Apelles hiding behind the painting

Todays post combines two oft-repeated themes here at the Renaissance Mathematicus. We have another highly significant researcher who, however, does not belong to the pantheon of seventeenth century scientific gods and therefore tends to remain unknown to the non-experts. Our subject is also one more refutation of the widely held belief that in the seventeenth century Catholics in general and the Jesuits in particular were anti-science. Today we will take a look at the first man to be involved in a major scientific dispute with Galileo following the invention of the telescope the Jesuit mathematician, astronomer and optical physicist Christoph Scheiner, who was born in the town of Markt Wald in Bavarian Swabia on 25^th July (NS) in either 1573 or 1575.

Christoph Scheinet (artist unknown)

Scheiner attended a Jesuit Latin school in Augsburg from 1591 to 1595 before entering the Jesuit Order in Landsberg am Lech in 1595. He was educated in Landsberg am Lech, Augsburg and Ingolstadt obtaining his doctorate in theology, the normal higher degree for a Jesuit, in Ingolstadt in 1609. Over the years he had held various teaching post in Bavaria and in 1610 he was appointed professor of mathematics in Ingolstadt. The chair for mathematics in Ingolstadt was the oldest in Germany and Scheiner had several illustrious predecessors including Peter Apian. Scheiner is notorious amongst historians of astronomy for his more than somewhat heated dispute with Galileo on the nature of the sunspots and who had the honour of having discovered them first. However this was not his only scientific achievement.

One thing that I personally find fascinating is that Scheiner invented the pantograph in 1603 whilst still a student a fact that illustrates his ingenuity as an instrument maker. Although he first published his invention, which he had however already displayed publically on numerous occasions, in 1631. Now, if I had been writing this in the nineteen sixties or seventies I could be fairly certain that all of my readers would know what a pantograph is, however in this age of computer graphics where the most amazing graphical transformations can be accomplished by the most ham-fisted of us with the simple click of a mouse the pantograph like many other drawing instruments has almost disappeared from public awareness.

Scheiner’s Pantograph

A pantograph is an instrument for copying pictures and diagrams either one to one or scaled up or down. On the apparatus pictured above the three points at the bottom are the operative parts of the instrument. The instrument is anchored with the point on the left (XN) whilst the original drawing is traced out with the other hand with the middle point (MH) steering (OZ). The point on the right (PT) thus draws the required copy. By adjusting the length of the arms one can determine whether the copy is one to one, enlarged or reduced.

The thing for which Scheiner should be most well known, but he isn’t, is his work on the optical function of the eye Oculus hoc est: Fundamentum opticum, which he published in 1609 1619. Although there were many competing theories of vision in antiquity the majority opinion was that the image was formed in the crystal lens at the front of the eye. Even Ibn al-Haytham who laid the foundation of modern optics in the eleventh century CE with his synthesis of ancient Greek optical theory believed that the image was formed in the lens. In 1604 in his Astronomiae Pars Optica Johannes Kepler made a radical change in that he claimed that the lens is just that, a lens, and the image in formed, as in a camera obscura (a name he coined), on the retina at the back of the eye. This is, as we now know, the correct solution. However Kepler’s suggestion did not go down particularly well as any such image would of course be inverted; we would see everything upside down! Kepler’s ingenious and correct solution to this problem was to suggest that the brain copes with this situation telling the viewer which side in up. Now Kepler did not offer any form of empirical evidence for his theories and so they remained more than somewhat disputed; enter Scheiner who delivered the empirical proof that Kepler was right and quite a bit more.

Scheiner took bull’s eyes, the real things and not the middle of archery targets or darts boards. And pared them down so that he could see through the retina from outside of the eye. He then projected an image through the lens and could observe its inverted formation on the retina, Kepler vindicated. Unfortunately for Scheiner in most popular presentations of the history of optics this achievement is almost always wrongly attributed to Descartes. Scheiner’s work on vision contains many other important discoveries on the physiology of the eye making him alongside Kepler, Descartes, Gregory and Huygens to one of the important optical researchers of the seventeenth century.

Scheiner’s Optics

As already stated above Scheiner is most well know for his sunspots dispute with Galileo, which rumbled on for more than twenty years after its initial very heated phase between 1611 and 1613. Scheiner and Galileo both began observing sunspots with a telescope around the same time at the beginning of 1611, although Galileo would later claim he had begun earlier in order to claim priority, whereas unknown to both of them the priority in observation went to Thomas Harriot in England and the priority in publication to Johannes Fabricius in Frisia. The Augsburger businessman and astronomy enthusiast Marcus Welser published two sets of three letters from Scheiner on his sunspot observations under the pseudonym Apelles latenspost tabulam a reference to the fourth century Greek painter Apelles who is said to have displayed his paintings in his shop window whilst hiding behind them to listen to any criticism that might fall from the viewers, hence the title of this post. Scheiner hypothesised that the sunspots were actually small satellites orbiting the sun and casting their shadows on its surface, a theory that preserved the Aristotelian perfection of the heavens. Galileo countered with three letters of his own written in Tuscan and published by the Accademia dei Lincei in which he proved by careful observation and mathematical analysis that the sunspots must be on the surface of the sun, something that Scheiner then came to accept. Welser had declined to publish Galileo’s letters partially because of the gratuitous insults against Scheiner that they contained, some of which even the Lincei removed.

Later in his dispute with another Jesuit Orazio Grassi over the nature of comets, which would eventually lead to the publication of his Il Saggiatore (The Assayer), Galileo even went as far as to falsely accuse Scheiner of plagiarism. Unlike Galileo who basically abandoned his telescopic astronomy in 1613 Scheiner went on to make an extensive telescopic study of the sun, which he published as Rosa Ursina in 1630.

Scheiner Observing the Sun

In the first of the four books of his masterwork Scheiner very carefully detailed the sunspot observations made by Galileo and himself correctly attributing to each his discoveries, something that did not please Galileo at all. Galileo’s supporters rubbished the Rosa Ursina upon publication and the book being a rather turgid scientific study was a flop although it is without doubt one of the most important astronomical works published in the seventeenth century; it just wasn’t very readable!

Scheiner’s Sunspot Observations

In his infamous Dialogo Galileo compounded his sins again gratuitously insulting Scheiner whilst knowingly claiming several of Scheiner’s discoveries as his own. Galileo was not a nice man.

Initially Scheiner had built his own thirty power Dutch telescope and had, like Harriot, observed the sun at dawn through low clouds. Later at the suggestion of his assistant Johann Baptist Cysat, another Jesuit astronomer of some importance, he began to use filters of coloured glass so as not to damage his eyes. Scheiner was the first astronomer to construct and use Keplerian telescopes, two convex lenses, rather than Dutch or Galilean ones, one convex and one concave lens, for his observations, something that Galileo also criticised him for. The Keplerian or astronomical telescope is in fact superior but more susceptible to spherical aberration. It would be another twenty years before other astronomers, largely influenced by Galileo, followed Scheiner’s lead. For his solar observations Scheiner developed his helioscope a Keplerian telescope mounted on a sophisticated stand, which projected the image of the sun on to a screen.

Scheiner’s Helioscope

Scheiner was a first class astronomer and optician who suffered much under the arrogance and spitefulness of Galileo and who deserves to be much better known than he is.