Galileo's Difesa

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On 18 August 2009 I [EFR] received an email from the Head of Special Collections at the University of St Andrews Library asking me to write a short essay on Galileo's Difesa di Galileo Galilei ... contro alle calunnie & imposture di Baldessar Capra for inclusion in a book to be published on the "most interesting and spectacular items" held within the Special Collections. I replied that I would be happy to write such a short essay, but although I knew that the book was extremely rare, I knew nothing of the provenance of the St Andrews copy. In fact it is thought that only a dozen copies of the original publication remain and only three of these have Galileo's autograph - the St Andrews copy being one of these three. Then I was told of its provenance:-
It was bought from a bookseller in Venice by James David Forbes, who was Principal here from 1859 until 1868, and came to us with his Library, which was given to us subsequently. There is a note in Forbes' hand attached to the end board which tells us where he bought it, and gives the interesting information that he authenticated the autograph against original Galileo manuscripts in the Venice archives - and that the dealer didn't realise what he was selling! ... The autograph is a presentation to one of the Contarini family ....
My first thought on seeing that Galileo had presented this copy to one of the Contarini family was that it was probably presented to Giacomo Contarini who was one of the Commissioners of the Venice Arsenal with whom Galileo had exchanged letters in March 1593 about the best place to position oars in a galley. However, on Thursday 20 August 2009 I went to the University Library and inspected the Difesa. It was a thrill to hold such a rare book which had once been held by Galileo and autographed by him. It was immediately obvious, however, that Galileo presented the book to Angelo Contarini, not to Giacomo Contarini as I had expected. Angelo Contarini (1575-1637) was a Venetian ambassador and almost certainly a patron of Galileo. As an aside let us mention that Angelo Contarini was sent to London in 1625 to congratulate Charles I on his accession.
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Here is a transcription of Forbes' note as it appears attached to the cover of the Difesa:-
This "Defence" was written by Galileo himself. This copy is therefore a Presentation Copy to one of the Contarini family, Venetian nobles who were his patrons. The writing is Galileo's autograph as I verified in the Public Library at Venice from Galileo's manuscripts with the aid of the polite librarian which ascertained the point beyond a doubt. I bought the book of Canciani the bookseller at Venice who had not remarked the inscription.

March 1845 JDF
Let me explain that Galileo wrote the Difesa as a strongly worded attack on Baldessar Capra who had plagiarized his writings and was claiming to have invented a mathematical instrument which had been invented by Galileo many years earlier. Galileo uses considerable literary skill in attacking Capra. The fact that 'capra' means goat in Italian is fully exploited by Galileo who does not miss a trick in belittling his opponent. We need now to look at the details of the affair.

Around 1597 Galileo invented the Geometrical Compass. This instrument had, on one side, lines engraved which allowed multiplication, division and extraction of roots. A line also indicated the specific gravities of common metals. The other side of the Geometrical Compass had lines engraved to assist in drawing any polygon on a given line. Galileo wrote an instruction manual which was copied in manuscript for his students' use. For many years this was a perfectly satisfactory situation but eventually Galileo realised that others were considering making copies of his Geometrical Compass. We give more details of this later but, continuing with a chronological account, we next describe a nova seen in 1604.

A nova had appeared in 1572 and had been observed by Tycho Brahe. This had produced much interest and quite some fear at a time when superstition ruled. When another nova appeared in October 1604, interest was high. The star became visible on 9 October and continued to brighten. Galileo first observed the nova on 28 October, just a few days before the star reached its maximum brightness on 1 November. Galileo, at this time Professor at Padua, delivered three lectures on the nova which were so popular that no hall in Padua was large enough to accommodate the audience which came. Of course Galileo could not possibly have had any understanding of what a nova was, but he realised that since it showed no parallax it must be a distant object situated in the realm of the fixed stars. The theory of the universe at that time believed that changes only occurred in the heavens with objects close to the earth. The fact that the nova was a changing object apparently on the sphere of the fixed stars contradicted the then accepted notion. However, Galileo hoped to use the nova to show that the earth was moving. Perhaps, he thought, the change in brightness of the nova is caused by the earth moving relative to the new star. The nova could not be observed towards the end of the year since it was too close to the sun in the sky. When Galileo began to observe it again in the spring he realised that since it was now dimmer his theory that the change in brightness was due to the earth's motion could not be correct.

Around the time that Galileo began observing the nova again in January-February 1605, a treatise was published by Baldessare Capra entitled Consideratione astronomica circa la stella nona dell'anno 1604 . Capra had become a student of Simon Mayr in 1602 and the two had observed the nova in October 1604. Although the treatise appeared under Capra's name, he had been greatly assisted in its writing by Mayr. In the book Capra claimed that he and Mayr had been first to observe the nova (which was probably true) and made fun of Galileo for being so slow to spot it. He also reprimanded Galileo for not acknowledging their prior discovery in the lectures he had given on the nova in Padua. Galileo, who knew Baldessare Capra and his father Aurelio Capra, was very annoyed but worse was to follow relating to the Geometrical Compass.

Galileo had his Geometrical Compass manufactured for sale by the craftsman Marcantonio Mazzoleni whom he retained in his own home. He heard rumours that others were about to manufacture their own version and claim it as their own invention, and he realised that he would lose both money and reputation by having others produce a similar instrument. He decided that a good way of making sure that credit went to him for the invention was to have the handwritten instructions for its use properly printed and distributed. He did so in 1606 publishing the Italian text as Le operazioni del compasso geometrico e militare di Galileo . Sixty copies of the book, dedicated to Cosimo de Medici on 10 July 1606, were printed on a press owned by Galileo; he distributed them among influential people. Galileo deliberately avoided giving any indication of how the compass could be constructed and the instructions only made sense to those who had the instrument. This explains why so few copies the text were produced. Galileo explained in the Preface that he realised that someone was intent on stealing his idea and wanted the press to act as a witness to his priority claim. In many ways this proved to be a mistake for it led not only to the idea of the Geometrical Compass being stolen but also Galileo's instruction manual.

Simon Mayr encouraged Capra to steal Galileo's idea. In early 1607 a Latin version of Galileo's instruction manual entitled Usus et Fabrica Circini Cuiusdam Proportionis appeared under Capra's name. It accompanied an instrument Capra called the Proportional Hoop which he claimed as his own invention and he accused Galileo of stealing his idea. The fact that Galileo's manual had been translated into Latin by Mayr (under Capra's name) was significant, for it clearly meant that they were thinking of selling their version of the instrument on a much wider European scale. Galileo was furious for not only would he lose financially, but he would lose reputation. Perhaps worst of all, he had dedicated Le operazioni del compasso geometrico to Cosimo de Medici, one of his patrons, and if Capra was to be believed then Galileo had committed a crime in dedicating something which was not his to give.

Galileo rapidly took action against Capra. He requested depositions from well-known people who could vouch for his priority. He intended to use these as evidence before a panel set up by the University to judge his complaint against Capra. One of these influential people, Giacomo Alvise Cornaro, replied to Galileo:-
Since I doubt that anybody from this Studio is coming there, I should suggest setting up another congress here, in Padua in the presence of the Signori Rettori of the Town. I spoke to Pilan, who told me that he bought Capra's book, and having carefully examined it, he found that it was copied from Your Lordship, Magini and that German, or Flemish man, and that there is nothing of himself. Therefore, one never says enough about that proud young man's boldness.
"That German, or Flemish man" was Eutel Zugmesser who is mentioned by Galileo in the Difesa as appearing in Padua around 1603 carrying an instrument very similar to Galileo's. Galileo defended himself against the suggestion that he copied from Zugmesser, writing in the Difesa that Zugmesser's instrument was:-
... provided with a few inscribed lines copied from mine, while other lines were omitted and replaced with other ones.
It was at Giacomo Alvise Cornaro's house, with many people present, that Galileo had been able to make them realise that Zugmesser had copied from him. However, after the publication of the Difesa, Zugmesser was offended by what Galileo's wrote about him in the book; in reply he claimed that his instrument was superior to that of Galileo.

Galileo received several replies to his request for depositions which he printed in the Difesa. These include one from Giacomo Alvise Cornaro written on 6 April, one from Pompeo di Pannicchi written on 14 April, and one from Paolo Sarpi, a Venetian scientist and Church reformer, who wrote on 20 April 1607:-
I further affirm that about ten years ago in Padua, Signor Galileo showed me the instrument (described in his book) and explained its uses; and that about two years later, the said Signor made me a present of one, which I still have in my possession.
The University authorities considered the case and rapidly decided in favour of Galileo. Capra demonstrated clearly that he did not understand the mathematics in the book of which he was supposedly the author. The University decreed that all 483 copies of Capra's Usus be given to them to be destroyed and that Capra be expelled from the University. In fact Capra had already sent some copies of his Usus out of the country so not all were destroyed - it is now, like Galileo's Difesa, a very rare book.

Further letters of support were received by Galileo after Capra had been condemned and he also included these in the Difesa. These came from people such as Giacomo Badovere (on 13 May), Marcantonio Mazzoleni, Galileo's technician, (on 24 May), and Giovanni Francesco Sagredo (on 1 June). Sagredo was a Venetian aristocrat and friend of Galileo's who had previously used his influence to help Galileo improve his status. In the Difesa, Galileo also argues against Capra's claim that he had copied Le operazioni del compasso geometrico . He wrote:-
... he [Capra] endlessly claims around Padua that I copied this invention from a book, printed in Germany and in the German language, which he is going to receive and show to everybody.
Galileo did not believe that such a book existed but in fact Capra was referring to one of two books printed in 1604 and 1605 which described a reduction compass attributed to Joost Burgi. However, Burgi's reduction compass is quite different from Galileo's geometrical compass, so Capra's argument does not stand up.

One might reasonably ask why Galileo, having been completely vindicated by the university authorities in his case against Capra, wrote the Difesa. One of his reasons reasons must have been that he knew that Mayr was the actual author and not Capra. However, since everything had appeared under Capra's name he could only proceed against him. The Difesa gave Galileo the opportunity to argue the case that he had not copied from anyone. Galileo wrote in the Assayer (1623):-
Of such usurpers I might name not a few, but I shall pass them over now in silence, as it is customary for first offences to receive less severe punishment than subsequent ones. But I shall not remain silent any longer about a second offender who has tried too audaciously to do to me the very same thing which he did many years ago by appropriating the invention of my geometric compass, despite the fact that I had many years previously shown it and discussed it before a large number of gentlemen and had finally made it public in print. May I be pardoned if, against my nature, my habit, and my present intentions - I show resentment and cry out, perhaps with too much bitterness, about a thing which I have kept to myself these many years. I speak of Simon Mayr of Gunzenhausen; he it was in Padua, where I resided at the time, who set forth in Latin the use of the said compass of mine and, appropriating it to himself, had one of his pupils print this under his name. Forthwith, perhaps to escape punishment, he departed immediately for his native land, leaving his pupil in the lurch as the saying goes; and against the latter, in the absence of Simon Mayr, I was obliged to proceed in the manner which is set forth in the 'Defence' which I then wrote and published.
The Difesa is a fascinating book. Not only does it show some of Galileo's thinking at the time about the structure of the universe, but it also gives great insight into Galileo's character. Another important feature is the feeling it gives for the way in which science was conducted at the beginning of the seventeenth century. It has been a real privilege to hold the book in my hands which was, over 400 years ago, held in Galileo's hands.

Finally let us consider a puzzling feature of the St Andrews copy of the Difesa. There is a stain surrounding Galileo's autograph on the title page. What could be the cause of the stain? One possibility is that someone tried to hide the fact that this was a presentation by Galileo. Although today it seems almost inconceivable that one would want to hide such a fact, it is quite believable that at a time when many lived in fear of the Inquisition, one would want to take care regarding a book presented by Galileo who had been tried and found guilty by the Church. It is in fact generally believed that originally all copies of the Difesa would have been presentation copies autographed by Galileo, and the copies which today have no autograph have had it removed. Now if this is to explain the stain around Galileo's autograph on the St Andrews copy, one still has to try to understand how that could result from an attempt to hide the autograph. Perhaps the most likely cause of a stain is from some adhesive which was used to paste paper over the autograph. One could imagine the adhesive drying out over the long period of time, and the covering paper simply falling off, or that the covering paper has been removed at some stage to expose the autograph. We can, of course, be certain that nothing was covering the autograph at the time Forbes purchased this copy in 1845.

Written by J J O'Connor and E F Robertson
Last Update February 2010