The truth obscured

In my previous post I wrote about on this day Internet posting and why I personally do it. At the end of my post I warned of bad factually false postings under this tag and as fate would have it, as I was writing my post I stumbled across just such an example.

The calendar style on this day blog site Today in Science History had for 24 January under their Events rubric the following entry, which is liberally peppered with very avoidable errors:

In 1544, a solar eclipse was viewed at Louvain, which was later depicted in the first published book illustration of the camera obscura in use. Dutch mathematician and astronomer Reinerus Gemma-Frisius viewed a solar eclipse using a hole in one wall of a pavillion [sic] to project the sun’s image upside down onto the opposite wall.


Gemma Frisius’ illustration of a camera obscura used to observe the sun

This first paragraph already contains a number of errors. Gemma Frisius, I’ll come back to the name, was in fact Frisian and not Dutch; In fact The Netherlands as they exist now didn’t exist when he was born and his birthplace, Dokkum, was in the Habsburg Netherlands. He was born Jemme Reinierzoon or Jemma son of Reinier to poor parents in Dokkum in Friesland on 9th Dec 1508. His nom de plume Gemma Frisius is a Latinised onomatopoeic version of his birth name plus the toponym Frisius for Friesland. The Reinerus is a piece of pure invention, one of several, from people who don’t understand his actual name.

The post continues as follows:

He published the first illustration of a camera obscura, depicting his method of observation of the eclipse in De Radio Astronomica et Geometrica (1545). Several astronomers made use of such a device in the early part of the 16th century. Both Johannes Kepler and Christopher Scheiner used a camera obscura to study the activity of sunspots. The technique was known to Aristotle (Problems, ca. 330 BC).

The claim that, “Several astronomers made use of such a device in the early part of the 16th century” is more that somewhat dubious, as apart from Leonard’s descriptions of the camera obscura, which didn’t become known till the eighteenth century, all of the known sixteenth century descriptions of the instrument are post Gemma Frisius, so the later part and not the early part of the century.

The next sentence is simple wrong. Johannes Kepler never studied the activity of sunspots an astronomical sport that he left to others. He did however use a camera obscura of his own design set up in a tent to view solar eclipses in Graz on 30 June 1601 and in Prague on 12 October 1605. Infamously whilst he was busy observing the solar eclipse on the market place in Graz in 1601 a thief stole his purse with thirty silver florins. Whilst still with Kepler, if you are going to talk about the use of the camera obscura in Early Modern astronomy then you really should mention the fact that Kepler coined the name camera obscura.

Christoph (not Christopher) Scheiner did observe sunspot activity; in fact he was the leading observer of such activity in the early seventeenth century publishing his results in his Rosa Ursina sive Sol (1626–1630). However, he didn’t use a camera obscura to do so, he used his machine helioscopica (helioscope) a telescope that he designed to project images of the sun onto a sheet of paper. Interesting in this context is that Scheiner’s helioscope was probably the first ever Keplerian or astronomical telescope, it being irrelevant if the projected image is right way up or inverted.


Christoph Scheiner’s machine helioscopica Source: Wikimedia Commons

Some might object that the method is not substantially different to the use of the camera obscura but although the principle is the same the two instruments are distinct and different and should not be thrown haphazardly together.

I also have problems with the sentence, the technique was known to Aristotle. I would be happier if it read, the phenomenon was known to Aristotle. What he actually wrote in Problems Book XV was the following:

“Why is it that when the sun passes through quadrilaterals, as for instance in wickerwork, it does not produce a figure rectangular in shape but circular?”


 “Why is it that an eclipse of the sun, if one looks at it through a sieve or through leaves, such as a plane-tree or other broadleaved tree, or if one joins the fingers of one hand over the fingers of the other, the rays are crescent-shaped where they reach the earth? Is it for the same reason as that when light shines through a rectangular peep-hole, it appears circular in the form of a cone?”

From these passages it is obvious that Aristotle never actually constructed a camera obscura and although he observed the phenomenon on which it is based he never really understood it.

All of the above might appear to be nit picking to some but a fundamental principle of all historiography is first get facts right and the quoted paragraphs gets almost all of their facts wrong.



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2 responses to “The truth obscured

  1. actually name —> actual name

    projected —-> projection or projected image

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