伊斯梅尔·布里阿德Ismaël Bullialdus

伊斯梅尔·布里阿德的母亲是Susanna Motet，父亲是布里阿德；两人都是加尔文主义者。父亲布里阿德的职业是公证人，但也是一位业余天文学家，在卢丹进行观测。他的儿子，即本传记的主人公，这样描述他[6]：-

……一个非常聪明的头脑，以及一种既适合严肃又适合愉快的性格。

苏珊娜和布里阿德老先生于1604年8月3日有了他们的第一个儿子。他随父亲取名为布里阿德，但未能存活。随后他们给次年出生的第二个孩子取名为布里阿德。他活了下来，并成为著名的天文学家和数学家。他就是本传记的布里阿德。

让我们注意到，在Loudun有一个重要的知识分子圈子，布里阿德 Senior是其中一员。他们在当地一家旅馆聚会，并为其他来访学者提供了一个聚集点。这对年轻的布里阿德很重要，他参加了这些聚会，并结识了当时许多重要人物。当然，随着这个小男孩长大，父亲教他天文学，尽管他学习的是法律和人文学科，而不是科学。我们知道，布里阿德的父亲观测了1607年的彗星，这颗彗星后来被称为爱德蒙·哈雷彗星。他还在1618年观测了另一颗彗星，当时他的儿子13岁。这对父子来说一定是一件激动人心的事，而布里阿德后来在他1645年的著名论著中发表了他父亲对这些彗星的观测细节。

布里阿德由两位加尔文主义父母抚养成为加尔文主义者。然而，当他21岁时，他皈依了罗马天主教。到26岁时，他被任命为天主教神父，一年后，即1632年，他去了巴黎。在那里，他担任图书管理员，与Pierre和Jacques Dupuy兄弟有关联，他们正在为皇家图书馆工作。这座图书馆的历史可追溯到14世纪，于1567年至1593年间迁至巴黎。它于1622年编目，也就是布里阿德到达巴黎的十年前，而Pierre和Jacques Dupuy走遍法国，为图书馆收集书籍和手稿。de Thou家族也深度参与皇家图书馆，他们为布里阿德的图书管理员工作提供了经济支持。布里阿德具备他所从事工作所需的技能，因为他是一位广博的学者，对历史、哲学和古典学有浓厚兴趣，同时又在巴黎的科学圈中游刃有余，在那里，他凭借父亲传授的天文学坚实基础开始崭露头角。

作为图书管理员，布里阿德广泛游历意大利、荷兰和德国购买书籍。1657年，在他的两位雇主Dupuy兄弟去世后，他担任法国驻荷兰大使的秘书，这位大使是de Thou家族的成员。他再次从事图书管理员工作，这次是为同一位法国大使de Thou，但在1666年与他发生争执后，他住在Laon学院。他生命的最后五年从事与职业生涯开始时相同的职业，成为圣维克多修道院的神父。

布里阿德是布莱兹·帕斯卡、马兰·梅森和皮埃尔·伽桑狄的朋友，并支持伽利略和尼古拉·哥白尼。他出版了De natura lucis Ⓣ（光的本性）（1638），该书主要基于他与皮埃尔·伽桑狄关于光的本性的讨论。他当然不同意皮埃尔·伽桑狄的原子论，而是采取了自己关于光的三维观点。他的下一部著作Philolaus Ⓣ（克罗顿的菲洛劳斯）（1639）实际上在出版前已以手稿形式存在多年。它支持尼古拉·哥白尼的世界观，其唯一引人注目之处在于，对于一个新近皈依天主教的人来说，公开支持这样的观点必定相当困难。他的下一部著作是关于数学的，即他编辑的士麦那的塞翁的算术文本Expositio rerum mathematicarum ad legendum Platonem utilium Ⓣ（柏拉图数学著作阐释），这是该文本的第一个印刷版本。它于1644年问世，同年晚些时候，他于12月16日写信给马兰·梅森（当时在罗马）[6]：-

我想很少有人见过我的忒翁，因为只有少数几本被带到意大利。荷兰人和波兰人收到了几本。

1645年，布里阿德出版了Astronomia philolaica Ⓣ（菲洛劳斯的天文学），其中接受了行星的椭圆轨道。他在给马兰·梅森的同一封信中写道：-

《菲洛劳斯的天文学》终于完成了，但我手头有一场争执，因为Jean-Baptiste Morin——按照他自己的观点——整个天文学的王子，遇到了某些对他不利或不合他意的东西。我向他提出的简单建议应该使他更明智，并在对从未说过如此残酷言论、也从未冒犯过他的人作出伤害性陈述时更加克制。

他声称，如果存在一种行星运动力，那么它应当与距离的平方成反比（约翰内斯·开普勒曾主张一次方）：-

至于太阳抓住或握住行星的力，由于它是物质性的，其作用方式如同手一样，它沿直线发射到整个世界的范围，并且像太阳的种相一样，随太阳的物体一起转动；现在，既然它是物质性的，在更远的距离或间隔处它就会变得更弱、更稀薄，其强度减小的比例与光的情形相同，即距离的二重比例，但成反比，也就是$\large\frac{1}{d^{2}\normalsize}$。

然而他随后论证说，太阳并不产生行星运动力：-

……我说，太阳受其自身的形式驱动绕其轴旋转，正是通过这种形式它被点燃并发出光，确实我说，没有任何一种运动压迫其余的行星……确实[我说]各个行星是由赋予它们的各个形式驱动着旋转的……

Astronomia philolaica代表了约翰内斯·开普勒与艾萨克·牛顿之间最重要的论著，它在艾萨克·牛顿的Principia中受到赞扬，特别是因为其中的平方反比假设及其精确的表格。布里阿德的哲学有一个方面很值得评论——即他相信简单的解释，而且他希望许多不同的观测性质都源自单一的原因。他没有实现自己的目标，那将由艾萨克·牛顿实现，但至少他为这样的发展奠定了基础。他后来出版了更多的数学著作，但它们没有多大意义。De lineis spiralibus（1657）与阿基米德和帕普斯的工作有关。然后在1682年他出版了Opus novum ad arithmeticam infinitorumⓉ（关于无穷算术的新著作），他声称这部著作澄清了约翰·沃利斯的Arithmetica infinitorumⓉ（无穷算术）。另一部值得提及的天文学著作是Ad astronomos monita duoⓉ（给天文学家的两个警告）（1667），在其中他首次确定了变星米拉·塞提的周期，这是一颗长周期变星。他给出333天，这是一个很好的估计，只长了大约一天。

布里阿德是克里斯蒂安·惠更斯的亲密伙伴，克里斯蒂安·惠更斯在发现土星环时首先求助于他，并送给他摆钟。然而，对布里阿德进行现代研究最有趣的方面之一是，他是一位多产的通信者。这些通信涵盖了大约六十年，从1632年他到达巴黎后不久到他去世前一年。同样有趣的是，这些通信涵盖了马兰·梅森去世后的45年，所以我们可以认为他填补了马兰·梅森的角色。我们在这里谈论多少封信？令人惊讶的是，历史学家有超过5000封信，因此他们的评估仍然是一项持续的任务。这些信件充满了关于科学和政治的消息，其中许多本质上是琐碎的。

尽管他活跃在与马兰·梅森相关的圈子里，该圈子后来成为科学院，但他从未被选入该机构。然而，他于1667年被选为皇家学会的外国通讯院士。

Ismael Boulliau's mother was Susanna Motet and his father was Ismael Boulliau; both were Calvinists. Ismael Boulliau, the father, was a notary by profession but was an amateur astronomer who made observations in Loudun. His son, the subject of this biography, described him as having [6]:-

... a very clever mind and a character suited both to seriousness and pleasantness.

Susanna and Ismael Senior had their first son on 3 August 1604. He was called Ismael after his father but he did not live. They then called their second child, who was born in the following year, Ismael. He did survive and become a famous astronomer and mathematician. He is the Ismael Boulliau of this biography.

Let us note that there was in Loudun an important circle of intellectuals of which Ismael Boulliau Senior was part. They met in a local hotel and provided a focus for other visiting scholars. It was important for the young Ismael who attended these meetings and became acquainted with many leading men of the day. Certainly as the young boy grew up he was taught about astronomy by his father although he studied law and the humanities rather than science. We know that Boulliau's father observed the comet of 1607 which would later be called Halley's comet. He also observed another comet in 1618 when his son was 13 years old. This must have been an exciting event for both father and son, and Boulliau later published details of his father's observations of these comets in his famous treatise of 1645.

Boulliau was brought up a Calvanist by two Calvanist parents. However when he was 21 years old he became a convert to Roman Catholicism. By the age of 26 he was ordained as a Catholic priest and one year later, in 1632, he went to Paris. There he worked as a librarian associated with the brothers Pierre and Jacques Dupuy who were working on the Bibliothèque du Roi. This library, which dated back to the fourteenth century, was moved to Paris between 1567 and 1593. It had been catalogued in 1622, ten years before Boulliau arrived in Paris, and Pierre and Jacques Dupuy travelled throughout France amassing books and manusctripts for the library. The de Thou family were also heavily involved with the Bibliothèque du Roi, and they provided financial support for Boulliau in his work as a librarian. Boulliau had the right skills for the work he undertook, for he was a broad scholar with a deep interest in history, philosophy and classics, yet equally at home in the scientific circles of Paris where he began to shine building on the firm foundations in astronomy taught by his father.

In his capacity as librarian Boulliau travelled widely in Italy, Holland and Germany buying books. In 1657, after the death of his two employers the brothers Dupuy, he worked as a secretary to the French ambassador to Holland who was a member of the de Thou family. He was to work again as a librarian, this time for the same French ambassador de Thou, but after a dispute with him in 1666 he lived at the Collège de Laon. He spent the last five years of his life in the same occupation in which he started his career, becoming a priest at the Abbey St Victor.

Boulliau was a friend of Pascal, Mersenne and Gassendi and supported Galileo and Copernicus. He published De natura lucis Ⓣ (1638) which was based largely on the discussions he had been having with Gassendi on the nature of light. He certainly did not agree with Gassendi's atomic theory but took his own three dimensional view of light. His next work Philolaus Ⓣ (1639) had in fact been available in manuscript form for some years before it was published. It supported the world view of Copernicus, and is only remarkable in that it must have been quite difficult for a recent convert to Catholicism to openly support such views. His next work was on mathematics, namely his edition of the arithmetic text Expositio rerum mathematicarum ad legendum Platonem utilium Ⓣ by Theon of Smyrna which was the first printed version of this text. It appeared in 1644 and later in the same year he wrote to Mersenne (who was in Rome) on 16 December [6]:-

I think few people have seen my Theon, as only a few copies were taken to Italy. The Dutch and Polish received several.

In 1645 Boulliau published Astronomia philolaica Ⓣ which accepts elliptical orbits for planets. He wrote in the same letter to Mersenne:-

The Astronomia philolaica is finally complete, but I have a quarrel on my hands, as Jean-Baptiste Morin, the Prince - according to his own views - of the whole of Astronomy, has come across something not to his advantage or liking. The simple suggestion I put to him should make him wiser and more reserved in making injurious statements against someone who has never made such cruel remarks, and who has never offended him.

He claimed that if a planetary moving force existed then it should vary inversely as the square of the distance (Kepler had claimed the first power):-

As for the power by which the Sun seizes or holds the planets, and which, being corporeal, functions in the manner of hands, it is emitted in straight lines throughout the whole extent of the world, and like the species of the Sun, it turns with the body of the Sun; now, seeing that it is corporeal, it becomes weaker and attenuated at a greater distance or interval, and the ratio of its decrease in strength is the same as in the case of light, namely, the duplicate proportion, but inversely, of the distances that is, $\large\frac{1}{d^{2}\normalsize}$.

However he then argues that the sun does not produce a planetary moving force:-

... I say that the Sun is moved by its own form around its axis, by which form it was ignited and made light, indeed I say that no kind of motion presses upon the remaining planets ... indeed [I say] that the individual planets are driven round by individual forms with which they were provided ...

The Astronomia philolaica represents the most significant treatise between Kepler and Newton and it was praised by Newton in his Principia, particularly for the inverse square hypothesis and its accurate tables. There is one aspect of Boulliau's philosophy which is well worth commenting on - namely the fact that he believed in simple explanations and moreover he wanted many different observed properties to result from a single cause. He did not achieve his aim, that would be achieved by Newton, but at least he set the scene for such developments. He later published further mathematics texts, but they are not of much significance. De lineis spiralibus (1657) related to work by Archimedes and Pappus. Then in 1682 he published Opus novum ad arithmeticam infinitorum Ⓣ which he claimed clarified the Arithmetica infinitorum Ⓣ of Wallis. The other astronomy text worth mentioning is Ad astronomos monita duo Ⓣ (1667) in which he established for the first time the period of the variable star Mira Ceti, a long-period variable. He gave 333 days which is a good estimate and only about one day too long.

Boulliau was a close associate of Huygens who turned to him first with his discovery of the rings of Saturn and sent him pendulum clocks. One of the most interesting aspects for modern research into Boulliau, however, is that he was a prolific correspondent. This correspondence covers about sixty years, between shortly after his arrival in Paris in 1632 and the year before his death. It is also interesting that this correspondence covers 45 years after Mersenne's death, so we can think of him as filling his role. How many letters are we talking about here? It is amazing to realise that historians have over 5,000 letters and so their assessment is still an ongoing task. They are full of news, much of it trivial in nature, about science and politics.

Although he moved in the circles associated with Mersenne which later became the Academy of Sciences, he was never elected to that body. However, he was elected a foreign associate of the Royal Society in 1667.