诺贝尔奖获得者全书【1919】【物理学奖】
【获奖类别】物理学奖【获奖年代】1919年
【获得情况】约翰尼斯·斯塔克（Johannes Stark）
[img]http://nobelprize.org/physics/laureates/1919/stark.jpg[/img]
约翰尼斯·斯塔克（Johannes Stark）
斯塔克1874年4月15日出生于德国巴伐利亚的希根霍夫
1957年6月21日斯塔克在德国上巴伐利亚去世
【获奖理由】因发现极隧射线的多普勒效应和在电场作用下光谱线的分裂现象，斯塔克（Johannes Stark 1874~1957）获得了1919年度诺贝尔物理学奖。
【研究成果】
极隧射线就是气体导电过程中产生的正离子。这些离子在外加电压的作用下射向阴极，并穿过阴极孔（隧道）。斯塔克（右图）发现了这些高速运动离子所辐射的光的频率移动。他曾说过，他几乎没费吹灰之力就发现了氢谱线的移动。他曾试图将他发现的这种光的多普勒效应作为爱因斯坦狭义相对论的一个证明，1907年他又想将其作为量子假设的证据，但奇怪的是，1913年后他又强烈地反对量子论和相对论。
1913年，他第一个发现了斯塔克效应。所谓斯塔克效应，是指强电场中原子发射的谱线在电场影响下出现分裂成几条的现象。具体地讲，就是在电场强度约为100万伏/厘米时，原子发射的谱线的图案是对称的，其间隔大小与电场强度成正比。在此之前，塞曼等科学家也做过此类研究，但都失败了。斯塔克在凿孔阴极后仅几毫米处放置了第三个极板，并在这两极之间加了2万伏/厘米的电场，然后用分光计在垂直于射线的方向上测试，观察到了光谱线的分裂。1916年，爱泼斯坦（Epstein）把斯塔克效应纳入了量子力学的框架。1926年，薛定谔证明了这一效应与波动力学是一致的。
【获奖感言】
极隧射线是哥尔茨坦在1886年在含稀薄气体的放电管中发现的，这种射线后来证明主要是由放电管中带正电的气体原子组成的，这些带正电的原子在电场的作用下以很高的速度沿着射线束运动。
1902年斯塔克预言，极隧射线粒子在运动过程中，不断与管子中气体分子碰撞，如果动能足够大，应该产生发光现象，发出的光谱会因多普勒效应而改变频率，例如，如果射线朝着观察者方向运动，则观察到的光谱线应向紫端移动，其位移会随速度的增大而增大，由此可以确定极隧射线粒子的速度。
1905年斯塔克果然在含氢的极隧射线管中发现了这种多普勒效应。随后他在其它一些化学元素的极隧射线中也证明有上述效应。
斯塔克这一发现有助于确定极隧射线的本质，他证明了这种射线的粒子是发光原子或原子离子。斯塔克和他的学生们进一步研究了多普勒效应的光谱，取得了重要成果，不仅包括极隧射线本身及其形成，还包括同一种化学元素在不同条件下发射的不同光谱的性质。
斯塔克还研究了含有氢气的管子中极隧射线通过强电场的情况。1913年他在研究过程中观察到氢谱线加宽了。他立即联想到十几年前塞曼（P.Zeeman）的发现。这会不会是与塞曼效应对应的一种电学现象？从1896年塞曼发现谱线的磁致分裂以来，科学家经常提出这样的问题：既然在磁场中原子发出的光谱线会分裂，在电场中会不会有类似现象？然而，德国的福格特（W.W.Voigt）试图从束缚电子发射光谱的理论推导电场对光谱的作用。计算结果表明，即使加300V/cm的静电场，光谱线的分裂也只有钠黄光的D双线间隔的5×10-5。这一效应太小了，实在难以观察。于是福格特认为，这就解释了为什么以前没有人发现与塞曼效应对应的电现象。多年来，他的解释妨碍了人们研究这一效应的积极性。到了1913年，对量子理论起过先导作用的斯塔克对这个问题发生了兴趣，他认为福格特的经典理论不足为凭。在他看来，光谱的发射是由于价电子的跃迁，电场一定会改变原子内部电荷的分布，从而影响发射频率。他是研究极隧射线的专家。他在极隧射线管子中的阴极和另一辅助电极之间加上强电场，强度达到31kV/cm。然后沿平行于或垂直于电场的方向用光谱仪进行观测。氢的极隧射线穿过电场，果然观测到了加宽。经过仔细调整，他终于获得了谱线分裂的证据，并且证明随着谱线序号的增大，分裂的数目也随之增多。他还发现，沿电力线成直角的方向观察，所有的分量都是平面偏振光，外面的两根较强，其电矢量与电场平行；中间的几根较弱，其电矢量与电场垂直。他的观测非常精细，得出了如下的结论：各分量到中心线的距离是最小位移的整数倍，而最小位移对所有谱线均相同；位移与电场强度直接成正比。
应该肯定，斯塔克发现光谱线的电致分裂对原子物理学的发展有重要意义。人们把这一现象称为斯塔克效应，并于1919年在爱因斯坦和玻尔之前就授予他诺贝尔物理学奖。
斯塔克效应对玻尔的原子理论起了一定的验证作用。1914年玻尔在卢瑟福的启示下，对斯塔克效应作了理论分析，他把斯塔克效应看成是外电场改变了电子在自由原子中的轨道引起的现象，从自己的原子模型出发，推出了氢谱线电致分裂的最大频率位移。但是计算结果与实际测量分歧甚大。瓦伯（E.Warburg）则在玻尔的频率公式上加一修正项，这一修正项相当于电子恢复到原有轨道所需作的功，加了修正项之后就可以满意地解释斯塔克效应。而索末菲的相对论性原子理论则更为理想，他的学生埃普斯坦（P.S，Epstein）根据索末菲的理论推得谱线电场分裂公式。后来索末菲提出选择定则，并总结出一套经验规则，结果与斯塔克的观测相符很好。当然斯塔克效应十分复杂，准确的解释有待于量子力学的出现和原子理论的进一步发展。
【其它事件】
纳粹分子？诺贝尔奖得主？
的确，很难将凶残、狂热的纳粹分子和崇高的诺贝尔科学奖挂起钩来。但是，从实质上讲，我们不得不承认科学上的造诣和成就并不能代表一个科学家人格和品质的高尚。事实上，天才作恶具有双倍的危险。
两个诺贝尔奖得主
20世纪初，德国取代英、法成为了世界的科学中心。在当时的德国，科学人才辈出，在物理、化学、数学等各个学科领域都硕果累累。科学的蓬勃兴起影响到了社会和国家的各个方面。在当时的德国有两位在物理学上做出了杰出贡献的人物，一位是勒纳德（Philip Edward Anton Lenard,1862 - 1947），另一位是斯塔克(Johannes Stark,1874-1957)。
勒纳德1862年8月7日出生在捷克的普雷斯布格，曾先后在布达佩斯大学和维也纳大学学习，获得了哲学博士和工程学博士学位。勒纳德是本生的学生，他1883年到德国学习物理，于1892年成为了赫兹研究所的一名研究人员，作赫兹的助手。有一天，赫兹对他说，在阴极射线实验中，用一块铝箔分隔开两个空间，由于铝箔很薄，两个空间之间只有很弱的气压差，便可以观察到阴极射线的传播。赫兹的这一指导使勒纳德解决了阴极射线试验的一个关键问题──用金属箔代替石英板，因而立即发现了阴极射线透射到极前的管外空间中，使放在那里的荧光屏产生了光效应。勒纳德也因此而获得了1905年的诺贝尔物理奖，阴极射线也被称为“勒纳德光”。
斯塔克于1874年4月15日出生在德国的西克肯豪夫。他1898年从慕尼黑大学毕业，在该校物理研究所工作。在1933年 - 1939年任国家物理技术学院院长。斯塔克在物理学的多方面都有贡献。首先他在放电管的研究中取得了重大成果。1908年，他提出了原子的电子模型，认为化学键是由于电子共享引起的。1913年，斯塔克把极隧现象置入一个强电场中，从而在电场中找到了人们长期以来试图寻找的复杂效应：氢原子光谱线的分裂。后来该效应被命名为斯塔克效应。斯塔克由于发现了极隧射线中的多普勒效应和谱线在电场中的分裂，获得了1919年的诺贝尔物理学奖。
不安的年代
当时的德国皇帝威廉二世完全相信科学技术的兴起能够增强国家的实力。因此，他非常乐于为科学领域里大大小小的事情出钱出力。1911年，威廉二世以自己的名字建立了威廉皇帝学会，以后又陆续成立了一系列以威廉皇帝命名的专业学科研究所。在威廉二世对科学倍加关注的表象后面，隐藏着险恶的动机 — 使德国具备称雄欧洲的军事和经济实力。但皇帝的号召力是巨大的，威廉二世的“恩泽”为日后德国科学界掀起民族主义狂潮准备下了一支兴奋剂。
1914年，第一次世界大战爆发。在民族主义精神的驱动下，许多科学家也卷入了这股疯狂的潮流中。1914年10月，包括著名科学家马克思·普朗克、伦琴和奥斯特瓦尔德在内的九十三个科学家、艺术家签名并公布了《文明世界的宣言》。他们谴责英国和法国科学家的剽窃行为，声称许多科学发现是德国科学家首先发现的，只是没有在国外得到承认而已。这个宣言为德国皇帝歌功颂德，为德国的侵略战争进行辩解，宣称全世界人都应该接受“真正德国精神”，是一份不折不扣的沙文主义宣言。
但是，也有少数正直的科学家用理智的眼光面对现实，没有卷进这股逆流中来。其中最引人注目的就是著名的阿尔伯特·爱因斯坦，当时的爱因斯坦由于取得狭义相对论以及光子学说、光电效应、固体比热等多项重大成就，已经是世界知名的大科学家了。由于威廉二世的批准，爱因斯坦于1913年11月12日升任威廉皇帝物理研究所和柏林大学教授。但是皇帝的“恩典”并没有蒙蔽爱因斯坦的眼睛，他不仅拒绝签字，而且毅然参与了反战的《告欧洲人书》的起草工作，并在宣言上签名。尽管最后在这份宣言上签名的只有四个人，并且宣言没有发表，但它表明了爱因斯坦等人发坚定立场和不畏风险的献身精神。
1918年11月9日，在柏林工人和士兵的武装起义面前，威廉二世被迫退位。11月11日，第一次世界大战结束。大战结束后的德国一派沮丧景象。但就在第二年，由著名天文学家爱丁顿率领的一支天文观察队前往北非，对日全食进行观察，验证了爱因斯坦广义相对论的一个推论：光线在强引力场附近发生偏折。这一验证轰动了科学界，使得爱因斯坦和他的理论一下子变得灿烂夺目，因而出现了“相对论热”和“爱因斯坦热”。但是，特殊的时代背景使这种热潮中卷进不少民族主义的东西，经历了战败痛苦的人们，似乎从德国科学家的伟大成就里找到了可以借以安慰的依靠。
向科学开战
勒纳德和斯塔克在最初对爱因斯坦还是抱有好感的。1909年，勒纳德在给爱因斯坦的信中称爱因斯坦是一个有深刻头脑的思想家。斯塔克在1907年曾邀请爱因斯坦在他主持的《电子与辐射年鉴》中写了介绍狭义相对论的文章。斯塔克还曾邀请比他小五岁的爱因斯坦去作他的助教。
但是随着第一次世界大战的爆发的进行，政治立场在科学家之间迅速建立了一道难以逾越的鸿沟。在大战期间勒纳德变成了一个狂热的沙文主义者，他在那份臭名昭著的《文明世界的宣言》中签了名，并且对宣言中的愚蠢准则身体力行。有一次，俄国著名物理学家约飞路过海德堡想要拜访他，竟被他傲慢无理地拒之门外。此外勒纳德还认为，不少英国、法国的科学成果都是剽窃他们德国人的，因此，他要把电流强度的单位由安培（法国人）改成韦伯（德国人）。另外，勒纳德还利用自己的实验室研制军事设备。战争失败又使他迁怒于和平主义者和犹太人，这种情绪燃起了他对爱因斯坦的怒火，竟致终生不灭。他认为爱因斯坦的相对论是英国人吹捧起来的。这种沙文主义的狂热在勒纳德心中不断扩展开来，恶性膨胀，竟致把爱因斯坦的成就视为是自己科学事业的障碍。斯塔克也改变了自己的态度，对爱因斯坦的言行开始怀有一种强烈的憎恶感。
1920年柏林成立了专门攻击爱因斯坦及其相对论的组织“德国自然研究者保持科学纯洁工作小组”。组织的头目是名叫魏兰德。1920年8月6日，魏兰德发表文章攻击相对论。 8月24日，魏兰德在柏林音乐厅精心演出了一幕反相对论的闹剧，爱因斯坦也“应邀”出席。首先发言的魏兰德把爱因斯坦说成是一个抄袭剽窃的人，这种赤裸裸的人身攻击激起了不少人的愤怒。当时在场的德国著名物理学家冯·劳厄对魏兰德的谩骂相当气愤，指责他在丧尽天良的蛊惑人心。
第二天，爱因斯坦被迫还击，在《柏林日报》上发表了题为《我对反相对论公司的答复》的文章，在这篇文章里，爱因斯坦点名批评了勒纳德，并下了要与反对相对论的人士在即将举行的瑙海姆会议上决一胜负的战书。
1920年9月，在法兰克福附近的瑙海姆温泉举行了第八十六届德国自然科学家会议，讨论相对论是会议论题之一。在9月23日那天的辩论中，勒纳德与爱因斯坦的争执还是围绕学术问题进行的。唯恐事态扩大的会议主席普朗克，在长达数小时的辩论之后机智地说，既然相对论还没有做到能使会议可以利用的绝对时间延长，会议只好休会。事后，德国物理学会主席索末菲和玻恩想居间调停这场纷争，但是没有效果，因为争论的根源不在物理学方面，而在政治方面。
其实，早在二十年代初，勒纳德和斯塔克就表示效忠纳粹了。1922年6月，斯塔克在他的《当前德国物理学的危机》一书里，指责相对论有害于德国的实验物理的工作。1924年，还是在希特勒上台之前，当希特勒因政变未遂而被关进监狱里时，斯塔克和勒纳德二人就共同签署了支持希特勒的声明。1930年，斯塔克宣誓加入纳粹。1937年，勒纳德也步其后尘。当爱因斯坦为避开纳粹分子的暗杀阴谋而离德赴美之后，斯塔克还紧追不舍，在《纳粹月刊》上用十分恶毒的语言攻击爱因斯坦，说什么爱因斯坦已经从德国销声匿迹了，整个物理学界再也不会把他的相对论当成神奇的发现了。
1922年10月，为了避开右翼法西斯分子的迫害，爱因斯坦赴日本讲学。11月13日，爱因斯坦从日本讲学完毕，乘船途经上海，瑞典驻上海领事通知爱因斯坦，瑞典科学院决定授予他1921年度的诺贝尔物理奖。授奖原因是由于爱因斯坦的光电效应理论和他在理论物理方面的工作，而没有明说是物理学界公认为最重要成果的相对论，这显然是事出有因的。对此，勒纳德居然穷追不舍，向瑞典科学院递交抗议信。然而，相对论毕竟比诺贝尔奖金更重要，更说明问题。勒纳德为物理学界接受相对论这一事实表示懊丧。这也更加激起了他对爱因斯坦的仇恨。
1931年，希特勒在上台前就声言，即令是象爱因斯坦这样的犹太人，也要从德国滚出去。1933年1月30日，希特勒上台，同年3月，正在美国讲学的爱因斯坦，迫于德国法西斯在国内疯狂迫害进步人士和犹太人这一危难形势，作出了不回德国的决定。这一正义之举更加激怒了右翼分子。1933年3月30日，普鲁士科学院接受了爱因斯坦的辞呈，并多次去信给爱因斯坦，指责爱因斯坦“背叛祖国”的行为。
勒纳德和斯塔克这两位狂热的纳粹分子，肩负着诺贝尔奖获得者的崇高荣誉，在攻击爱因斯坦的高潮中，起到了其他人所不能起到的作用。就在希特勒上台的那一年，勒纳德和斯塔克一左一右地夹击爱因斯坦。勒纳德在纳粹党报《人民观察》上发表攻击爱因斯坦的文章，他恶狠狠地叫喊：“把爱因斯坦这个犹太人当作是一个好德国人是个错误！让相对论在德国存在也是个错误！”与此同时，斯塔克也以国家物理研究所所长的身份咒骂爱因斯坦。
但是，即令当时的德国物理学界，也非纳粹独霸的天下。德国物理学界因为政治态度的尖锐对立而分裂了。1933年9月18日，劳厄作为当时德国物理学会的主席，在物理学年会上作了有名的演讲。他把深受纳粹迫害的爱因斯坦和被宗教裁判所审判的伽利略相提并论。他认为，尽管这些科学伟人都因为追求真理而受到压制，但是，他们都深信：地球仍然在运动！劳厄的发言受到了与会者的欢迎，但却遭到普鲁士教育部的惩戒。
但是，历史不会被无知和强权愚弄。第二次世界大战最后以德国的彻底失败而告终。德国战败两年后，勒纳德死去，斯塔克被德国消灭纳粹主义法院判处徒刑四年。在这场三十年代德国反对相对论的丑恶闹剧里，勒纳德和斯塔克扮演了极其阴险狡诈的角色。他们不是那帮赤裸裸的杀人凶手，也不是戈培尔之流的纳粹宣传喉舌，他们是科学家，而且，他们也不是靠欺骗起家的三、四流科学家，他们是得了世界最高科学荣誉―诺贝尔奖金的第一流科学家。但一流科学家和纳粹精神结合起来给科学所造成的损害，则是别的破坏力量无法替代的，因为天才作恶总是有双倍的危险。
研究文献原文存放：
斯塔克 的讲演稿（Prize Lecture）：
Johannes Stark – Nobel Lecture
Nobel Lecture, June 3, 1920
Structural and Spectral Changes of Chemical Atoms
The question of the composition of perceptible objects is one which already occupied the mind of the ancient Greeks. They formed the concept, as a philosophical speculation, of the indivisible particle, the atom, as the smallest component of perceptible objects. However, they did not pass beyond this stage of the hypothesis; they did not bring it to productivity through experimental research.
It is otherwise with the mind of the Germanic peoples. They proceeded from the experience of their chemical dealings with matter, established the existence of a number of basic substances, or chemical elements, which could not be decomposed further, and proposed the hypothesis that a chemical element consists of homogeneous individuals, or atoms, which are responsible for the peculiar properties of the element, and which with the aid of chemical methods can neither be broken down further nor distinguished from one another.
Towards the end of the last century a certain torpidity fell upon this concept of the chemical atom. Its verification in thousands of chemical experiments led to the belief that the chemical atom not only could not be decomposed into further parts by familiar chemical methods, but that it was completely and absolutely indivisible. Moreover, the abundance of chemical compounds and their importance in daily life hindered the chemist from investigating the question, in what does the individuality of the atoms of different elements consist. In the last three decades the concept of the chemical atom has been set free from this torpidity by our experiences in physics. The discovery of various phenomena has led to a recognition of the fact that the chemical atom is an individual which again is itself made up of several units into a selfcontained whole.
At the head of these new discoveries and insights comes the establishment of the facts that electricity is composed of discrete particles of equal size, or quanta, and that light is an electromagnetic wave motion. It followed necessarily from this that single separate electric quanta must be present in the composition of a chemical atom. For under certain conditions the chemical atoms emit light waves of a specific length or oscillation frequency - their familiar characteristic spectra - and these can come in the form of electromagnetic waves only from accelerated electric quanta.
Moreover, the discovery that the negative electron is a component of the chemical atom is of fundamental importance. In cathode rays the physicist became acquainted with free negative electric quanta capable of independent movement, the mass of which is smaller than a thousandth of the mass of the hydrogen atom. In the process of ionization he saw the liberation of such negative quanta or electrons from the chemical atoms. By exerting the influence of a magnetic field on the spectral lines of chemical elements, Zeeman and Lorentz even succeeded in detecting the negative electron in its place in, and as a component of, the atomic whole.
Furthermore, in these last three decades of great physical discoveries, as never before in history, Nature has drawn back the veil from a third undreamt-of secret before the eyes of the physicist. The discovery and investigation of radioactivity has made clear even for the most sceptical not only the separability of the parts of an atom, but also the chemical and physical individuality of a chemical atom - particularly of a parent atom, but equally of the atoms arising from its decay.
By recognizing that the chemical atom is composed of single separable electric quanta, humanity has taken a great step forward in the investigation of the natural world. However, this advance has faced us with a new, even greater problem - that of the structure of the atom. How many electric quanta are present in the atom of a chemical element? What are their fields of force? What are their mutual distances? What are their movements? What forces are roused on them if their state of equilibrium is disturbed by external interference?
We have been faced with these questions for a decade and a half. It is improbable that speculations will succeed in providing the answer to all these questions at one stroke, by one bold vision. It is more likely that more than a century will pass before we know the structure of the chemical atoms as thoroughly as we do our solar system. The path to this goal will lead, as it has so far, through the difficulties and surprises of experimental research. Many scientists will have to contribute to the solution of the great problem; they will have to follow up and measure all those phenomena in which the atomic structure is directly expressed.
With this in mind, for some twenty years I have set myself as my particular task the experimental investigation of the connexion between change in the structure and change in the spectra of chemical atoms. First of all, two questions may be posed in this connexion.
The first of them is tied up with the phenomenon of change in the structure of the surface of the atom. In order that we may have clearly set out before us every possibility in this respect, we shall proceed from the single atom, the parts of which are all arranged according to mutual equilibrium. We have learnt through experience that when an electrical ray strikes the surface of an atom, an electron, and in some circumstances a second and even a third electron, can be detached. In place of the structure of the neutral atom we are left with the structure of the corresponding monovalent, divalent, or trivalent atomic ion. We ask ourselves: what are the two spectra which belong to the two atomic structures - to neutral atoms and to positive atomic ions? And this question may be supplemented by the second question: is a specific spectrum emitted if the positive atomic ion is changed into a neutral atom?
To these questions I had given certain answers, at first in the form of working hypotheses, after a tentative examination of all previous observation known to me, in order to be able to think out a specific series of experiments to test the hypotheses.
The answer to the first of these questions was as follows: the spectral series of a chemical element are peculiar to the structure of the positive atomic ions, and are observed principally in arcs and sparks, and their lines, as Rydberg showed most successfully, can be grouped together, the lines of each group being a function of the integers.
The second hypothesis was as follows: during the attachment of negative electrons on the positive atomic ions of a chemical element its fine-structure band-spectra are emitted, as in numerous different orbits of attachment the potential energy is emitted in multiples of Planck's quantum constant.
These two working hypotheses have met with very different fates. Not long after its postulation I realized that the second of them was wrong, and neither bore it experimental fruit. However, what has been extraordinarily fruitful theoretically is the nucleus of it - that is, the assumption that energy is emitted in accordance with Planck's quantum law through an electron changing orbits about a positive charge. This assumption forms the startingpoint of Bohr's theory of the emission of serial lines. Although I myself once stood on the threshold of this theory, and although the final formulae give a series of frequency relationships in the spectral series which agree well with observed facts, I am nevertheless unable to believe it, because in its provisions it postulates suppositions which contradict, not only Maxwell's theory, but the very spirit of physics. This criticism is directed not at Planck's quantum of action, but at the hypotheses of Bohr which are bound up with it.
But let us return to the hypothesis that the positive atomic ions are responsible for the spectral series. Shortly after it was formed, I was able to make it bear experimental fruit through the following reflection.
By allowing the positive ions to pass through an electric field and thus giving them a certain velocity, it is possible to distinguish them from the neutral, stationary atoms. If it is possible to deduce their velocity from the spectral lines emitted by them, then this deduction implies the assignment of the displaced spectral lines to the moving atomic ions as emitters. The movement of the emitters of the spectral lines may be deduced on the basis of the Doppler principle.
We can in fact first place the beam of rays of moving positive atomic ions in a plane perpendicular to the axis in which we see the spectral lines emitted by them. These only appear in the places in which they are normally situated in the spectrum when their emitters are stationary. Secondly we can allow the beam of positive atomic ions in our axis of vision to approach us, and then their spectral lines appear to us displaced from their normal place in the spectrum towards the shorter wavelengths, by an amount which is proportional to the velocity of the emitting system. And thirdly, if we make the atomic ions in our axis of vision travel away from us, then their spectral lines appear to us displaced from their normal position towards the opposite side.
In the year 1905 I set about proving experimentally the phenomenon just described. The state of research at that time meant that one had to regard as positive ions the canal rays, which approach the cathode of the glow current and emerge on the other side through perforations in it. I directed the axis of the collimator of my spectrograph first perpendicular to the axis of a beam of hydrogen canal rays, and on a second occasion I allowed the canal rays in the axis of the collimator to approach it. During the comparison of the two spectrograms so obtained, the anticipated Doppler effect in the serial lines of hydrogen appeared, and the same result was later obtained on the serial lines of numerous other chemical elements.
Thus at the beginning of 1906 it seemed to be established that the emitters of the spectral series of chemical elements are their positive atomic ions. This interpretation of my observations, it is true, was soon questioned. For, as particularly W. Wien and J.J. Thomson have shown, canal rays usually contain, beside the positive atomic-ion rays, also neutral rays, so that it was not possible to determine accurately whether the spectral lines showing a Doppler effect should be attributed to the former or the latter. However, cases came to light later in which canal rays containing only positive ions showed a Doppler effect in the spectral lines emitted by them. If even today I still regard the positive atomic ions of a chemical element as the emitters of their spectral series, nevertheless I do not take this concept now as restricted as I did when I only considered free positive atomic ions which owing to their positive total charge are accelerated by the electric field. Rather, in my present opinion, it is possible that the serial lines can in addition be emitted from a positive atomic ion which is not free, and to which a negative electron has already begun to attach itself; only the electron must not yet have come so close to the atomic ion that emission from the latter will already be sensitive to and disturbed by the electric field of the electron.
In this connexion the ultraviolet continuous spectrum of hydrogen may be mentioned. I expected that a continuous spectrum would be emitted when in the course of the attachment of the negative electron to the positive atomic hydrogen ion its encroachment has continued so far that the emission of the serial lines is noticeably disturbed. I therefore looked for - and found - a continuous spectrum in hydrogen canal rays.
Since the discovery of the Doppler effect in canal rays a great number of experiments on this phenomenon have taken place. The following results may, briefly, be deduced from them.
The emitters of the spectral series are without exception single atoms, not compounds of atoms. The spectra of atomic ions of higher valence are different from the spectra of atomic ions of the same element, but of lower valence.
The band-spectra - for example, those of hydrogen and nitrogen - do not as a rule show a canal-ray Doppler effect. Because I expected on the one hand that their emitters were positive molecular ions consisting of more than one atom, and because on the other hand positive molecular ions are also found as canal rays under low pressure, I was led to explain the absence of the Doppler effect in bands by the theory that when stimulation by collision takes place, so that light is emitted, the molecular ions of more than one atom are dissociated after a short period of existence. This concept also makes the canal-ray Doppler effect appear possible in bands, at a small velocity and low pressure. And in fact Mr. Rau of the Würzburg Institute of Physics has recently succeeded in proving this in the case of negative-nitrogen bands. All his observations, moreover, lead to the conclusion that the emitters of these bands are positive diatomic nitrogen molecular ions.
The announcement of this new step forward bids us recognize that research work on the canal-ray Doppler effect is by no means complete and the question of where the various spectra of chemical elements originate has not yet been conclusively answered.
If the experimental physicist has already done a great deal of work in this field, nevertheless the theoretical physicist has still hardly begun to evaluate the experimental material which may lead him to conclusions about the structure of the atom. It has, however, been established that the conversion of the structure of the neutral atom into the structure of the ion involves fundamental changes in the oscillation of the electric quanta which remain in the structure. What conclusions, however, may be drawn from this about the structure of the neutral atom and of the ion remains an unanswered question.
The removal of an electron from the surface of an atom - that is, the ionization of the atom - means a fundamental structural change in its surface layer. That this is accompanied by an equally fundamental change in the spectrum of the surface layer was to be expected from the very first. Matters are different in the case of the second sort of structural change which I made the subject of my experimental research.
We must always bear firmly in mind that the chemical atom is an individual, self-contained structure of positive and negative electric quanta. An external electric field, meeting it and passing through it, affects the negative as much as the positive quanta of the atom, and pushes the former to one side, and the latter in the other direction. Certainly this displacement is soon stopped by the opposing forces which it awakens among the quanta, which are displaced relative to one another, but nevertheless the displacement does take place, and it means a deformation, an alteration of the atomic structure in comparison with its form before the influence of the external electric field. And the question arises whether this sort of alteration of the atomic structure, this deformation by an electric field, manifests itself in an alteration of the spectrum of the atom. In other words, the question of the effect of an electric field on spectral lines has thus arisen.
At the time when I became engaged on this question Voigt had already developed and worked out mathematically a theory of an electric analogue to the Zeeman effect. The result of this theory was not encouraging; because it implied that the alteration to the oscillation frequency, or wavelength, of spectral lines by an electric field would be so small that it would be immeasurable. And this result seemed to be confirmed by the complete absence of success in research to find this effect extending over a number of years.
However, I was unable to accept the presupposition of the theory - namely, the assumption that the emission of a spectral line on the part of an atom was the work of only one single independently moving electron in the atom. In my view the structure of the whole atom was that of an individual, with all its parts interconnected, and the emission of a spectral line appeared to me to be the result of the coherence and co-operation of several electric quanta. Therefore I expected that from the alteration of the atomic structure by an external electric field there would arise also an alteration of the spectrum of the atomic structure. And I tried to solve my problem by producing a strong electric field in a luminous gas. I achieved this by making canal rays, passing through perforations in the cathode, on the other side travel in a strong electric field between the cathode and a second supplementary electrode placed opposite it.
My very first spectrogram of canal rays in hydrogen and helium revealed the effect of the electric field on a number of spectral lines and gave some hint of the wealth of phenomena in the newly opened-up field. Moreover this discovery also showed again how much richer and more original are the works of Nature than the ideas of Man. In the event of the axis on which the observer views the luminous electric field being perpendicular to the axis of the field, the theory had postulated that every single spectral line would be splitted under the influence of the electric field into two components, both of which would appear, relative to the normal line, displaced towards the longer wavelengths, and of which one would vibrate parallel, the other perpendicular, to the field. How different the reality! For example, the red hydrogen line is splitted symmetrically to the normal line into nine components, of which the electric vibrations of six are parallel, and three perpendicular, to the field.
Since the discovery of the effect of an electrical field on spectral lines in the year 1913, already a great number of experiments on it have taken place. The most common and most important result of them is that the nature and size of the effect on corresponding series of different elements are largely an expression of the peculiarity of their atomic structure - or, at least, of the structure of the surface. Thus the effects on the hydrogen series, on the series of mono- and bivalent positive atomic helium ions, on the series of lithium, mercury, and aluminium, differ from one another in characteristic ways.
The following results may be of interest in detail.
Along a series of lines running from longer to shorter wavelengths the effect of the electric field becomes greater as the serial numbers increase - that is, as the wavelength decreases.
The proportion of the intensity of various series within a serial system is, in the case of several elements, dependent on the strength of the deforming electric field. Thus under its influence new series may become visible, which outside the electric field possess so little intensity that they are not observable.
The broadening and displacement of spectral lines which accompanies an increase in the pressure of the gas or in the density of ions, originates in the effect of the electric fields of single atoms on neighbouring light-emitting atoms. Connected with this is Haber's highly promising idea of tracing the heterogeneous catalysis in solid surfaces back to the deformation of the molecular structure by the molecular electric field. Perhaps it will be possible to spectro-analyse accurately such electric fields.
But let us leave these details and return to the problem of the structure of the atom. We must ask ourselves whether a conclusion about the structure of the atom, or at least about the process of the emission of serial lines, may be drawn from the effects of an electric field on serial lines. Now, Bohr and Epstein have developed a theory for the effect in question which gives the number and interval for the component lines in electric fields which agree surprisingly well with observed facts, at least in the case of the series of the monovalent atomic hydrogen ion and of the bivalent atomic helium ion-or, rather, in the case of the electron adhering to these ions. This agreement strongly supports Bohr's theory of the emission of spectral lines, and thus also his presupposition, originating from Rutherford, about the structure of the hydrogen and helium atoms.
In spite of my high estimation of this achievement by the theory, nevertheless I am unable to accept it as definitive; apart from the fact that I am unable to believe in some of its presuppositions, it does not fully correspond to our experience. It cannot explain the following observation, which seems to me very important to research into the structure of the atom.
A beam of luminous hydrogen canal rays has, owing to its velocity, exactly the same direction as that of the electric field in which it may be made to move. If the axis of the beam is placed perpendicular to the axis of the field, the intensities of the components of every single line which is splitted are as symmetrical relative to the normal lint as the intervals at which the components are situated to right and left of it. On the other hand, if the direction of the rays is the same as that of the field, then the intensity of those components which lie on the side towards the longer wavelengths increases. And if the canal rays are made to travel in the opposite direction to that of the field, then vice versa, the components towards the shorter wavelengths appear with greater intensity. It would therefore seem as if a hydrogen atom, or its ion, in an electric field possesses polarity along the axis of the field - that is, two sides may be distinguished in this axis.
This phenomenon is as remarkable as it is important. We may legimately expect to be able to come, from its theoretical implications, to a conclusion about the structure of the hydrogen atom. It may well be successful, if we not only take into account, as has been the case up till now, the effect on a single electron at the surface of the atom, but take as the point of departure for our inferences from the observations the connexion between the parts of an atom which go to make up an individual structure.
Reference to this brings us back to the problem of the structure of the atom. We shall realize the immensity of this problem when we cast a glance behind us at the ground which has already been covered. Research into changes in the spectrum of chemical atoms as a result of changes in their structure has disclosed a whole series of new phenomena. The removal of an electron from the surface of an atom - or its reattachment - leads to fundamental changes in the spectrum of the atomic parts capable of oscillation; and the deformation of the atomic structure by an electric field is expressed by various forms of influence on the oscillation of those atomic parts. But even though these new phenomena have already so richly borne experimental fruit, even though the theories which are beginning to be built on them seem so promising, nevertheless they have hardly begun to clarify the great problem, have only shed light on a small part of the experimental work, and still less on the theoretical field. Research into these phenomena can do no more than contribute a little to the solution of the great problem of the structure of the atom. It will still need the work of many generations to reach that solution. Our advance from the speculative hypothesis of the atom formed by the Greek mind to the discovery of the electric nature of the structure of the atom through the Germanic research of the past century should be an encouragement and a lesson for the century to come.
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