Choosing Sides

shekatkar image

Temple University anthropologist Wayne Zachary was studying a local karate club in the early 1970s when a disagreement arose between the club’s instructor and an administrator, dividing the club’s 34 members into two factions. Thanks to his study of communication flow among the members, Zachary was able to predict correctly, with one exception, which side each member would take in the dispute.

The episode has become a popular example in discussions of community structure in networks, so much so that scientists now award a trophy to the first person to use it at a conference. The original example is known as Zachary’s Karate Club; the trophy winners are the Zachary’s Karate Club Club.

(Wayne W. Zachary, “An Information Flow Model for Conflict and Fission in Small Groups,” Journal of Anthropological Research 33:4 [1977], 452-473.) (Thanks to Snehal Shekatkar for the image.)

Ambiance

https://commons.wikimedia.org/wiki/File:Albert-einstein-house.JPG
Image: Wikimedia Commons

This cottage, at 112 Mercer Street in Princeton, New Jersey, has been home to three Nobel winners: Albert Einstein lived there from 1935 to 1955; physicist Frank Wilczek between 1989 and 2001; and economist Eric Maskin until 2012.

It resides on the National Register of Historic Places and has been designated a U.S. National Historic Landmark, but it bears no outward marker of its significance.

A Look Ahead

In The Art of Computer Programming, Donald Knuth notes an interesting pattern in the common units of liquid measure in 13th-century England:

2 gills = 1 chopin
2 chopins = 1 pint
2 pints = 1 quart
2 quarts = 1 pottle
2 pottles = 1 gallon
2 gallons = 1 peck
2 pecks = 1 demibushel
2 demibushels = 1 bushel or firkin
2 firkins = 1 kilderkin
2 kilderkins = 1 barrel
2 barrels = 1 hogshead
2 hogsheads = 1 pipe
2 pipes = 1 tun

“Quantities of liquid expressed in gallons, pottles, quarts, pints, etc. were essentially written in binary notation,” Knuth writes. “Perhaps the true inventors of binary arithmetic were British wine merchants!”

(Thanks, Colin.)

Sickness and Health

What most clinicians do when they receive a laboratory report is, of course, to look up the normal range for the tests in question. … Traditionally, a normal range is calculated in such a way that it includes 95% of the results found in a group of normal or healthy persons, and, consequently, there is a 5% risk that a healthy person will present with an abnormal laboratory result. Then, imagine that you do ten tests on a normal person. In that case the risk that at least one of these tests is abnormal is (1 – 0.9510) which amounts to 0.40 or 40%. If you do twenty-five tests (and that is not uusual in clinical practice), this chance is 72%! As Edmond A. Murphy puts it so aptly, ‘Therefore, a normal person is anyone who has not been sufficiently investigated.’

— Henrik R. Wulff, Stig Andur Pedersen, and Raben Rosenberg, Philosophy of Medicine: An Introduction, 1990, citing Murphy’s The Logic of Medicine, 1976

A Spider’s World

Spiders are largely blind but experience the world through vibrations in their webs, which they detect with their legs. Now MIT materials scientist Markus Buehler has created a musical impression of that experience. His team made three-dimensional maps of the webs of tropical tent-web spiders, identified the vibrating frequency of each thread, and converted these frequencies into ranges that humans can hear. Threads that are closer to the spider sound louder in the recording.

“The spider web can be viewed as an extension of the body of the spider, in that it lives within it, but also uses it as a sensor,” Buehler told New Scientist. “When you go into the virtual reality world and you dive inside the web, being able to hear what’s going on allows you to understand what you see.”

(Thanks, Colin.)

Viewpoint

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Image: Flickr

Leonardo noted that studies of shadow appeal to the same geometric laws as those of perspective — “in matters perspectival, a light source is no different from the eye [… since] the visual ray is similar to the shadowy ray in terms of speed and converging lines.” Just as perspective considers a scene as regarded from a particular point of view, a shadow is a record of what “the lamp cannot see.”

Philosopher Roberto Casati writes, “This is a strong analogy. There is shadow where the light cannot see. Indeed, shadow is exactly what the light source cannot see. A lamp sees only the things that it illuminates; objects in shadow are behind lighted objects that screen the shadow from the lamp’s perspective. For this same reason, when we examine a shadow, we discover the profile of things from the point of view of the lamp. … Shadow allows us to see a point of view other than our own without even getting up from our seats.”

(From Casati’s Shadows, 2000, via Marko Uršič, Shadows of Being: Four Philosophical Essays, 2019.)

Art and Commerce

Before the 19th century, containers did not come in standard sizes, and students in the 1400s were taught to “gauge” their capacity as part of their standard mathematical education:

There is a barrel, each of its ends being 2 bracci in diameter; the diameter at its bung is 2 1/4 bracci and halfway between bung and end it is 2 2/9 bracci. The barrel is 2 bracci long. What is its cubic measure?

This is like a pair of truncated cones. Square the diameter at the ends: 2 × 2 = 4. Then square the median diameter 2 2/9 × 2 2/9 = 4 76/81. Add them together: 8 76/81. Multiply 2 × 2 2/9 = 4 4/9. Add this to 8 76/81 = 13 31/81. Divide by 3 = 4 112/243 … Now square 2 1/4 = 2 1/4 × 2 1/4 = 5 1/16. Add it to the square of the median diameter: 5 5/16 + 4 76/81 = 10 1/129. Multiply 2 2/9 × 2 1/4 = 5. Add this to the previous sum: 15 1/129. Divide by 3: 5 1/3888. Add it to the first result: 4 112/243 + 5 1/3888 = 9 1792/3888. Multiply this by 11 and then divide by 14 [i.e. multiply by π/4]: the final result is 7 23600/54432. This is the cubic measure of the barrel.

Interestingly, this practice informed the art of the time — this exercise is from a mathematical handbook for merchants by Piero della Francesca, the Renaissance painter. Because many artists had attended the same lay schools as business people, they could invoke the same mathematical training in their work, and visual references that recalled these skills became a way to appeal to an educated audience. “The literate public had these same geometrical skills to look at pictures with,” writes art historian Michael Baxandall. “It was a medium in which they were equipped to make discriminations, and the painters knew this.”

(Michael Baxandall, Painting and Experience in Fifteenth Century Italy, 1988.)

04/10/2021 UPDATE: A reader suggests that there’s a typo in the original reference here. If 9 1792/3888 is changed to 9 1793/3888, the final result is 7 23611/54432, which is exactly the result obtained by integration using the approximation π = 22/7. (Thanks, Mariano.)

A Reindeer Cyclone

Russian photographer Lev Fedoseyev captured this drone footage on March 24 on the Kola Peninsula in the Arctic Circle.

When threatened, a herd of reindeer runs in a circle, making it hard for a predator to target any individual. The fawns are at the center.

False Memory

https://commons.wikimedia.org/wiki/File:Orologio_strage_bologna.jpeg
Image: Wikimedia Commons

On Aug. 2, 1980, a bomb exploded in the main railway station in Bologna, killing 85 people and wounding 200. The blast broke a large clock on the outside wall of the building. It was repaired and continued to run for 16 years, but the image of the clock with its hands fixed at 10:25 became a symbol of the event, and when it stopped working in 1996 its hands were set permanently to that time to commemorate the tragedy.

In 2009 psychologist Stefania de Vito and her colleagues surveyed 180 people who worked at the station or used the trains regularly. Of 173 who knew that the clock is now stopped, 92 percent said that it had always been broken. 79 percent, including all 21 railway employees surveyed, claimed to have seen it set always to 10:25. Of 56 citizens who regularly took part in the official annual commemoration, only 6 remembered correctly that the clock had been working in the past.

“These data indicate that individual memory distortions shared by a large group of people develop into collective false memories,” de Vito writes. In this case, the clock’s symbolic importance “acted as suggestive information and obscured the real experience of seeing the clock working, either as a misleading cue at retrieval or as catalysis for a semantic representation drawn from weak encoding.”

(Stefania de Vito, Roberto Cubelli, and Sergio Della Sala, “Collective Representations Elicit Widespread Individual False Memories,” Cortex 45:5 [2009], 686-687.)