威廉·维恩Wilhelm Wien

威廉·维恩是Carl Wien和卡罗琳·格茨的独生子，两人都出身于普鲁士贵族。正是他父母的社会体面感使他们给儿子取了六个名字。在后来的生活中，维恩被朋友和同事称为“威利”。Carl Wien是一位绅士农民和地主，维恩出生在菲施豪森附近加夫肯的家庭农场。当维恩两岁时，卡尔把家搬到东普鲁士拉斯滕堡附近的德拉亨施泰因农场，因为加夫肯的农场已无法养活他们。今天拉斯滕堡被称为肯琴，位于波兰东北部。在卡尔和Caroline Wien搬到德拉赫施泰因的同一年，维恩的表兄马克斯Carl Wien在圣诞节那天出生于柯尼斯堡。马克斯Carl Wien也成为了一名物理学家，研究高频波以及电解质在高电场强度下的行为。

维恩在成长过程中了解了农场的经营[1]：-

他经常与父亲一起骑马穿过田野，父亲因脊柱疾病而只能坐在马车里，因此维恩早早便了解了农业——在这方面，他的母亲承担了大部分责任。

当然，这样的成长环境并没有帮助他克服羞怯和与人相处的困难[1]：-

维恩与母亲特别亲近，母亲出色的历史和文学知识激发了他对这些学科的兴趣。他像父亲一样性格内向，幼年时没有交到朋友。他学会了骑马、游泳和滑冰；并且按照惯例，家里请了一位女士给他上法语私人课程，他在会写母语之前就会说法语了。

鉴于他害羞的性格和缺乏童年朋友，学校生活注定会很艰难，事实也确实如此。维恩于1875年开始在拉斯滕堡的文理中学上学，但对学业表现出很少的热情。他更喜欢在户外而不是在教室里，经常出去在周围的田野里漫步。他没有为在文理中学的学习做好充分准备，尤其是对数学课程准备不足。上了五年后，他的父母觉得他进步甚微，于是他在1880年离开文理中学回家，学习成为一名农民。然而，尤其是他的母亲渴望他获得一些学术技能，所以他的父母安排了私人教师。他的数学导师Switalski非常出色，维恩取得了良好的进步。随后他被送到柯尼斯堡老城文理中学学习，这是一所优秀的学校。当时阿诺·索末菲和赫尔曼·闵可夫斯基都是这所文理中学的学生，也许是他一生中第一次，维恩取得了良好的学业进步。他于1882年从高中毕业。

维恩的母亲鼓励他继续接受教育，在大学学习。他于1882年入读哥廷根大学，学习数学和自然科学，但对课程感到厌倦[1]：-

……由于性格独立，他觉得学生社团的奢华生活令人厌恶，仅一个学期后就离开了大学，游历莱茵兰和图林根。

这些旅行之后，他回到父母的农场，打算学习经营农场，以便能接替父母。然而，他的良好意图很快与不满情绪相冲突，因为他意识到自己必须接受大量培训来学习他不喜欢的技能。他决定再次尝试大学，并于1883年搬到柏林，在柏林大学继续他的教育。1883-84年冬天，当维恩开始在赫尔曼·冯·亥姆霍兹的实验室学习时，事情确实发生了变化。他后来谈到那时他：-

……真正第一次接触到物理学。

这一时期的多数德国学生会在不同大学之间流动，维恩遵循这一传统，于1884年夏季学期在海德堡大学度过。在这里，他从Georg Hermann Quincke那里学到了很多，Quincke是一位优秀的物理学家，曾在金属表面光的反射和电力方面做出过出色工作。在海德堡的这个学期之后，维恩回到柏林跟随赫尔曼·冯·亥姆霍兹学习，并被给予“光撞击光栅时的衍射”作为其博士论文的主题。维恩于1886年从柏林获得博士学位，但他在最终考试中的表现很差，得到了非常平庸的成绩。他于1886年夏天回到父母在德拉亨施泰因的农场，因为农场发生了一场严重火灾，摧毁了许多农场建筑。他能够帮助重建，并再次感到自己应该以务农为生。人们可能会期望他在柏林的教授们试图说服他继续从事物理学工作，但他们没有这样做，这加深了维恩的感觉，即也许他并不适合成为物理学家[1]：-

奥古斯特·孔特于1888年在柏林大学接替赫尔曼·冯·亥姆霍兹的职位，而赫尔曼·冯·亥姆霍兹本人同时被任命为新成立的帝国物理技术研究所的首任所长，他们强化了维恩对物理学的疑虑，坚持认为作为独子他应当接管父母的财产；如果他愿意，他可以始终将科学研究作为业余爱好。

维恩处境困难，对自己的物理学能力没有把握，但始终非常清楚自己缺乏接管经营农场的技能。他发现与农场工人沟通很困难，而且他没有所需的讨价还价技巧，甚至连买一匹马都买不好。尽管如此，他听从了教授们的建议，在三年多的时间里务农，将物理学研究作为业余爱好。他确实设法在柏林与赫尔曼·冯·亥姆霍兹度过了一个学期，但除此之外他是一名全职农民。然而，命运介入，阻止了维恩作为一个不快乐的无能农民度过余生。这就是1890年的一场大旱，导致维恩的父母——此时已相当年迈且健康状况不佳——卖掉了他们的农场。到1890年春天，维恩在柏林-夏洛滕堡的帝国物理技术研究所担任赫尔曼·冯·亥姆霍兹的助手。他的父母搬到了柏林-韦斯滕德，但他的母亲病得很重，而他的父亲多年来一直重病缠身，于次年去世。1890年，俾斯麦被皇帝免职，维恩真切地感到一个新时代为他开启了。在接下来的几年里，他开展了质量卓越的工作，这为他赢得了诺贝尔物理学奖，但在1890年，他的首要任务是撰写一篇教授资格论文（Habilitation）论文[3]：-

维恩于1890年写信给海因里希·鲁道夫·赫兹，询问他对自己所进行的关于能量定域化问题的研究的看法。他告诉海因里希·鲁道夫·赫兹，像坡印廷和洛奇一样，他想赋予能量以类似于物质的属性。他的指导性思想是能量的各个部分具有可追踪的运动；他的老师赫尔曼·冯·亥姆霍兹不喜欢这个想法，而维恩现在试图在海因里希·鲁道夫·赫兹身上试验它。

海因里希·鲁道夫·赫兹像赫尔曼·冯·亥姆霍兹一样，对维恩的想法并不特别热衷，但他在能量定域化方面的工作使他在1892年获得了柏林大学的任教资格。然而，回到1890年，维恩向德国协会的物理学分会报告了能量理论的当前状况。他的报告的详细内容见[3]。

维恩1890年的报告见THIS LINK。

在他1892年的任教资格论文[1]中：-

维恩非常一般地将J·H·坡印廷的电流“能流”与辐射熵的概念联系起来。此外，通过与运动物质位置的连续变化相类比，他还确立了电动力学辐射能量的运动，探究了海因里希·鲁道夫·赫兹提出的问题，即这种能量在运动过程中究竟能否被定域化。

在维恩于物理技术帝国研究所最初几年的工作中，能量局域化并非他研究的唯一课题。他进行了一系列不成功的实验，使用铂箔，试图建立一种新的光单位[1]：-

正是这种对理论与实验的双重关注，埋下了维恩成长为一位罕见物理学家的种子——他对这两个领域都拥有同样出色的知识。

1893年，维恩提出了不同温度下黑体辐射谱的位移定律。他的方法在[2]中有所描述：-

[维恩的]想法是用一个带小孔的炉子作为理想黑体的良好近似。任何进入小孔的辐射都会在炉子内壁上被散射和反射如此多次，以至于几乎所有入射辐射都被吸收，而其中一部分再次找到出路离开小孔的机会可以被弄得极其微小。从这个小孔出来的辐射于是非常接近对应于炉温的平衡黑体电磁辐射。

维恩推导出一个辐射分布定律，并于1896年6月发表。马克斯·普朗克在维恩进行这项工作时是他的同事，后来在1900年，quantum theory基于这样一个事实：维恩的定律虽然在高频下有效，但在低频下完全失效。马克斯·普朗克在1900年提出了维恩定律的一个更复杂的版本。维恩因其在热辐射方面的工作获得了1911年诺贝尔奖。在他的诺贝尔演讲中，他解释了他的“思想实验”方法，这种方法在物理学研究中已被证明如此富有成果[12]：-

利用已知的物理定律，可以推导出一个普遍的辐射理论定律，该定律以位移定律之名受到同行工作者的赞誉。在将热力学应用于辐射理论时，我们利用了在其他地方已被证明如此富有成果的理想过程。这些是思想实验，其实现往往不切实际，然而却能得出可靠的结果。只有当我们知道了受定律支配、思想实验所依据的所有过程，从而能够准确而完整地陈述任何变化的效果时，才能进行这样的思考。此外，为了能够理想化，我们必须忽略所有非本质的次级现象，而只考虑与所考察过程不可分割地联系在一起的一切。在机械热理论的应用中，这种方法已被证明极其富有成果。

1892年，维恩在柏林晋升为讲师，他在物理技术帝国研究所工作得很愉快，但1894年赫尔曼·冯·亥姆霍兹去世，弗里德里希·科尔劳施被任命接替他的职位。科尔劳施对于如何管理物理技术帝国研究所有非常明确的想法，制定了非常具体和僵化的研究计划。这当然不符合维恩那种由他极其独立的性格所决定的做事方式。因此，当他在1896年收到亚琛莱茵-威斯特法伦技术大学（RWTH Aachen）的教授职位邀请时，他欣然接受了这一职位。在亚琛，维恩遇到了路易丝·梅勒；他们于1898年结婚，有两个儿子，沃尔特劳特和卡尔，以及两个女儿，格尔达和希尔德加德。维恩被任命填补先前由菲利普·爱德华·安东·勒纳占据的讲席，勒纳已离开亚琛去海德堡担任讲席。勒纳曾在亚琛进行阴极射线的研究，他使用的设备对维恩极为有用，后者在柏林时已开始进行阴极射线的研究。事实上，勒纳因对阴极射线的研究及其许多特性的发现而获得了1905年诺贝尔物理学奖。

1898年，在研究电离气体流时，维恩识别出一种质量与氢原子相等的正粒子。维恩发明了第一台质谱仪，并通过这项工作奠定了质谱学的基础。然而，将维恩的质谱仪结果与原子和电子理论协调起来存在困难。J J Thomson改进了维恩的装置，并在1913年进行了进一步的实验，然后在E 卢瑟福于1919年的工作之后，维恩的粒子被接受并命名为质子。他对晶体使x射线衍射的研究是该领域最早的工作，比Max von Laue的发现早五年。

在亚琛待了三年后，维恩于1899年转到吉森大学，被任命为正教授。然而，他在吉森只待了六个月，就接受了维尔茨堡大学的正教授职位，并在那里度过了接下来的二十年。该讲席因维恩Conrad Röntgen转任慕尼黑的一个讲席而空缺。维恩此时已是一位国际知名的物理学家，收到了世界各地的许多讲学邀请。他访问过的国家包括1904年的挪威、西班牙、意大利和英国，1912年的希腊，以及1918年的波罗的海地区，在那里他做了几次讲座。1913年春天，他访问了美国，在哥伦比亚大学讲学，还访问了哈佛和耶鲁。他借此机会在华盛顿拜访了Arthur Day，他也是一位物理学家，是Friedrich Kohlrausch的女婿。在维尔茨堡，维恩允许自己花时间沉迷于物理学之外的其他兴趣。他花时间研究历史、外国文学和美术，这些是他从母亲激发他兴趣时起就一直热爱的学科。

在[8]中，描述了阿尔伯特·爱因斯坦写给维恩的一封信，信中他请求维恩对阿尔伯特·爱因斯坦在1907年纯粹从理论考虑提出的等效原理进行实验证明：-

1912年，[阿尔伯特·爱因斯坦]通过信件转向W 维恩，请求测量由铀和铅制成的摆的振动周期之间的差异，以及分别用扭秤测量铀和铅重物的惯性质量与引力质量的比例关系。这封信证明阿尔伯特·爱因斯坦在表述等效原理时并不知道厄特沃什·罗兰实验……

1914年，维恩出版了Ziele und Methoden der theoetische Physik Ⓣ（理论物理学的目标和方法）。在这部著作中，他阐述了自己关于数学物理与理论物理之间差异的观点。他写道[1]：-

……应提供数学工具——正如数学建立数值量之间的精确关系一样。……[理论物理学]应寻求确定定量定律，为此它必须发展假说；然而，它只能达到近似的精确性。

他在这部著作中还声称，自然定律比科学家们认识到的更简单，因为他们只能看到定律效应的无限多样性[1]：-

只有通过与观测数据的比较进行定量验证，才能保护理论家——他们通常不觉得自己受实验约束——免受自己产生的许多不合适的想法的影响。这种理论与实验之间受定量控制的相互作用，排除了在使用数学表达式时可能出现的疏忽。

第一次世界大战对维恩影响很大，但战争结束后发生的事件更让他不安。对德国的封锁并未解除，食物和燃料极度短缺，从前线返回的士兵饥肠辘辘，没有工作，对自己的处境心怀怨恨。在苏俄的鼓励下，德国共产党中的布尔什维克利用这种不满情绪推动革命。他们鼓动1918年12月的示威活动，进而导致1919年1月在柏林发生了一场未遂革命。革命失败了，但反对布尔什维克的斗争所造成的局面让维恩深感不快。20世纪20年代，各种不同的问题使维恩对自己的祖国持续感到悲伤。在1927年5月1日写给埃尔温·薛定谔的一封信中，他担心：

……如今在欧洲发生的、生活各个方面的美国化侵蚀。

在维尔茨堡待了20年后，维恩于1920年接受了慕尼黑大学提供的讲席。在那里，他建了一座新的物理研究所，并在大学中发挥了重要作用，于1925至1926年被任命为校长。

1905年至1918年间，维恩和马克斯·普朗克编辑了Annalen der Physik。他们必须对正在改变物理学面貌的相对论新发现采取一种方针，因此他们寻求发表阐明相对论物理意义或概念的论文；他们把强调数学解释的手稿留给哥廷根的数学家同事们。维恩继续担任Annalen der Physik的编辑，直到去世。他还是F·哈姆斯共同编辑的Handbuch der Experimental Physik的编辑。

维恩荣幸地当选为柏林科学院、Göttingen Academy of Sciences、Austrian Academy of Sciences、Swedish Academy of Sciences、Norwegian Academy of Science and Letters以及华盛顿的国家科学院的成员，他还被选为美因河畔法兰克福物理学会的荣誉会员。

维恩的同事马克斯·普朗克写道：

恐怕只有极少数物理学家能像Willy维恩那样，在自己特定领域的实验和理论两方面都同样精通，而且将来一位科学家要做出像热辐射位移定律和极隧射线本质定律这样性质多样的发现，会变得越来越罕见。

阴极射线由阴极射线管产生，并且如上所述，维恩证明它们由带正电的粒子组成，其质量与氢原子相同。今天这些粒子被称为质子。

Wilhelm Wien was the only child of Carl Wien and Caroline Gertz who were both of noble Prussian birth. It was his parents' sense of social propriety that made them give their son six given names. In later life, Wilhelm Wien was known as 'Willy' to his friends and colleagues. Carl Wien was a gentleman farmer and landowner, and Wilhelm was born on the family farm at Gaffken near Fischhausen. Carl took his family to a farm at Drachenstein, near Rastenburg in East Prussia, when Wilhelm was two years old since the one at Gaffken could no longer support them. Today Rastenburg is known as Ketrzyn and it is in northeast Poland. In the same year that Carl and Caroline Wien moved to Drachstein, Wilhelm's cousin Max Carl Wien was born on Christmas day in Königsberg. Max Carl Wien also became a physicist and worked on high-frequency waves and the behaviour of electrolytes at high electric field strengths.

Wilhelm grew up learning about the running of the farm [1]:-

He frequently rode through the fields with his father, who was confined to a wagon because of a spinal ailment, and thus Wien early learned about agriculture - in which his mother assumed the bulk of the responsibilities.

Certainly it was an upbringing which did not help him to overcome his shyness and difficulty with others [1]:-

Wien was especially close to his mother, whose excellent knowledge of history and literature stimulated his interests in the subjects. An introvert, like his father, he made no friends during his early childhood. He learned to ride, swim and skate; and, as was customary, a woman was engaged to give him private lessons in French, which he spoke before he could write his native language.

Given his shy personality and lack of childhood friends, school was always going to prove difficult and this indeed was the case. Wilhelm Wien attended the Gymnasium in Rastenburg beginning in 1875 but showed little enthusiasm for academic work. He preferred to be outside rather than in a classroom and often went off to wander in the surrounding fields. He had not been well prepared for study at the Gymnasium and he was particularly poorly prepared for the mathematics courses. After attending for five years, his parents felt that he was making little progress so he left the Gymnasium to return home in 1880 to learn to become a farmer. However, his mother in particular was keen for him to gain some academic skills so his parents arranged private tutors. His mathematics tutor Switalski was outstanding and Wien made good progress. He was then sent to study at the Königsberg Altstädtisches Gymnasium which was an excellent school. Arnold Sommerfeld and Hermann Minkowski were both pupils at this Gymnasium at the time and, perhaps for the first time in his life, Wien made good academic progress. He graduated from the high school in 1882.

Wien's mother encouraged him to continue his education with study at university. He enrolled in 1882 at the University of Göttingen where he studied mathematics and natural sciences but became bored with the courses [1]:-

... being of an independent spirit, he found the lavish life of the student societies distasteful and left the university after only one semester to travel through the Rhineland and Thüringen.

After these travels he returned to his parents' farm with the intention of learning to run the farm so that he could take over from his parents. His good intentions, however, soon were competing with a feeling of discontentment as he realised that he would have to undergo much training to learn skills which he did not find pleasing. He decided to try university again and in 1883 he moved to Berlin where he continued his education at the university. Things certainly changed for Wien in the winter of 1883-84 when he began studying in the laboratory of Hermann von Helmholtz. He later said at that time he:-

... really came in contact with physics for the first time.

Most German students of this period would move between different universities and Wien followed this tradition by spending the summer semester of 1884 at the University of Heidelberg. Here he learnt much taking a course from Georg Hermann Quincke, an excellent physicist who had done good work on the reflection of light from metallic surfaces and on electric forces. After this semester at Heidelberg, Wien returned to study with Helmholtz in Berlin and was given the topic of 'diffraction of light when it strikes a grating' as the subject for his doctoral dissertation. Wien was awarded his doctorate from Berlin in 1886 but his performance is the final examination was poor and he was given a very mediocre grade. He returned to his parents' farm at Drachenstein in the summer of 1886 since there had been a serious fire at the farm which had destroyed many of the farm buildings. He was able to help with rebuilding and again he felt that he should make farming his life. One might have expected his professors at Berlin to try to persuade him to continue working in physics but they did not do so, adding to Wien's feeling that perhaps he was not cut out to be a physicist [1]:-

August Kundt, who in 1888 became Helmholtz's successor at the University of Berlin, and Helmholtz himself, who at the same time had been appointed the first president of the newly founded Physikalisch-Technische Reichsanstalt, reinforced Wien's doubts about physics, maintaining that as an only son he should take over his parents' property; if he wished, he could always pursue scientific research as a hobby.

Poor Wien was in a difficult position, unsure of his abilities in physics, but always very sure of his lack of skill for taking over running the farm. He found communicating with the farm workers difficult and he did not have the required bartering skill to even make a good purchase of a horse. Despite this he took his professors' advice and for over three years he worked as a farmer, doing research in physics as a hobby. He did manage to spend one semester with Helmholtz in Berlin but except for this he was a full-time farmer. However, fate intervened and stopped Wien spending the rest of his life as an unhappy incompetent farmer. This was in the form of a major drought in 1890 which led to Wien's parents, now quite old and in poor health, selling their farm. By the spring of 1890 Wien was working as Helmholtz's assistant at the Physikalisch-Technische Reichsanstalt in Berlin-Charlottenburg. His parents moved to Berlin-Westend, but his mother took seriously ill and his father, seriously ill for many years, died in the following year. In 1890 Bismarck was dismissed as Emperor and Wien really felt that a new era had opened up for him. Over the next few years he carried out work of exceptional quality which led to the award of a Nobel Prize in physics but in 1890 his first priority was to work on an habilitation thesis [3]:-

Wien wrote to Heinrich Hertz in 1890 to ask his opinion of research he had undertaken into the question of the localisation of energy. He told Hertz that, like Poynting and Lodge, he wanted to endow energy with properties analogous to those of matter. His guiding idea was that the individual parts of energy have a traceable motion; his teacher Helmholtz did not like the idea, and Wien now tried it out on Hertz.

Heinrich Hertz was, like Helmholtz, not particularly enthusiastic about Wien's ideas but his work on the localisation of energy led to his habilitation in Berlin in 1892. However, returning to 1890, Wien reported on the current state of the theory of energy to the physics section of the German Association. Details of his report are given in [3].

Wien's 1890 report is at THIS LINK.

In his habilitation dissertation of 1892 [1]:-

Wien linked, very generally, J H Poynting's 'energy flux' of electric currents with the concept of the entropy of radiation. Further, by analogy with the continuous change of position of matter in motion, he also established the motion of the energy of electrodynamic radiation, pursuing the question raised by Hertz of whether this energy can be localised at all during movement.

The localisation of energy was not the only topic that Wien worked on in his first years at the Physikalisch-Technische Reichsanstalt. He conducted an unsuccessful series of experiments, using platinum foil, trying to establish a new unit of light [1]:-

In this dual concern with theory and experiment lay the seed of Wien's development into the rare physicist who possesses equally good knowledge of both areas.

In 1893 Wien stated his displacement law of blackbody radiation spectra at different temperatures. His method is described in [2]:-

It was [Wien's] idea to use as a good approximation for the ideal blackbody an oven with a small hole. Any radiation that enters the small hole is scattered and reflected from the inner walls of the oven so often that nearly all incoming radiation is absorbed and the chance of some of it finding its way out of the hole again can be made exceedingly small. The radiation coming out of this hole is then very close to the equilibrium blackbody electromagnetic radiation corresponding to the oven temperature.

Next Wien derived a distribution law of radiation which he published in June 1896. Max Planck, who was a colleague of Wien's when he was carrying out this work, later, in 1900, based quantum theory on the fact that Wien's law, while valid at high frequencies, broke down completely at low frequencies. Planck suggested a more complicated version of Wien's law in 1900. Wien received the 1911 Nobel Prize for his work on heat radiation. In his Nobel lecture he explained his 'thought experiment' approach which has proved so fruitful in physics research [12]:-

Using known physical laws it was possible to derive a general law of radiation theory which has, under the name of the displacement law, been acclaimed by fellow workers. In applying thermodynamics to the theory of radiation, we make use of the ideal processes which have been found so fruitful elsewhere. These are mental experiments whose realization is frequently impracticable and which nevertheless lead to reliable results. Such deliberations can only be undertaken if all the processes on which, governed by laws, the mental experiments are based, are known, so that the effect of any change can be stated accurately and completely. Further, to be allowed to idealize, we must neglect all non-essential secondary phenomena, while considering only everything indissolubly connected with the processes under examination. In the application of mechanical heat theory, this method has proved to be extremely fruitful.

In 1892 Wien had been promoted to a lecturer in Berlin and he was happy working at the Physikalisch-Technische Reichsanstalt but in 1894 Helmholtz died and Friedrich Kohlrausch was appointed to succeed him. Kohlrausch had very definite ideas about how he should run the Physikalisch-Technische Reichsanstalt, drawing up very specific and rigid research plans. This certainly did not fit in with Wien's approach determined by his extremely independent nature. When, therefore, he received an offer in 1896 of a professorship at the Rhenish-Westphalian Technical University of Aachen (RWTH Aachen) he was delighted to accept the position. In Aachen, Wien met Luise Mehler; they married in 1898 and had two sons, Waltraut and Karl, and two daughters, Gerda and Hildegard. Wien had been appointed to fill the chair previously held by Philipp Eduard Anton Lenard who had left Aachen to take up the chair at Heidelberg. Lenard had been undertaking research on cathode rays in Aachen and the equipment he had been using proved extremely useful to Wien who had begun to undertake research into cathode rays while in Berlin. In fact Lenard was awarded the 1905 Nobel Prize for Physics for his research on cathode rays and his discovery of many of their properties.

While studying streams of ionized gas in 1898, Wien identified a positive particle equal in mass to the hydrogen atom. Wien invented the first mass-spectrograph and, with this work, laid the foundation of mass spectroscopy. However, there were difficulties in reconciling the results from Wien's mass-spectrograph with the theories of atoms and electrons. J J Thomson refined Wien's apparatus and conducted further experiments in 1913 then, after work by E Rutherford in 1919, Wien's particle was accepted and named the proton. His studies on the diffraction of x-rays by crystals was the earliest work in this area, coming five years before the discoveries made by Max von Laue.

After three years in Aachen, Wien moved to the University of Giessen in 1899 where he was appointed as a full professor. However, he spent only six months in Giessen before accepting a full professorship at the University of Würzburg where he spent the next twenty years. The chair had become vacant due to Wilhelm Conrad Röntgen moving to a chair at Munich. Wien was now an internationally acclaimed physicist and received many invitations to lecture throughout the world. Among the countries he visited were Norway, Spain, Italy and England in 1904, Greece in 1912 and the Baltic region in 1918 where he gave several lectures. In spring 1913 he visited the United States, lecturing at Columbia University and also visiting Harvard and Yale. He took the opportunity to visit Arthur Day, also a physicist and Friedrich Kohlrausch's son-in-law, in Washington. At Würzburg, Wien allowed himself the time to indulge in other interests besides physics. He spent time studying history, foreign literature and fine arts, subjects that he had loved from the time that his mother had enthused him.

In [8] a letter from Einstein to Wien is described in which he asks Wien to conduct an experimental proof of the principle of equivalence which Einstein had proposed from purely theoretical considerations in 1907:-

In 1912 [Einstein] turned by letter to W Wien with the request to measure the difference between the periods of oscillation of pendulums made of uranium and lead, as well as the proportionality of inertial and gravitational masses of a uranium and a lead weight, respectively, namely with a torsion balance. The letter testifies that Einstein was not aware of the Eötvös experiment when he formulated the principle of equivalence ...

In 1914 Wien published Ziele und Methoden der theoetische Physik Ⓣ. In this work he gave his views on the difference between mathematical physics and theoretical physics. Mathematical physics, he wrote [1]:-

... should furnish the mathematical tools - just as mathematics establishes exact relationships between numerical quantities. ... [Theoretical physics] should seek to determine quantitative laws, for which it must develop hypotheses; it can, however, attain only approximate exactness.

He also claimed in this work that the laws of nature are simpler than scientists realise for they only can see the infinite variety of the effects of the laws [1]:-

Only quantitative verification through comparison with observed data can protect the theoretician - who generally does not feel bound by experiments - from the many unsuitable ideas he generates. This quantitatively controlled interaction between theory and experiment excludes possible carelessness in the use of mathematical expressions.

World War I greatly affected Wien, but the events which followed the end of the war disturbed him even more. The blockade of Germany was not lifted, food and fuel were in very short supply, soldiers returning from the front were left hungry, without jobs, and bitter about their situation. The Bolsheviks in the Communist Party of Germany, encouraged by Soviet Russia, took advantage of the discontent and pushed for a revolution. They encouraged demonstrations in December 1918 that led to an attempted revolution in Berlin in January 1919. It failed, but the struggle against the Bolsheviks provided a situation which left Wien deeply unhappy. During the 1920s there were different problems which resulted in Wien's continuing sadness about his native land. In a letter to Schrödinger written on 1 May 1927 he feared:-

... the encroaching Americanisation of all of life that is now taking place in Europe.

After 20 years in Würzburg, Wien accepted an offer of a chair from the University of Munich in 1920. There he had a new physics institute built and played a major role in the university, being appointed rector in 1925-26.

Between 1905 and 1918 Wien and Planck edited the Annalen der Physik. They had to adopt a policy towards the new discoveries of relativity which were changing the face of physics so they sought to publish papers that illuminated the physical meaning or concepts of relativity; they left manuscripts that stressed mathematical interpretations to their mathematician colleagues in Göttingen. Wien continued as an editor of Annalen der Physik until his death. He was also a joint editor, with F Harms, of the Handbuch der Experimental Physik.

Wien was honoured with election to the Berlin Academy of Science, the Göttingen Academy of Sciences, the Austrian Academy of Sciences, the Swedish Academy of Sciences, the Norwegian Academy of Science and Letters, and the National Academy of Sciences in Washington, and he was also made an honorary member of the Physical Society of Frankfurt-on-Main

Max Planck, who was a colleague of Wien's, wrote:-

There are probably only very few physicists who are equally expert in both the experimental and theoretical sides of their own particular field as Willy Wien, and in the future it will become more and more rare for one scientist to make discoveries of such a varied nature as that of the law for the displacement of thermal radiation and the one on the nature of canal rays.

Canal rays were produced by cathode ray tubes and, as we explained above, were shown by Wien to consist of positively charged particles with the same mass as hydrogen atoms. Today these particles are called protons.