莱昂·傅科Léon Foucault

莱昂·傅科的父亲，傅科 傅科 Fortuné 傅科，是一位出版商，通过出版一套关于法国历史的优秀文集而赢得了相当好的声誉。当傅科年幼时，他的父亲因健康状况相当差而退休，全家从巴黎搬到南特。然而退休并没有改善他父亲的健康，他于1829年在南特去世，当时傅科九岁。他的母亲决定他们返回巴黎，从十岁起，傅科与母亲住在旺吉拉尔街和阿萨斯街交汇处一栋相当精美的房子里。这栋房子今天仍然存在，并标有一块纪念牌。

不仅傅科的父亲身体不好，傅科本人也是一个非常虚弱的孩子。他一只眼睛近视，另一只远视。这使他外貌显得相当笨拙，而傅科对自己的外貌变得敏感，倾向于独处，使情况更糟。他的母亲确实给了他良好的教育机会，送他去了斯坦尼斯拉斯学院，但他似乎没有充分利用这些机会。他的老师形容他懒惰，不按时交作业，因此他的母亲不得不请家庭教师在家教育他。朱尔·安托瓦内·利萨茹比傅科小大约两岁半，是他童年为数不多的朋友之一。他写道：

关于这个男孩，没有什么预示他将来会声名显赫；他身体娇弱，性格温和、胆怯且不外向。他体质虚弱，做事缓慢，使他无法在学院学习。多亏了母亲监督下尽心尽力的家庭教师，他才得以成功学习。

然而，傅科确实与斯坦尼斯拉斯学院的一名学生阿尔芒·斐索成了好朋友。

如果说学校的学业不合傅科的喜好，他却开始展现出其他才能。十几岁时，他喜欢制作玩具和机器，其中一些确实非常精巧，比如蒸汽机和电报机。他的灵巧使母亲认为他会成为一名出色的外科医生，因此，在获得高中文凭后，他于1839年进入巴黎的医学院。起初他进步顺利，他的教授阿尔弗雷德·多内对他的进步非常满意。然而，在他第一次医院实习期间，他看到血就晕倒了。在试图克服这个问题之后，他意识到自己永远无法履行医疗职责，便退出了。然而，多内希望他继续以不接触病人的方式将自己的才能用于医学科学事业，于是雇用他做自己的助手。

就在开始担任多内的助手之前，傅科参加了达盖尔关于其摄影方法的讲座。傅科的朋友斐索曾与他同去，两人一起实验，改进摄影工艺。傅科将他新的摄影技能与为多内所做的工作结合起来，设计出一种通过显微镜拍摄照片的方法。为此，他必须发明一种强大的电光源来照亮被拍摄的物体。1845年，傅科和多内出版了A course of microscopy，其中包含80张显微镜下物体的照片。

多内是Journal des Débats的科学编辑，该报每日出版。他于1845年从这一职位退休，将任务交给了傅科。约瑟·伯特兰在[2]中写到了傅科以非凡成功完成的这项任务：

25岁时，既未在学校也未从书本学到什么，对科学充满热情但对学习并不热衷，傅科承担了让公众理解科学家的工作并对科学界领军人物的著作价值做出评判的任务。从一开始，他就表现出极大的敏锐，基于比预期更多审慎的良好判断力。他的最初几篇文章很出色；它们富有灵性。他认真对待自己的职责。在毫无经验的情况下，投身于最高层次的科学及其所有混乱与问题之中，他确保了自己在一个平庸即意味着失败的角色中取得完全的成功。

……总是彬彬有礼，却又追求真理，傅科运用深思熟虑的判断。此前默默无闻，这位既无科学出版物也无已知科学发现的年轻人，展现出一种沉静的权威和坦率，令许多顶尖科学家感到不快。

弗朗索瓦·阿拉戈是在傅科与Donné合著的书出版时得知他擅长显微镜摄影的。1845年，他找到自己私下认识的傅科和斐索，问他们能否尝试拍摄太阳的照片。他们成功了，并拍摄了有史以来第一张太阳照片。照片清晰地显示出若干太阳黑子。弗朗索瓦·阿拉戈非常高兴，并看到了傅科为科学院进行其他实验的潜力。他接着建议傅科和斐索尝试测量光在水中的速度。这是弗朗索瓦·阿拉戈本人想要进行的实验，但他日益衰退的视力意味着他无法亲自从事要求严苛的实验工作。在使用弗朗索瓦·阿拉戈的方法开始工作后不久，傅科和斐索发生了争执。结果他们分道扬镳，各自尝试独立完成实验。

傅科现在设计了自己的方法来处理测量问题，建造了一台蒸汽机来驱动旋转镜。1850年4月，他证明光在水中比在空气中传播得慢。这与光的波动理论所预言的一致，但与微粒理论所预言的相矛盾。傅科写道[2]：

我没有发明旋转镜，也没有发明消色差透镜，也没有发明网格，也没有发明测微计，但我有幸能够将这些由其他科学家设计的仪器组合起来，从而解决了一个十二年前提出的问题。

傅科的下一个想法是，如果他能够设计出一种摆的支架，使摆能够在任何方向上自由运动而不受任何阻力，那么一旦让它运动起来，它就会在空间中保持其摆动平面，而地球在其下方旋转。1851年1月，他在自己房子的地下室里成功建造了这样一个摆。它确实在空间中保持了其位置，首次清楚地证明了地球在旋转。他把自己的成就告诉了弗朗索瓦·阿拉戈，弗朗索瓦·阿拉戈请他在巴黎天文台重复这一实验。1851年2月3日，巴黎的每一位科学家都收到了到巴黎天文台观看这个摆的邀请。演示取得了圆满成功。傅科关于他的摆的论文由弗朗索瓦·阿拉戈在天文台进行实验的同一天向科学院宣读。在傅科提交的论文中，他未经证明地提出了他的正弦定律：

$T = 24/\sin q$

其中$T$是摆返回其原始位置所需的时间（以小时计），$q$是进行实验所在的纬度。因此，在两极，摆需要24小时才能返回其原始位置，而在赤道，它根本不旋转。2月17日，雅可·比内向科学院提交了一份完整报告，给出了正弦定律的完整数学论证。3月，普兰纳向都灵科学院提交了一篇关于傅科的摆的论文。约瑟·伯特兰写道[2]：

我们非常明确地说，因为这是真的，数学家们已经指明了方向；但我们补充说，因为这样做是公正的，他们并没有探索它。西莫恩·德尼·泊松曾令人遗憾地迅速决定它不值得考虑；正是傅科，在没有帮助或协助的情况下，第一个提出了它。

傅科接下来发明了陀螺仪，他这样做是为了以另一种方式证明地球的运动。同样，陀螺仪在空间中保持固定，而地球在运动。这是一项在傅科时代意义不大的发明，但当然今天我们在飞机、望远镜制导、爱德文·哈勃太空望远镜等方面认识到它的广泛用途。

法国此时的政治事件对傅科有利。他很有名，但除了担任Journal des Débats的科学编辑外，没有工作或收入。1851年12月2日，法国发生政变，路易-拿破仑·波拿巴掌握绝对权力并解散国民议会。整整一年后，他成为皇帝，称拿破仑三世。如果说法国科学界对没有受过正规科学训练的傅科有些轻视，那么拿破仑三世则不然，他本人就是一位业余科学家。他大力支持科学，尤其支持傅科，因此他安排专门为傅科设立了帝国天文台物理学家的职位。

帝国天文台——拿破仑三世对巴黎天文台的重新命名——的台长现在是于尔班·勒维耶。不久，傅科就在为天文台制造具有许多创新特性的精良望远镜。他做出了许多科学发现，还发明了许多其他机器来协助天文台的天文学家。他进行的一项测定光速的实验是到那时为止最为精确的，误差在半个百分点以内。

傅科于1860年陪同于尔班·勒维耶前往西班牙考察，观测7月18日的日食。他拍摄了一张日食照片。荣誉随即迅速降临到他身上：拿破仑三世于1862年授予他荣誉军团军官勋章；他于1862年当选为经度局成员；他当选为伦敦皇家学会会士；同时也是德国利奥波第那科学院成员；最后于1865年进入法国科学院，接替埃米尔·克拉佩龙。

到1867年10月，傅科开始感到双手麻木。尽管傅科的母亲努力帮助儿子康复，病情仍迅速恶化。这种疾病很可能是傅科一生中实验接触的化学物质，尤其是汞，所导致的结果。当然，正如我们在本传记开头所指出的，傅科的父亲早逝，所以遗传因素或许也起了作用。

Léon Foucault's father, Jean Léon Fortuné Foucault, was a publisher who had gained a fair reputation by publishing an excellent collection of volumes on the history of France. When Léon was young his father retired, since his health was rather poor, and the family moved from Paris to Nantes. However retirement did not result in any improvement in his father's health and he died in Nantes in 1829 when Léon was nine years old. His mother decided that they would return to Paris and from the age of ten Léon lived with his mother in a rather fine house on the junction of rue de Vangirard and rue d'Assas. The house is still there today and is marked by a commemorative plaque.

It was not only Léon's father who suffered from poor health, for Léon himself was a very frail child. He had one eye which was short-sighted and the other long-sighted. It gave him a rather awkward appearance and this was made worse by the fact that Léon became self-conscious about his appearance, tending to prefer being by himself. He was certainly given good educational opportunities by his mother who sent him to the Collège Stanislas but he did not seem to make the most of them. His teachers described him as lazy, he did not submit work on time, so that his mother had to employ tutors to educate him at home. Lissajous, who was about two and a half years younger than Foucault, was one of his few childhood friends. He wrote:-

Nothing about the boy announced that he would be illustrious some day; his health was delicate, his character mild, timid and not expansive. The frailty of his constitution and the slow way he worked made it impossible for him to study at college. He was only able to study successfully thanks to the help of dedicated tutors watched over by his mother.

Foucault did, however, make a good friend of one of the students at the Collège Stanislas, namely Hippolyte Fizeau.

If academic school work was not to Foucault's liking, he did begin to exhibit other talents. As a teenager he loved to construct toys and machines, some of which were really highly sophisticated such as a steam engine and a telegraph. His dexterity suggested to his mother than he would make a superb surgeon and so, having obtained his high school diploma, he entered medical school in Paris in 1839. At first he progressed well and his professor, Alfred Donné, was very pleased with his progress. However, on his first spell of hospital experience he saw some blood and fainted. After trying to overcome this problem, he realised that he would never be able to carry out medical duties and withdrew. Donné, however, wanted him to continue using his talents in the cause of medical science in a way that did not involve him coming in contact with patients, so he employed him as his assistant.

Just before starting work as Donné's assistant, Foucault had attended talks by Daguerre on his photographic methods. Foucault's friend Fizeau had been with him and the two experimented, improving the photographic process. Foucault combined his new photographic skills with his work for Donné and devised a method of taking photographs through a microscope. To do this he had to invent a powerful electric light source to illuminate the objects being photographed. In 1845 Foucault and Donné published A course of microscopy which contained 80 photographs of objects under a microscope.

Donné was the scientific editor of the Journal des Débats which was published daily. He retired from this position in 1845 handing over the task to Foucault. Bertrand in [2] writes about this task which Foucault carried out with remarkable success:-

At the age of 25, not having learnt anything at school nor from book, enthusiastic about science but not about study, Léon Foucault took on the task of making the work of scientists understandable to the public and of passing judgement on the value to the work of leading men of science. From the start he showed great subtlety, good judgement based on more prudence than would be expected. His first articles were remarkable; they were spiritual. He took his duties seriously. Launched, without any experience, into the highest level of science with all its confusion and problems, he was assured carrying out a role in which mediocrity would mean failure, with complete success.

... Always polite, yet seeking the truth, Foucault applied carefully considered judgements. Previously an unknown, this young man with no scientific publications nor known scientific discoveries, displayed a quiet authority and frankness which irritated many leading scientists.

Arago had learnt of Foucault's expertise with photography through a microscope on the publication of his book with Donné. He approached Foucault and Fizeau, whom he knew personally, in 1845 and asked if they could try to take photographs of the sun. They were successful in this and took the first ever photograph of the sun. It clearly shows a number of sunspots. Arago was delighted and saw the potential Foucault had to carry out other experiments for the Academy of Sciences. He next suggested that Foucault and Fizeau try to measure the speed of light in water. This was an experiment which Arago wanted to perform himself, but his failing eyesight meant that he could not undertake exacting experimental work himself. Shortly after beginning work using Arago's methods, Foucault and Fizeau had an argument. As a result they went their own ways, each attempting to carry out the experiment on their own.

Foucault now devised his own methods to approach the problem of measurement, building a steam engine to drive a spinning mirror. In April 1850 he showed that light travels slower in water than in air. This was in accordance with what the wave theory of light predicted, but contradicted what the corpuscular theory predicted. Foucault wrote [2]:-

I did not invent the spinning mirror, nor the achromatic lens, nor the network, nor the micrometer but I have had the good fortune to be able to put these instruments, devised by other scientists, together in such a way that I have solved a problem which was posed twelve years ago.

Foucault's next idea was that if he was able to design the support for a pendulum which allowed it to freely move in any direction without any resistance, then once set in motion it would retain its plane of swing in space while the Earth rotated beneath it. In January 1851 he succeeded in constructing such a pendulum in the basement of his house. It did indeed retain its position in space, demonstrating clearly for the first time that the Earth rotates. He told Arago of his achievement and Arago asked him to repeat it in the Paris Observatory. Every scientist in Paris received an invitation to view the pendulum in the Paris Observatory on 3 February 1851. The demonstration was a complete success. A paper by Foucault on his pendulum was read by Arago to the Academy of Sciences on the same day as the experiment was carried out in the Observatory. In the paper Foucault presented, without proof, his sine law:

$T = 24/\sin q$

where $T$ is the time in hours taken for the pendulum to return to its original position and $q$ is the latitude at which the experiment is carried out. So at the poles it takes 24 hours to return to its original position while at the equator it does not rotate at all. Binet presented a full report to the Academy of Sciences giving the full mathematical justification for the sine law on 17 February. Plana presented a paper to the Academy of Sciences of Turin on Foucault's pendulum in March. Bertrand writes [2]:-

We say very clearly, for it is true, that the mathematicians had shown the direction; but we add, for it is just to do so, that they had not explored it. Poisson had, deplorably quickly, decided its was not worth considering; and it was Foucault, without and help or assistance, who was the first to propose it.

Foucault next invented the gyroscope, which he did to demonstrate in yet another way the motion of the Earth. Again the gyroscope remains fixed in space while the Earth moves. It was an invention which was of little significance in Foucault's time, but of course today we recognise its widespread use in airplanes, guiding of telescopes, the Hubble space telescope etc.

Political events in France now worked to Foucault's advantage. He was famous, but had no job or income other than as science editor of the Journal des Débats. On 2 December 1851 there was a coup d'état in France with Louis-Napoléon Bonaparte assuming absolute power and dissolving the National Assembly. Exactly one year later he became Emperor taking the title Napoleon III. If the scientific community in France was somewhat dismissive of Foucault, who had no proper scientific training, then the same could not be said for Napoleon III who was himself an amateur scientist. He greatly supported science in general and Foucault in particular so he arranged the post of Physicist Attached to the Imperial Observatory to be specially created for Foucault.

The director of the Imperial Observatory, as Napoleon III had renamed the Paris Observatory, was now Le Verrier. Soon Foucault was creating superb telescopes for the Observatory with many innovative features. He made many scientific discoveries and invented many other machines to assist the astronomers at the Observatory. An experiment he carried out to determine the speed of light was by far the most accurate which had been carried out up to that time and was correct to within half of one percent.

Foucault accompanied Le Verrier on an expedition to Spain in 1860 to observe the eclipse on 18 July. He took a photograph of the eclipse. Honours were now quickly given to him: Napoleon III made him an Officer Légion d'Honneur in 1862; he was elected to the Bureau des Longitudes (1862); he was elected a fellow of the Royal Society of London; also a member of the German Academy of Sciences Leopoldina; and finally in 1865 the French Academy of Sciences where he replaced Clapeyron.

By October 1867 Foucault began to feel numbness in his hands. The illness progressed rapidly despite the efforts of Foucault's mother to help her son recover. It is likely that the illness was the result of the chemicals, in particular mercury, that Foucault had experimented with all his life. Of course, as we noted at the beginning of this biography, Foucault's father died young so perhaps hereditary factors also played a part.