物理學 1895

論一種新型的射線

威廉·康拉德·倫琴

一種看不見的射線，穿過血肉、被骨頭擋下，把體內的骨架照了出來。

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In depth · the introduction

1895 年冬天，一位德國物理學家注意到一抹他無法解釋的微光——而短短數週之內，全世界就能看見一隻活人手裡的骨頭。

把這個想法拆開看

倫琴發現了一種看不見的射線：它從一隻通了電的真空管裡湧出，能徑直穿過紙張、木頭與身體的柔軟部分。越緻密的東西越能攔住它；骨頭吸收的，遠比血肉多，而鉛之類的金屬，幾乎能把它完全擋下。

把這些射線對準一隻放在發光屏（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，便在血肉那淡淡的輪廓裡清晰地顯現出來。這是歷史上頭一回，人們不必動刀，就能看進一具活著的身體。

它從哪裡來

1895 年 11 月 8 日，倫琴獨自在維爾茨堡的實驗室裡，把一隻放電管嚴嚴實實裹進黑色硬紙板，房間也是全黑的——可將近一公尺外的一塊屏，卻閃起了微光。任何普通的光，都不可能逃出那層遮擋。他被牢牢攫住，接下來的七個星期裡幾乎沒離開過實驗室，據說就在那裡吃、在那裡睡，一樣樣去試：這射線，能穿過什麼，又穿不過什麼。

12 月 22 日，他拍下了妻子安娜·貝爾塔的手；據說，看見自己的骨架與結婚戒指，她說：「我看見了我的死亡。」12 月 28 日，他遞交了那篇簡短的報告；到了 1 月，這個消息——連同那張詭異的影像——已傳遍了世界。

它為何重要

短短幾個月，醫學被改寫了。醫生們不必再做探查性的手術，就能定位骨折、子彈與誤吞之物；頭一年裡，X 射線就到了戰地醫院。由於倫琴說不出這射線究竟是什麼，他便借用數學裡那個表示「未知」的符號，叫它 X。他還拒絕為這一發現申請專利，認為它屬於每一個人——後來更把諾貝爾獎的獎金捐了出去。

一個可以拿來想像的畫面

想想夜裡的霧。汽車的大燈能穿過薄霧，卻被濃霧吞沒。X 射線做的是更戲劇化的那一版：血肉像薄霧，讓大部分射線穿過；骨頭像濃霧，擋下的多得多；而一片鉛，就像一堵實牆。你在屏上看到的影子，不過是一張地圖——它標出你身體的每一處，分別是多濃的「霧」。

它落在何處

倫琴的射線，揭開了一陣非凡的發現熱潮。它促使亨利·貝克勒爾去尋找相關的效應，並在 1896 年意外撞見了放射性；這又把瑪麗與皮埃爾·居禮引向了 1898 年的鐳（本館也講了那個故事）。這射線究竟是什麼，一直成謎，直到 1912 年——它被一塊晶體衍射，證明原來是波長極短的光；而正是這同一種衍射，後來成了揭示 DNA 結構的那件工具。

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