Greeting Card Campaign: 10-22 Fechner Day

Click here to download your Fechner Day card!

Fechner's color wheel

Fechner wheel spinning

It's Fechner Day, a celebration of the contributions of Gustav Theodor Fechner (April 19, 1801 – November 18, 1887).  Try to contain your excitement, especially all you psycho-physicists out there.  This weird little holiday celebrates the German philosopher/physicist/psychologist who founded the esoteric science of psychophysics.  For a taste of what that's about, one of his greatest achievements was demonstrating the non-linear relationship between psychological sensation and the physical intensity of a stimulus via the formula: "S = K Log I".  This tidy little formula is known far and wide as the Weber–Fechner law.  Who Weber was and why he doesn't have his own day is not clear.

However, Fechner did do one fun thing in his life.  In 1838, he discovered the mysterious perceptual illusion we call the Fechner color effect.  You can see the effect when you spin a top with a black and white design on top that was invented by British journalist, amateur scientist and aspiring toy-maker Charles Benham, in 1894 invented A kind of spinning top called Benham's top.  The pattern in figure 2 was printed on top and when it's spun, you can see the Fechner color effect. When you spin the disk, most people see arcs of pale Fechner colors.  These are also called pattern-induced flicker colors (PIFCs).  Not everyone can see them or even see the same colors or even see the same colors at the same time of day or age of life.


Fechner was more of a philosopher than a scientist. He once said, "God, the soul of the universe, must be conceived as having an existence analogous to men. Natural laws are just the modes of the unfolding of God's perfection." He was an indomitably positive sort of fellow who felt the thrill of life in everything.

Fechner taught us that it's possible to find color even in a black and white world. Send your darling spark of color a Fechner Day greeting card to let her know that she brings color to your life.  

Just click on the caption below the picture of Gustav Fechner at the top right.  The link will take you to a pdf file in Google Docs. Remember, instead of printing from Google Docs, click on "File" in the upper left corner, then select "Download" and copy the file to your own computer.  Open it with Adobe PDF Reader or whatever PDF reader you use and print the card from there. For some reason Google Docs doesn't handle fonts well, even though they are supposed to be embedded in the PDF document itself.

This is a side fold card, so when it prints, be sure to tell your printer it's in "landscape" format so you get the whole file. Flip it on the short side to print double-sided. Much quicker that way.

Then go out and find a Benham top and enjoy the Fechner color effect. Or, if the gif file in figure 3 works and you can get it to spin, perhaps you can see the colors yourself.


© 2013 by Tom King