物理学 1895

论一种新型的射线

威廉·康拉德·伦琴

一种看不见的射线，穿过血肉、被骨头挡下，把体内的骨架照了出来。

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In depth · the introduction

1895 年冬天，一位德国物理学家注意到一抹他无法解释的微光——而短短数周之内，全世界就能看见一只活人手里的骨头。

把这个想法拆开看

伦琴发现了一种看不见的射线：它从一只通了电的真空管里涌出，能径直穿过纸张、木头与身体的柔软部分。越致密的东西越能拦住它；骨头吸收的，远比血肉多，而铅之类的金属，几乎能把它完全挡下。

把这些射线对准一只放在发光屏（或照相底片）前的手，吸收得最多的部位，就投下最深的影子。骨骼，便在血肉那淡淡的轮廓里清晰地显现出来。这是历史上头一回，人们不必动刀，就能看进一具活着的身体。

它从哪里来

1895 年 11 月 8 日，伦琴独自在维尔茨堡的实验室里，把一只放电管严严实实裹进黑色硬纸板，房间也是全黑的——可将近一米外的一块屏，却闪起了微光。任何普通的光，都不可能逃出那层遮挡。他被牢牢攫住，接下来的七个星期里几乎没离开过实验室，据说就在那里吃、在那里睡，一样样去试：这射线，能穿过什么，又穿不过什么。

12 月 22 日，他拍下了妻子安娜·贝尔塔的手；据说，看见自己的骨架与结婚戒指，她说：「我看见了我的死亡。」12 月 28 日，他递交了那篇简短的报告；到了 1 月，这个消息——连同那张诡异的影像——已传遍了世界。

它为何重要

短短几个月，医学被改写了。医生们不必再做探查性的手术，就能定位骨折、子弹与误吞之物；头一年里，X 射线就到了战地医院。由于伦琴说不出这射线究竟是什么，他便借用数学里那个表示「未知」的符号，叫它 X。他还拒绝为这一发现申请专利，认为它属于每一个人——后来更把诺贝尔奖的奖金捐了出去。

一个可以拿来想象的画面

想想夜里的雾。汽车的大灯能穿过薄雾，却被浓雾吞没。X 射线做的是更戏剧化的那一版：血肉像薄雾，让大部分射线穿过；骨头像浓雾，挡下的多得多；而一片铅，就像一堵实墙。你在屏上看到的影子，不过是一张地图——它标出你身体的每一处，分别是多浓的「雾」。

它落在何处

伦琴的射线，揭开了一阵非凡的发现热潮。它促使亨利·贝克勒尔去寻找相关的效应，并在 1896 年意外撞见了放射性；这又把玛丽与皮埃尔·居里引向了 1898 年的镭（本馆也讲了那个故事）。这射线究竟是什么，一直成谜，直到 1912 年——它被一块晶体衍射，证明原来是波长极短的光；而正是这同一种衍射，后来成了揭示 DNA 结构的那件工具。

The original document

Original source text

W. C. Röntgen · "Über eine neue Art von Strahlen" · Würzburg Physico-Medical Society, 28 Dec 1895 · transl. A. Stanton, Nature 53 (1896)

The observation

A discharge from a large induction coil is passed through a Hittorf's vacuum tube, or through a well-exhausted Crookes' or Lenard's tube. The tube is surrounded by a fairly close-fitting shield of black paper; it is then possible to see, in a completely darkened room, that paper covered on one side with barium platino-cyanide lights up with brilliant fluorescence when brought into the neighbourhood of the tube.

The black shield is opaque to all visible and ultraviolet light, yet the screen still glows — so something else is crossing the room. Röntgen finds that this agent passes through books, wood, thin metals and the soft tissues of the body, the opacity rising with the thickness and density of what it meets, and that it darkens a photographic plate.

Naming the rays

For brevity's sake I shall use the expression 'rays'; and to distinguish them from others of this name I shall call them 'X-rays.'

He could not determine their nature, hence the algebraic 'X'. He reports that they travel in straight lines and cast sharp shadows, that they are not regularly reflected or refracted as ordinary light is, and — decisively — that they are not deflected by a magnet, which sets them apart from the cathode rays inside the tube.

The shadow of the bones

If the hand be held before the fluorescent screen, the shadow shows the bones darkly, with only faint outlines of the surrounding tissues.

Six days before submitting the paper, on 22 December 1895, he had recorded his wife Anna Bertha's hand on a photographic plate — the bones and her ring standing out within the faint shadow of the flesh, the first radiograph of a human body.

[ … ]

The full preliminary communication catalogues the transparency of many materials, the discharging of electrified bodies, and the failure of prisms, lenses and magnets to bend the rays — and closes by leaving their physical nature an open question. Read it in full at the source below.

Würzburg · 28 December 1895