威廉·皮耶克尼斯Vilhelm Bjerknes

威廉·皮耶克尼斯是卡尔·安东·皮耶克尼斯和Aletta Koren的儿子，Aletta Koren的父亲是西挪威教会的牧师。关于他家庭背景的更多细节，请参见卡尔·安东·皮耶克尼斯的传记。皮耶克尼斯的父亲卡尔不是一个好的实验家，因此当他还是个小男孩时，皮耶克尼斯做了很多工作，协助父亲进行实验，以验证父亲流体动力学研究中得出的理论预测。皮耶克尼斯在还很年幼时就开始与父亲一起做这项工作，并在1880年开始在克里斯蒂安尼亚大学读本科后继续合作。皮耶克尼斯于1882年写了他的第一篇论文New hydrodynamic investigations，当时他只有20岁。

我们应该注意到，Christiania或Kristiania的不同拼写并不是错误。当皮耶克尼斯在那里出生时，这座城市被命名为Christiania，1877年改为Kristiania，然后在1925年更名为奥斯陆。在皮耶克尼斯的一生中，他与这座有三个不同名字的城市联系在一起，这三个名字都出现在这本传记中。

1888年，皮耶克尼斯在克里斯蒂安尼亚大学学习数学和物理后获得硕士学位。在大学学习的最后几年，皮耶克尼斯决定必须结束与父亲的合作。此时卡尔·安东·皮耶克尼斯已变得离群索居，皮耶克尼斯认为继续合作会导致他自己的科学孤立。这对年轻的皮耶克尼斯来说一定是个痛苦的决定，他深爱着父亲，但他害怕陷入父亲发展出的工作模式，使自己置身于科学主流之外。这是一个成熟的决定，这位年轻人清楚地看到自己在未来的科学研究中要扮演重要角色。

从Kristiania毕业后，皮耶克尼斯获得了一项国家奖学金，这使他得以出国留学。他后来写道（同时想到自己和父亲）：-

……对于我们这种受限处境中任何希望发展成为科学人士的人来说，国外科学旅行是不可或缺的。

他于1889年前往巴黎，在那里听了儒勒·昂利·庞加莱关于电动力学的讲座，然后他前往波恩担任海因里希·鲁道夫·赫兹的助手。这不是一次短途旅行，因为皮耶克尼斯从1890年到1892年在波恩度过了两年。海因里希·鲁道夫·赫兹和皮耶克尼斯一起研究了电共振，这在无线电的发展中被证明很重要。从那时起，皮耶克尼斯一直是海因里希·鲁道夫·赫兹及其家人的亲密朋友。他回到挪威完成了他基于在波恩所做工作的博士论文。该博士学位于1892年授予，当时他三十岁。

1893年，皮耶克尼斯被任命为斯德哥尔摩Högskola（工程学院）的讲师，两年后，他成为斯德哥尔摩大学应用力学和数学物理教授。他继续发展父亲的思想，但也取得了其他重大进展，推广了开尔文和赫尔曼·冯·亥姆霍兹的结果。对皮耶克尼斯未来研究方向重要的是，他现在将他研究过的开尔文和赫尔曼·冯·亥姆霍兹涡旋理论的推广应用于大气和海洋的运动。皮耶克尼斯开始制定一项研究计划，他将使用流体动力学和热力学，以便在给定大气的特定状态时，能够计算其未来状态。

1893年，他与S H Bonnevie结婚，她出身于一个胡格诺派家庭，该家庭在迫害时期从法国逃到挪威。她曾是克里斯蒂安尼亚大学自然科学专业的学生。Gold写道[6]：-

她热情好客、亲切周到，对卑尔根气象学界愉快的社交氛围贡献不小……

他们有四个儿子。他们的儿子Jacob Bjerknes生于1897年11月2日。Jacob后来将与父亲合作，并凭借自身成就成为著名气象学家，发现了控制气旋行为的机制。

1905年，皮耶克尼斯访问美国，描述了他已在气团理论中采取的一些基本步骤，并解释了他将数学应用于天气预报的计划。卡内基基金会对此印象深刻，授予他资金以进行这项研究。他将继续从卡内基基金会获得这笔资助达36年。

1907年，皮耶克尼斯接受了克里斯蒂安尼亚大学应用力学和数学物理讲席。他与父亲非常不同，无论走到哪里，他都会聚集一大群合作者。他在克里斯蒂安尼亚建立了一个大型学派，研究动力气象学。

1912年，皮耶克尼斯获得了莱比锡大学地球物理学讲席的职位，以及正在筹建中的新莱比锡地球物理研究所所长的职位。他接受了这些职位，并带上了他在克里斯蒂安尼亚的一些合作者。不久，克里斯蒂安尼亚团队的其他成员以及他的儿子Jacob Bjerknes也加入了他的行列，后者在莱比锡期间也成为了合作者。Jacob和皮耶克尼斯合作在挪威建立了一个气象站网络，正是从这些气象站收集的数据导致了他们的极锋理论。

1917年，皮耶克尼斯获聘卑尔根大学讲席，并有机会创立卑尔根地球物理研究所。起初他相当不愿离开莱比锡，因为他担心那里地球物理研究所的长远未来，但一旦确信研究所的工作会继续下去，他便接受了卑尔根的聘请。尽管迁往卑尔根时已55岁，大多数历史学家都同意，皮耶克尼斯在那里做出了他最好的工作。这项关于以数学方法进行天气预报的工作在[2]中描述如下：-

将天气数值数据纳入可用于预报的数学公式的努力，早在本世纪初就在挪威地球物理研究所开始了。皮耶克尼斯及其在卑尔根的同事成功设计出关联可测量天气分量的方程，但其复杂性使得预报所需的快速求解无法实现。然而，从他们的努力中产生了关于气旋起源的极锋理论，以及如今熟悉的冷锋、暖锋和静止锋等表示气团前缘的名称……

数学方法上的下一步进展归功于刘易斯·弗赖伊·理查森，他在1922年将皮耶克尼斯的卑尔根学派所产生的复杂方程化简为长串简单算术运算。然而，在计算机出现之前，这些运算仍然无法在天气预报所需的时间尺度内求解。

皮耶克尼斯在这一领域的大部分主要成果都出现在On the Dynamics of the Circular Vortex with Applications to the Atmosphere and to Atmospheric Vortex and Wave Motion（1921）[1]中：-

这是他最优秀的著作之一，其中清晰阐述了他研究中最重要的基本思想。

有两位科学家是皮耶克尼斯最为钦佩的。一位是奥利弗·赫维赛德，另一位是海因里希·鲁道夫·赫兹。皮耶克尼斯曾于1919年在英格兰托基拜访过奥利弗·赫维赛德。那时奥利弗·赫维赛德在艰难的经济状况下过着孤独的生活，皮耶克尼斯尽力帮助他。在1922年写给奥利弗·赫维赛德的一封信中，皮耶克尼斯写道[6]：-

我很有可能不久就会写一些关于我的老师海因里希·鲁道夫·赫兹的东西，我曾在1890-91年在他的实验室工作。我是他极少数亲传弟子之一。这使我负有责任去回忆他的一些往事。我一直把他和你视为詹姆斯·克拉克·麦克斯韦的两位真正继承者，我非常高兴我有幸与这仅有的两位有过亲身接触。

1923年，皮耶克尼斯出版了一本关于电共振的论文集，并写了一篇导言，将它们献给海因里希·鲁道夫·赫兹以作纪念。

皮耶克尼斯在1926年做出了他最后的调动，接受了奥斯陆大学（克里斯蒂安尼亚于1925年更名为奥斯陆）应用力学和数学物理的讲席职位。他的工作当然不仅限于天气预报的数学，因为他继续研究他父亲开始的流体动力学工作。他还在1926年提出了太阳黑子是磁涡旋被太阳较差自转撕裂后的喷发端的理论。

在奥斯陆大学任职直至1932年退休期间，皮耶克尼斯在教学上投入了相当大的精力。他于1929年出版了一本关于向量分析的书，该书被设计为一部更大的理论物理学教科书的第一卷。这是一个他从未完成的项目，但[3]：-

……他机敏的头脑并未因年迈而迟钝，退休后很久仍继续工作。

1928年，皮耶克尼斯的妻子去世，当时她的妹妹Kristine Bonnevie教授成了他的管家。

如上文引述所示，皮耶克尼斯退休后仍然活跃。特别是他在1932年成为国际大地测量与地球物理学联合会气象学协会的主席。他于1936年在苏格兰爱丁堡组织了该协会的国际会议。他在1938年莱比锡地球物理研究所银禧庆典上发表了讲话，鼓励他们在天气预报问题上更加努力地工作。

次年，第二次世界大战爆发[6]：-

1939年战争的爆发对皮耶克尼斯是一个沉重的打击，因为他满怀国际友谊与合作的理想，并与德国和德国科学生活有着许多联系。在挪威被占领期间，他对入侵者表现出有尊严而勇敢的严厉态度。

1946年皮耶克尼斯84岁，他前往英国参加艾萨克·牛顿三百周年庆典。

Gold这样描述他的性格[6]：-

皮耶克尼斯举止庄重，外貌和科学工作的呈现方式亦然，但他的庄重之中融合着某种谦逊和热情，这既吸引又激励了年轻人。

他的学生之一T Bergeron补充道：-

[皮耶克尼斯]所拥有的敏锐幽默感，连同他的天才、他的远见，在漫长而迁徙的职业生涯中不断增长，使他成为一个非常人性化的人。但他确实有点害羞或压抑。

More than once I heard him state that he never learned easily, that he lacked the natural ability for easily communicating his thoughts verbally or in writing, that he had to be a hard worker - and certainly he was one。

皮耶克尼斯所获得的荣誉太多，无法在此一一列举，但我们提及一些。他当选为许多国家科学院院士，如奥斯陆的Norwegian Academy（1893年）、华盛顿科学院（1906年）、荷兰科学院（1923年）、Berlin Academy（1928年）、Royal Society of Edinburgh（1930年）、Royal Society of London（1933年）、U.S. National Academy of Science（1934年）和Accademia dei Lincei（1936年）。

他还获得了许多大学的荣誉学位，如圣安德鲁斯大学（1926年）和哥本哈根大学（1929年）。他获得的奖章包括阿加西海洋学奖章（1926年）、西蒙斯气象学奖章（1932年）和布伊-巴洛气象学奖章（1933年）。

Vilhelm Bjerknes was a son of Carl Bjerknes and Aletta Koren, whose father was a minister in the Church in West Norway. See the biography of Carl Bjerknes for more details of his family background. Carl, Vilhelm's father, was not a good experimentalist and so while he was a young boy Vilhelm did much work assisting his father in carrying out experiments to verify the theoretical predictions which came out of his father's hydrodynamic research. Vilhelm began this work with his father when he was still quite a young boy and he continued the collaboration after he began his undergraduate studies at the University of Kristiania in 1880. Vilhelm wrote his first paper New hydrodynamic investigations in 1882 when he was only 20 years old.

We should note that the different spelling of Christiania or Kristiania is not an error. The city was named Christiania when Vilhelm was born there, became Kristiania in 1877, then was renamed Oslo in 1925. Throughout Vilhelm Bjerknes's life he was associated with this city with its three different names and all three names appear in this biography.

In 1888 Vilhelm was awarded his Master's Degree from the University of Kristiania after studying mathematics and physics. During his final years of study at university Bjerknes decided that he would have to end the collaboration with his father. By this time Carl Bjerknes had become a recluse and continuing the collaboration would have led, Vilhelm believed, to his own scientific isolation. It must have been a painful decision for young Vilhelm, who was devoted to his father, but he feared falling into the pattern of work that his father had developed, leaving him outside the mainstream of science. It was a mature decision for the young man who clearly saw that he had a major role to play in the future of scientific research.

After graduating from Kristiania, Bjerknes was awarded a state scholarship which allowed him to study abroad. He later wrote (thinking about both himself and his father) that:-

... foreign scientific travels [were] indispensable for anyone in our restricted situation who wishes to develop into a man of science.

He went to Paris in 1889 where he attended Poincaré's lectures on electrodynamics, then he went to Bonn as Hertz's assistant. This was not a short trip, for Bjerknes spent two years from 1890 to 1892 in Bonn. Together Hertz and Bjerknes studied electrical resonance which proved important in the development of radio. Bjerknes remained a close friend of Hertz and his family from that time on. He returned to Norway to complete his doctoral thesis on work he had undertaken in Bonn. The doctorate was awarded in 1892 when he was thrity years old.

Bjerknes was appointed as a lecturer at the Högskola (School of Engineering) in Stockholm in 1893 then, two years later, he became professor of applied mechanics and mathematical physics at the University of Stockholm. He continued developing his father's ideas but also making other significant advances, generalising results of Thomson and Helmholtz. Important for the future direction of Bjerknes's research was the fact that he now applied the generalisation of the theory of vortices of Thomson and Helmholtz, which he had studied, to motions in the atmosphere and the ocean. Bjerknes began to work out a research plan that he would use hydrodynamics and thermodynamics so that, given a particular state of the atmosphere, he would be able to compute its future state.

In 1893 he married S H Bonnevie who came from a Huguenot family which had fled from France to Norway at the time of persecution. She was a student of natural sciences at the University of Christiania. Gold writes [6]:-

Her warm hearted and gracious hospitality contributed in no small degree to the happy social atmosphere of the meteorological community at Bergen ...

They had four sons. Their son, Jacob Bjerknes, was born on 2 November 1897. Jacob would later collaborate with his father and become a famous meteorologist in his own right, discovering the mechanism which controls the behaviour of cyclones.

In 1905 Vilhelm Bjerknes visited the United States, described some of the fundamental steps he had already taken in the theory of air masses, and explained his plans to apply mathematics to weather forecasting. The Carnegie Foundation were impressed and they awarded him funds to pursue this research. He was to continue to receive this grant from the Carnegie Foundation for 36 years.

Bjerknes accepted the chair of applied mechanics and mathematical physics at the University of Kristiania in 1907. He was a very different person from his father in that he gathered a large group of collaborators round him wherever he went. He built up a large school in Kristiania studying dynamic meteorology.

In 1912 Bjerknes was offered the chair of geophysics at the University of Leipzig, and also the directorship of the new Leipzig Geophysical Institute which was just being founded. He accepted the positions taking some of his collaborators from Kristiania with him. Soon he was joined by other members of the Kristiania team, and by his son Jacob Bjerknes who also became a collaborator during his time in Leipzig. Jacob and Vilhelm Bjerknes collaborated in establishing a network of weather stations in Norway and it was data gathered from these weather stations which led to their theory of polar fronts.

In 1917 Bjerknes was offered a chair at the University of Bergen and he was given the opportunity to found the Bergen Geophysical Institute. At first he was rather reluctant to leave Leipzig since he feared for the long-term future of the Geophysical Institute there but, once convinced that the work of the Institute would continue, he accepted the Bergen offer. Despite being 55 years old when he moved to Bergen, most historians agree that Bjerknes did his best work there. This work on a mathematical approach to weather forecasting is described in [2]:-

Efforts at incorporating numerical data on weather into mathematical formulas that could then be used for forecasting were initiated early in the century at the Norwegian Geophysical Institute. Vilhelm Bjerknes and his associates at Bergen succeeded in devising equations relating the measurable components of weather, but their complexity precluded the rapid solutions needed for forecasting. Out of their efforts, however, came the polar front theory for the origin of cyclones and the now-familiar names of cold front, warm front, and stationary front for the leading edges of air masses ...

The next step forward in the mathematical approach was due to Richardson in 1922 when he reduced the complicated equations produced by Bjerknes's Bergen School to long series of simple arithmetic operations. However, until the advent of computers, these were still impossible to solve in the time-scale required for weather forecasting.

Most of Bjerknes's major results in this area appear in On the Dynamics of the Circular Vortex with Applications to the Atmosphere and to Atmospheric Vortex and Wave Motion (1921) [1]:-

One of his finest books, it contains a clear explanation of the most important basic ideas in his research.

There were two scientists from whom Bjerknes had the greatest admiration. One was Heaviside and the other was Hertz. Bjerknes had visited Heaviside in 1919 in Torquay, England. By that time Heaviside was living a lonely life in hard financial circumstances and Bjerknes did his best to assist him. In a letter to Heaviside in 1922 Bjerknes wrote [6]:-

It is not unlikely that I shall write something presently of my old master Hertz in whose laboratory I worked in 1890-91. I am one of his very few personal pupils. this makes it a duty for me to bring some recollections of him. I have always considered him and you as the two real inheritors of Maxwell and I am very glad that I have had the good luck to come into personal contact with these two only ones.

In 1923 Bjerknes published a collection of papers on electrical resonance, and wrote an introduction dedicating them to the memory of Hertz.

Bjerknes made his final move in 1926 when he accepted the chair of applied mechanics and mathematical physics at the University of Oslo (Kristiania had been renamed Oslo in 1925). His work certainly was not confined to the mathematics of weather forecasting for he continued to study the hydrodynamical work started by his father. He also produced the theory, in 1926, that sun spots are the erupting ends of magnetic vortices broken by the sun's differential rotation.

During his years at the University of Oslo until his retirement in 1932 Bjerknes put a considerable effort into teaching. He published a book on vector analysis in 1929 which was designed as the first of a larger textbook on theoretical physics. It was a project which he never completed but [3]:-

... his alert mind was not dimmed by age, and he went on working long after his retirement.

In 1928 Bjerknes' wife died and at that time her sister, Professor Kristine Bonnevie, became his housekeeper.

As indicated in the above quote, Bjerknes remained active after his retirement. In particular he became President of the Association of Meteorology of the International Union of Geodesy and Geophysics in 1932. He organised the International Meeting of the Association in Edinburgh, Scotland, in 1936. He addressed the Silver Jubilee celebrations of the Leipzig Geophysical Institute in 1938, encouraging them to work harder on the problems of weather forecasting.

In the following year World War II broke out [6]:-

The outbreak of the war in 1939 was a sore blow to Bjerknes, imbued as he was with ideals of international friendship and cooperation and with his many ties with Germany and German scientific life. During the occupation of Norway he showed towards the invaders a dignified and courageous severity.

Although Bjerknes was 84 years old in 1946, he made the trip to the Newton Tercentenery Celebrations in England.

Gold writes of his character [6]:-

Bjerknes was dignified in manner, in appearance and in his presentation of his scientific work, but with his dignity he combined a certain modesty and an enthusiasm which both attracted and stimulated younger men.

T Bergeron, one of his students, added:-

The fine sense of humour which [Bjerknes] possessed, together with his genius, his far-sightedness, increased during a long and migrating career, made him a very human individual. But he was certainly a little shy or repressed.

More than once I heard him state that he never learned easily, that he lacked the natural ability for easily communicating his thoughts verbally or in writing, that he had to be a hard worker - and certainly he was one.

The honours which Bjerknes was awarded are far too numerous to list here, but we mention a few. He was elected to many national academies such as the Norwegian Academy of Oslo (1893), the Washington Academy of Science (1906), the Dutch Academy of Science (1923), the Berlin Academy (1928), the Royal Society of Edinburgh (1930), the Royal Society of London (1933), the U.S. National Academy of Science (1934), and the Accademia dei Lincei (1936).

He also received honorary degrees from many universities such as the University of St Andrews (1926) and the University of Copenhagen (1929). Among the Medal he received were the Agassiz Medal for Oceanography (1926), the Symons Medal for Meteorology (1932), and the Buy-Ballot Medal for Meteorology (1933).