It was the year 1860, scholar and physicist Johann Christian Poggendorff was working as an editor of a well-known magazine when Johann Karl Friedrich Zöllner handed him an illusion. No one knew that Zöllner’s illusion would immediately give birth to the Poggendorf’s illusion.
What Zöllner submitted to him was a piece of fabric that he found peculiar. In his letter to Poggendorf, he described that the parallel lines overlapped by a design of diagonal lines that appeared to move away. Poggendorff intrigued by the illusion, noticed that the fabric depicted another illusion.
He noticed that the fabric did not hold the key to just one illusion, but to a completely new one. He went on to describe the pattern he saw, which resulted from the misalignment of an oblique line.
What is the Poggendorff Illusion?
The Poggendorff illusion consists of three straight lines, black, red, and blue. A grey rectangle conceals the black and red line. Looking at the picture, the blue line looks as if it’s merged with the black line, but this is not the case.
However, if you remove the rectangle, the image clearly shows that the blue line merges with the red line, not the black. This spectacular find garnered much praise associating Poggendorff’s name with the illusion. When people got wind of his discovery, they were quick to investigate this new phenomenon.
What do the Studies Say?
Studies conducted on the Poggendorff illusion stated that viewers see the acute angles bulging, even though the illusion vanishes when the slanted line is vertical or horizontal. If you still do not understand how this illusion works, refer to the spear optical illusion.
In the spear optical illusion, a man is holding two spears in his hands. A black rectangle conceals the spears. When you see the image, you think that the first spear is merging with the spear shown on the right side.
However, clicking the picture reveals that the first spear isn’t merging with the spear on the right side, instead the second spear is the continuation of the spear on the right side. Another way to examine this picture is tracing the spear with your mouse or hand to see which one is merging with the one on the right.
Moreover, his discovery made people revisit a painting that might have used Poggendorf’s illusion to create masterpiece. Peter Paul Ruben’s, The Descent from the Cross, painted in 1611 is a great example of an image that incorporates this illusion. In the painting, the illusion is depicted in the front right ladder with the rail not aligned with the upper rail.
That year the world was exposed to two different illusions and that too simultaneously. Poggendorf’s illusion wouldn’t have been discovered if Zöllner hadn’t given his findings to Poggendorf on that day. These two illusions, amongst others are often incorporated in paintings and drawings, as they give artists a new technique to present their art to their audiences.