The False Suns

The letter in which Descartes recommended Mr. Ferrier to Father Mersenne also contained his response to what this father had told him about the famous phenomenon that had appeared in Rome that year and which had given the philosophers of the time something to do.

On March 20, 5 suns were seen in that city at the same time as 4 parhelia, or false suns, around the sun.

Father Scheiner, a German Jesuit who was then in Rome, had made the observation with some other local mathematicians; and Cardinal Barberini, who was always very zealous for the advancement of the sciences, had sent a description of it to De Peiresc, a counselor in the Parliament of Provence, with a drawing of the phenomenon. Mr. De Peiresc had had several copies made to communicate the matter to all the scholars of his acquaintance and to encourage them to share their thoughts on the phenomenon.

He sent one to Mr. Gassendi who was then in Holland and who had left France with Mr. Luillier, master of accounts, at the end of the previous year for a trip to the Low Countries.

Gassendi, having found in Amsterdam two friends that Descartes had recently made before retiring to Friesland, also wanted to become friends with them, both in consideration of their particular merit and by the desire to have as friends those of Descartes, whom he esteemed infinitely, but whom he had seen only once in his life and whom he did not yet know well enough to maintain a relationship of friendship with him.

The first of these two friends was Mr. De Waessenaer, a gentleman from one of the oldest houses in the province, but who was reduced to practicing medicine.

He had a son who was a skilled mathematician and whom we will have occasion to talk about in more detail later in Mr. Descartes’s life.

The other friend was Mr. Henry Reneri or Renier, who is inappropriately called Mr. Reveri in the letters of Mr. Descartes that Mr. Clerselier had printed, and in the life of Father Mersenne written by Father Hilarion De Coste.

This Reneri, who passed for the first of the followers that Mr. Descartes’s philosophy made in foreign countries, was a native of the small town of Huy or Hoey on the Meuse in the country of Liège.

His father was only a simple merchant and receiver of the chapter of Huy, but his grandfather had been a man of great consideration at the court of Brussels, under Margaret, Princess of Parma, daughter of Charles V, governor of the Low Countries; and he had been chosen to be governor of Prince Alexander, her son.

Our Reneri was 3 years older than Mr. Descartes; he had done his humanities in Liège and his philosophy in Leuven. But having returned to Liège to study theology, he had the misfortune of coming across the institutions of Calvin, the reading of which so changed his mind that he renounced the Catholic religion.

The obstinacy he showed in wanting to remain in his new resolution brought him the disgrace of his relatives, and he could only escape his father’s indignation by fleeing. He retired to Holland and went to Leiden to study the holy scriptures at the French college, where he found people who were willing to contribute to his subsistence. Five years after his flight, his father believed he had to disinherit him after having worked in vain to make him return.

To try to remedy his indigence, Reneri opened a private school in Leiden, where he maintained himself for some time on the pay of his students. His fortune having then put him a little more at ease, he applied himself particularly to philosophy.

This is what gave him access to Mr. Descartes, to whom he made himself known upon his arrival in Holland through the intermediary of Mr. Beeckman, or some other of his old friends from the province.

Gassendi, having found himself in Amsterdam at the beginning of July, had received from Waessenaer and Reneri all the good offices that the first ardors of a recent friendship can suggest to friends. He was so satisfied with their kindness that, out of gratitude, he promised them when leaving Amsterdam for Utrecht on the tenth of July to send one of them without delay the description of the parhelia phenomenon with the account of the observation that had been made in Rome, such as it had been sent to him by Mr. De Peiresc; and to the other a full and reasoned explanation of the parhelia, which he was to compose at his first leisure.

Waessenaer had no sooner received the observation than Mr. Reneri took a copy of it which he sent on the spot to Mr. Descartes. He made the same request to him as to Mr. Gassendi, to induce him to give his thoughts on the phenomenon. But Mr. Descartes, who was busy with something more important, did not appear as diligent as Mr. Gassendi. The latter, seeing himself pressed to keep his word by a letter that Reneri had written to him believing him still in Utrecht, and which he received in Leiden, worked on the spot on his dissertation amidst the movements and difficulties of his trip; and having completed it at The Hague, he sent it to him from the 14th of July.

He added a note of addition containing another observation of four parhelia, or false suns, which had formerly appeared in England on the eighth of April of the year 1223 under the reign of Henry III. This observation was taken from the history of Matthew Paris, and it had been sent to him from Leiden to The Hague by J. Gerard Vossius, who had promised him what he could find in his papers on this subject.

Descartes wanted to make more extensive inquiries before giving his opinion on the phenomenon of Rome, wrote about it to Father Mersenne and asked him in particular for the description he had of this phenomenon, to know if it agreed with the one he had been shown. Father Mersenne, although he had been out of Paris for more than a month for the trip to the Low Countries, did not fail to send it to him by the first opportunity.

Descartes, having compared it with the other, found no other difference, except that Father Mersenne’s indicated that the phenomenon had been seen in Tivoli and Rome, whereas Reneri’s or Gassendi’s indicated that it was in Frescati and Rome; in which it could be that the good Father Mersenne had inadvertently mistaken the word Tusculi, which was in the original sent from Rome by Cardinal Barberini, for the city of Tivoli. This difference was important enough to puzzle Mr. Descartes, who awaited a new clarification on this point from Father Mersenne.

It is to this observation of the parhelia that the public is partly indebted for the beautiful treatise on meteors that Mr. Descartes gave to it a few years later. He interrupted his metaphysical meditations to examine all the meteors in order; and he worked for several days on this subject before finding enough to satisfy himself.

But finally, having put himself in a position by his observations to account for most of the meteors, he wrote about it to Father Mersenne immediately after returning from Franeker to Amsterdam; and he told him that he was resolved to make a small treatise about it that would contain the explanation of the colors of the rainbow, which had given him more trouble than all the rest, and generally of all sublunary phenomena.

He begged him at the same time not to talk about it to anyone, because his plan was to present it to the public as an essay or a sample of his philosophy and to remain hidden behind it like the painter behind his painting, to hear more surely what would be said about it.

“This,” he said to this father, “is one of the most beautiful subjects I could choose, and I will try to explain it in such a way that all those who only understand French can take pleasure in reading it. I would prefer that it be printed in Paris than here; and if it were not a burden to you, I would send it to you when it is done, both to correct it and to put it in the hands of a bookseller.” Mr. Descartes did not hurry to write; but his delay did not make him fail to keep the promise he had made to explain the phenomenon of the four false suns, one of which had a long tail in the manner of comets, and which were accompanied by a large white circle and two irises or rainbows of various colors. He acquitted himself of it in a manner “shorter and cleaner,” but in the public’s judgment more exact, than the Roman and French astronomers who had preceded him. He showed why of these four false suns, the two that were closer to the true sun were colored on their edges, less round and less brilliant than the true sun, from which he proved that they were formed by refraction; and why the two that were farther away were rounder but less brilliant than the other two, and all white without any other color on their edges, which showed that they were caused by reflection.

He explained how the sun that was seen towards the west had a changing and uncertain shape and cast a thick tail of fire from itself that sometimes appeared longer and sometimes shorter. He did not forget the nature of the two crowns that had appeared around the true sun, painted with the same colors as the rainbow; and he showed why the interior one was much more vivid and more apparent than the exterior one; why such do not always appear when several suns are seen; and why the sun is not always exactly the center of these crowns, which can have various centers, although they are one around the other.

This is what gave rise to the tenth or last discourse of his treatise on meteors, where he particularly examined the way in which the clouds that make several suns appear are formed. He claims in this work that an ice ring is formed around these clouds, the surface of which is quite polished; that this ice is usually thicker towards the side of the sun than towards the others; that this is what supports it; and that this is what sometimes makes a large white circle appear in the sky that has no star for its center, as was seen in the phenomenon of Rome. He explains how up to six suns can be seen in this white circle: the first directly; the next two by refraction; and the other three by reflection.

Why those seen by refraction have their edges painted red on one side and blue on the other; and why the other three are only white and have little brilliance.

From which it happens that sometimes only five are seen, sometimes only four, sometimes only three; and why when only three are seen, sometimes only a white bar crossing them appears instead of the white circle. Why, the sun being higher or lower than this white circle, it nevertheless appears at the same height; and why this can make it visible even after it has set and greatly advance or delay the shadow of clocks or dials. He also reports in what case a seventh sun can be seen above or below the preceding six, just as Mr. Gassendi in the life of De Peiresc noted that Father Scheiner had seen a similar number in the same city of Rome in January of the following year. Finally, Mr. Descartes explains in this treatise how three suns can also be seen one on top of the other; and why in that case, one is not accustomed to seeing others next to them, although it is not impossible to sometimes see up to twelve, and even a greater number.