinescu writes:

Mark Twain is talking absolute nonsense here.

The moon is in (almost) the same phase as seen from all over the world. It rises and sets at roughly the same local time, regardless of longitude, and the relation between phase and time of day when the moon is visible is the same everywhere (the full moon peaks at midnight; a week later, the last-quarter moon rises around midnight, peaks in the morning and sets around noon; and so on).

Even ignoring moon phase and local time, the moon rises, peaks and sets almost 50 minutes later every day, so gaining 20 minutes every day would not be enough.

(Thanks, Catalin.)