亚历克西·布瓦尔Alexis Bouvard

亚历克西·布瓦尔出身贫寒，事实上他出生在日内瓦湖以南阿尔卑斯地区的一间小屋里。可以想象，这给了他一个艰难的开端，很难想象在这样的起点下，他如何最终成为一位享有世界声誉的受尊敬学者。获得教育的机会很少，所以他小时候几乎没有受过教育，在山上长大，学会了牧羊童的技能。然而在1785年，18岁时，他去巴黎生活并接受数学课程，以便通过计算员工作谋生。如今我们认为计算机是一种机器，但当时计算员是进行数值计算的人。尽管他几乎没有钱支付教育费用，法兰西学院确实提供免费课程，布瓦尔在那里学习。在参观巴黎天文台后，他对天文学着迷。他还意识到这是一个他的计算技能特别有用的领域。他于1793年作为学生天文学家进入天文台，并于1795年被任命为天文学家。

1794年，布瓦尔遇到了皮埃尔·西蒙·拉普拉斯，当时后者正在撰写他的伟大杰作Mécanique célesteⓉ（天体力学）。皮埃尔·西蒙·拉普拉斯认识到布瓦尔的计算技能，很快让他进行其理论所需的复杂计算。意识到布瓦尔的潜力，皮埃尔·西蒙·拉普拉斯安排他在1794年获得经度局的重要职位。布瓦尔在那里工作了他的整个职业生涯，赢得了细心观察者和能干数学家的声誉。在他工作的许多年里，他为Annuaire（相当于Nautical Almanac的法国版本）提供表格。他工作的一个完全不同的方面是注释考辛翻译的伊斯兰数学家伊本·优努斯的著作，后者以其天文观测和众多三角学及天文学表格而闻名。

作为观测者，布瓦尔的技能体现在他发现了八颗彗星，而他作为计算者的技能则体现在他对这些彗星轨道的计算上。他观测到的前四颗彗星分别出现于1797年、1798年、1801年和1805年。在计算了一颗于1818年可见的彗星的轨道后，他意识到这与他1805年观测到（并计算了轨道）的是同一颗彗星。这颗彗星现在被称为约翰·弗朗茨·恩克彗星。他基于自己进行的4000多次观测而从事的月球理论研究是一项非凡的成就，并为他赢得了法国研究院1800年颁发的一项奖。他还获得了其他重要荣誉，表明国际学界对他的高度尊重，例如他于1803年当选为科学院成员，并于1826年当选为伦敦皇家学会会士。

他最重大的贡献之一是预言了天王星轨道之外的一颗行星。这一过程的第一步是他在1808年出版了Tables astronomiqueⓉ（天文表）——木星和土星轨道的表。当他出版这部著作时，天王星自1801年被发现以来仅被研究了七年。他希望在他计划于1821年出版的Tables新版中纳入天王星的表。到那时，已经找到了天王星被发现之前九十年间其位置的十一项记录（当然当时并未意识到所观测到的是一颗行星）。由于天王星有84年的周期，布瓦尔试图找到更多发现前的记录以改进其轨道的计算。其中三项发现前的记录来自Pierre Lemonnier，因此布瓦尔翻阅了他旧观测的15个对开页，试图找到更多观测记录。他又找到了1736年至1780年间的九项观测记录，使发现前的记录总数达到20项。他还可以利用两套出色的发现后观测序列，一套来自巴黎天文台，另一套来自格林尼治天文台。

利用手头的全部数据，布瓦尔建立了一个包含77个方程的方程组，但无法从中找到该行星可能的轨道。起初他假定发现前的数据存在误差，并且尽管他为获得这些发现前数据付出了种种努力，他还是只用发现后的数据来计算他的Tables。然而这并未解决问题，因为几年后观测到该行星远离了其预测位置。布瓦尔认为这是由于另一颗行星扰动了天王星的轨道，但尽管他请巴黎天文台的一位天文学家跟进这一想法，却毫无结果，因为对布瓦尔来说不幸的是，那位天文学家在他提出请求后不久就离开了。布瓦尔本人在能够跟进这一想法之前就去世了，但他的想法构成了约翰·柯西·亚当斯和于尔班·勒维耶工作的基础。他们在1846年对一颗扰动行星（后来命名为海王星）位置的预测，导致其在布瓦尔去世三年后被发现。海王星被发现后，人们意识到海王星在1821年之前加速了天王星的运动，此后则使其减速。事实上，如果这两颗行星在各自轨道上的位置与实际情况显著不同，天文学家可能需要长得多的时间才能意识到天王星正受到另一颗行星的扰动。

Alexander 以如下文字结束了他的传记[1]：-

布瓦尔才华横溢却为人谦逊，是一位不知疲倦的计算者，直到临终前夕仍在进行计算。完全可以说，他停止计算之时，便是他生命终结之日。

澳大利亚的布瓦尔是由法国水手在发现西澳大利亚时以他的名字命名的。

Alexis Bouvard came from a poor background, in fact he was born in a hut in the Alpine region south of Lake Geneva. As one might imagine this gave him a difficult start and it is hard to imagine how he managed to end up a respected scholar with a world-wide reputation given this beginning. There were few chances to obtain schooling so he had little education as a boy, growing up to learn the skills of being a shepherd boy in the hills. However in 1785, when aged 18, he went to live in Paris and received mathematics lessons so that he could earn his living as a computer. These days we think of a computer as a machine but at this time a computer was a person who carried out numerical calculations. Although he had little in the way of money to pay for an education, the Collège de France did offer free courses and Bouvard studied there. He became fascinated by astronomy after a visit to the Paris Observatory. He also realised that this was an area where his calculating skills could be particularly useful. He entered the Observatory as a student astronomer in 1793 and in 1795 was appointed as an astronomer.

In 1794 Bouvard met Laplace who was at that time working on his great masterpiece Mécanique céleste Ⓣ. Laplace recognised Bouvard's computing skills and soon had him carrying out the complex calculations required for his theory. Realising Bouvard's potential, Laplace arranged for him to be offered a position in the important Bureau de longitudes in 1794. Bouvard worked there for the rest of his career earning a reputation as a careful observer as well as an able mathematician. He supplied tables for the Annuaire (the French equivalent to the Nautical Almanac) over the many years he worked there. A completely different aspect of his work was annotating Caussin's translation of the work of the Islamic mathematician Ibn Yunus, known for his astronomical observations and for his many trigonometrical and astronomical tables.

As an observer Bouvard's skill is marked by the fact that he discovered eight comets, and his skill as a calculator is seen from his computation of their orbits. The first four comets he observed appeared in 1797, 1798, 1801 and 1805. After computing the orbit of one which was visible in 1818, he realised it was the same comet as he had observed (and computed its orbit) in 1805. This comet is now known as comet Encke. His work on lunar theory based on over 4000 observations he had made, was a remarkable achievement and earned him a prize from the Institut de France in 1800. He received other significant honours indicating the high esteem in which he was held by the international community, for example he was elected to the Academy of Sciences in 1803 and elected a fellow of the Royal Society of London in 1826.

One of his most significant contributions was his prediction of a planet beyond the orbit of Uranus. His first step in this process was his publication in 1808 of Tables astronomique Ⓣ - tables for the orbits of Jupiter and Saturn. When he published this work Uranus had only been studied for seven years from the time of its discovery in 1801. He wanted to include tables for Uranus in a new edition of the Tables he planned for 1821. By this time eleven records of the position of Uranus during ninety years before its discovery (of course without realising that the observation was of a planet) had been found. Since Uranus had an 84-year period, Bouvard attempted to find further pre-discovery records to improve the calculation of its orbit. Three of the pre-discovery records were due to Pierre Lemonnier, so Bouvard went through 15 folios of his old observations in an attempt to find further sightings. He found nine more records of sightings made between 1736 and 1780 giving him a total of 20 pre-discovery records. He also had at his disposal two fine series of post-discovery observations, one by the Paris observatory, the other by the Greenwich observatory.

Using all the data at his disposal, Bouvard produced a system of 77 equations but was unable to find a possible orbit for the planet from them. At first he assumed that there were errors in the pre-discovery data and, despite all the efforts he had made to obtain this pre-discovery data, he only used post-discovery data to compute his Tables. However this did not turn out to solve the problem since after a few years the planet was observed to be far from its predicted position. Bouvard believed this was due to another planet perturbing the orbit of Uranus but, although he asked an astronomer at the Paris Observatory to follow up the idea, nothing came of it since unfortunately for Bouvard the astronomer left soon after he made his request. Bouvard himself died before he could follow it up but his ideas formed the foundation of the work by Adams and Le Verrier. Their predicted position of a perturbing planet (later named Neptune) in 1846 led to its discovery three years after Bouvard's death. After its discovery it was realised that Neptune had accelerated the motion of Uranus up to 1821, then had retarded it after that. In fact if the positions of these two planets in their orbits had been markedly different from what it happened to be, it may have taken much longer for astronomers to realise that Uranus was being perturbed by another planet.

Alexander ends his biography [1] as follows:-

Brilliant but modest, Bouvard was an indefatigable calculator, and engaged in computation until the eve of his death. It could well be said of him that he ceased calculating only when he ceased living.

Cape Bouvard in Australia was named after him by French sailors when they discovered Western Australia.