It's a question that was driving 19th century scientists nuts.

這個問題真的快把 19 世紀的科學家逼瘋了。

Until one of them used an unexpected tool to solve the mystery: a camera.

直到他們其中一人用了讓人意想不到工具才解決這個謎：相機。

Étienne-Jules Marey was an obsessive scientist and inventor who analyzed how things moved.

艾蒂安．朱爾．馬雷對科學及發明很著迷，他喜歡分析物體如何運動。

And he started experimenting with photography at a time when the medium was mostly used to document static subjects.

當大多數的人都還在以靜物作為研究媒介時，他已經開始用攝影來設計實驗了。

But his goal was to capture motion.

他的目標是捕獲那些物體的運動。

And he did that by building on a basic principle of photography: exposing a photosensitive material to light and then covering it in darkness.

他以攝影的基本原則為基礎，先將感光材料曝露在燈光下，再將之罩起。

So his way of creating this darkness and light was to have a disc with slots in it.

為了要製造明暗，他的做法是在圓盤上面挖出狹縫。

By controlling the light as the subject moved across the frame, Marey was able to record movement onto a single glass plate.

當物體在鏡頭前移動時，馬雷藉由控制光線將運動過程記錄在單片玻璃上。

Essentially, all he does is block that light intermittently.

基本上，他做的就是間歇性的阻擋光線。

A slot from the disc opens, and then there's darkness as the man moves, opens, darkness.

光線進入狹縫時會製造出影像，接著人移動時光線便被阻擋，一明一暗不斷交錯。

This technique is called chronophotography, and the results show something human eyes will never see on their own: individual stages of motion.

這種技術叫定時攝影，它可以讓我們看見人眼看不到的東西：物體的個別運動階段。

A couple of years later, Kodak introduced celluloid film and Marey updated his slot camera in a crucial way.

幾年後，柯達採用賽璐珞底片，馬雷隨後也將他的插槽式相機升級，這個轉變十分關鍵。

He swapped the single glass plate with a roll of film that moved in between exposures.

他改用一捲底片代替單片玻璃來曝光。

So, light: an image is made.

有光的時候，就會顯現影像。

Darkness, the film moves on.

暗的時候底片就會轉動。

Light, an image — so it's a movie camera, is what it is.

有光又出現影像，這就是電影照相機。

Marey made a lot of films for research purposes.

為了研究，馬雷拍攝了許多影片。

And even tried dropping other animals to see if they'd land on their feet, specifically this rabbit and this chicken.

甚至嘗試讓其它動物落下，看他們能不能以腳著地，像是這隻兔子和這隻雞。

Which brings us back to the cat.

這也讓我們的主題回到貓咪。

It seems to be able to right itself by flipping in the air without pushing off anything first, which would contradict the law of conservation of angular momentum.

貓咪似乎可以不用對任何東西施力就在空中翻轉身體，但這樣會跟角動量守恆定律相衝突。

Sounds scary, but stick with me here.

聽起來有點可怕，但請繼續聽我解釋。

One of Newton's laws of motion says that something in motion can't just stop itself unless an opposing force acts upon it.

其中一個牛頓運動定律說到：一個移動中的物體無法自己停下來，除非有反方向的力作用於他身上。

Basically, you can't just change direction midair, Wile E. Coyote style.

基本上你不能像威利狼與嗶嗶鳥一樣在半空中改變方向。

But to the naked eye, it looks like a cat can.

但就肉眼看來，貓咪好像就是可以做到。

Most people assumed the cat was "cheating" by kicking off the hands of the person dropping it.

多數人認為貓咪是用腳蹬人的手來做弊的。

But Marey's film showed what's actually happening.

馬雷的影像說明了這段過程中到底發生什麼事。

The first few frames prove right away that the cat doesn't start its rotation from a kick.

前面幾幀照片就證實了，貓咪一開始並沒有用踢的方式來旋轉方向。

But what it does do is arch its back.

但牠弓起了牠的背部。

And by arching its back, it's divided its body into a front part and a back part, and the two parts can work independently.

弓起背部後，牠將身體分為前半部與後半部，這兩部分可以分開來活動。

You know how a figure skater pulls their arms in to rotate faster?

你知道花式滑冰員是如何藉由收攏雙臂來越轉越快的嗎？

That's whats happening here, too.

貓咪旋轉的原理也是這樣。

Early in the rotation, the cat pulls its front legs in and leaves the back splayed out.

剛開始旋轉時，貓咪會將前腳收起，背部維持伸展的樣子。

So the front half can rotate quickly while the back half stays relatively still.

所以牠的前半部就可以快速轉動，而後半部可以保持靜止。

Then halfway through, it does the opposite.

要轉動身體後半部時則相反。

Front legs stretched out, back ones tucked in to flip the other half of its body around.

牠會將前腳身直、後腳縮起來，好讓後半部的身體轉向。

And you notice by the time the cat is landing, all four legs are stretched out as far as they can be, which means slow rotation.

你會注意到當貓咪落地時，牠們的四隻腳會盡可能地伸直，讓身體能夠轉得較慢。

So the cat has rotated itself, but not overall; the two halves are working in opposite ways.

所以貓咪的確可以靠自己在空中旋轉，但是是將身體分成兩半部，以相反方向來運作。

It uses the inertia of its own bodyweight to spin each side.

牠利用自身體重的慣性來旋轉。

And because the two spins operate separately in opposing directions, they cancel each other out.

因為前、後半部的旋轉方向恰恰相反，因此兩個力就可以互相抵銷。

So Newton's law isn't broken.

所以牛頓的定律並沒有被打破。

Marey published his findings in Nature in 1894, breaking down the falling cat problem for the first time.

馬雷將牠的發現刊登在 1894 年的《自然》期刊上，第一次解開了「為何貓咪可以穩穩落地」的問題。

His work remains an early example of using photography for scientific discovery.

他的這項成果便是早期運用攝影來挖掘科學真相的實例。

What does photography do for science?

攝影技術對科學做出了什麼貢獻呢？

It records something and it makes it permanent so you can analyze it later, or so you can share it.

它可以記錄下某件事，讓那一刻永久保存，所以我們就可以加以分析或分享給別人。

But what Marey did was show something that the eye could not possibly see — ever.

但馬雷所做出的貢獻是讓我們看見人眼永遠無法看見的事物。

You might have seen another famous early example of motion photography.

你可能看過早期另一個很有名的例子，也是拍攝物體的運動。

In 1878, Eadweard Muybridge used 12 cameras connected to tripwires to prove that a horse lifts all four feet off the ground at some point in a gallop.

1878 年，埃德沃德．邁布里奇用導線將 12 台相機連接在一起，最後證明馬隻有時在急速奔馳時會四蹄騰空。