1If you can position a cyp of hot, black coffee so that light strikes it at an angle, you should see a whitish sheem on the surface. (This works even better with a cup of clear tea.)There's something more to this sheen than first meets the eye. It makes a flagstone pattern on the surface of the coffee, with patches of this lighter color separated from other patches by dark lines. The patches are usually a centimeter or so across.

1如果可以放置一圈熱的黑咖啡，使光線以一定角度照射在其上，則應該在表面上看到發白的光澤。（與一杯清茶搭配使用，效果會更好。）這種光澤比第一次見到的還要多。它在咖啡表面上形成石板圖案，這種較淺顏色的色塊與其他色塊之間用黑線隔開。斑塊通常跨度為一厘米左右。

2 These patches are what scientists call convection "cells,"areas where warm fluid is rising and cold is sinking. Convection is what the weather is all about, not to mention ocean cufrents, and the same thing in miniature happens in your coffee. As the surface enser and sinks, forcing layer cools from cohtact with the air above it, it becomes d warmer, less dense coffee up to the surface But this doesn't happen in a haphazard hoep or confusing way. Rather, the areas of upliow and downflow organize themselves into roughly similar sized columns, gne beside the other. In the coffee cup the areas with the whitish sheen are rising coltmns of hot coffee, and it's the heat of that coffee that creates the sheen, although saying it in that straightforward way misses the point: A drana is being played out at the surface of the coffee.

2這些斑塊被科學家稱為對流“細胞”，在這些區域中，溫暖的流體在上升，而寒冷則在下沉。對流就是天氣的全部，更不用說海洋了，您的咖啡也發生了同樣的事情。隨著表面傳感器的浸入和下沉，強迫層從其表面的空氣中冷卻下來，使其變得溫暖，直到表面的咖啡密度降低，但這并非偶然發生或令人困惑。相反，上流和下流的區域將它們自己組織成大小近似相似的列，并排在一起。在咖啡杯中，發白光澤的區域是熱咖啡的上升部分，而正是咖啡的熱量產生了光澤，盡管用直截了當的方式說出了這一點是錯誤的：咖啡。

3 The sheen is actually a thin layer of tiny water dro plets, droplets that have condensed just above the surface of the coffee and are hovering there, less than a millimeter above the surface. It's whitish because so much light reflects from the surfaces of the droplets. The droplets form because as the water evaporates from the hot surface of the liquid, it cools suddenly, condenses and coalesces.The drops that form do not fall back ohto the Iohns of water mofecules still surface of the coffee because they are bueyed up by the tri rising up underheath them. Held there, suspended above the surface, they are clouds on a scale so minute that only careful lighting reveals them. It would be an incredible experience to be there in the tiny space under the droplets but above the liquid coffee. It would be hellishly hot for one thing, but you'd also be buffeted by stuff evaperating from the surface, and concerned all the while about slipping into the downstream convection (the black lines separating the clouds)and vanishing into the blackness of the coffee below. Even from our mundane perspective(simply looking down on the cup)it should have been apparent from the start that the drops were hoyering you would have noticed that a breath scatters them instantly, like clouds before the wind, but they form again just as quickly.

3光澤實際上是一薄層微小的水滴，水滴凝結在咖啡表面上方，并懸停在咖啡表面上方，距離咖啡表面不到一毫米。這是發白的，因為有太多的光從液滴的表面反射。形成水滴是因為當水從液體的高溫表面蒸發時會突然冷卻，凝結并聚結。形成的水滴不會落回到咖啡分子表面的水分子中，因為它們被咖啡渣吸收了。三人抬高了他們的身體。它們懸浮在表面上方，懸浮在地表之上，是微小的云層，以至于只有細微的光線才能將它們暴露出來。在液滴下方但在液態咖啡上方的微小空間中存在，這將是一次令人難以置信的體驗。一件事真是令人發狂，但是你 d還會被表面上散落的東西所攪動，并且一直都在擔心滑入下游對流（黑線分隔云層）并消失為下面咖啡的黑度。即使從我們平凡的角度來看（只需低頭看著杯子），從一開始就應該清楚地看到水滴在yer繞，您會注意到呼吸瞬間將它們散開，就像風前的烏云一樣，但它們又迅速形成。

4 The only place where you can see right down to the coffee surface is along the black lines, as if you are seeing the surface of Venus through a sudden break in its impenetrable clouds. The cool coffee sinks in those black lines, completing the convection cell...

4唯一可以看到的直達咖啡表面的地方是黑線，就好像您正在透過難以穿透的云層突然破裂看到金星表面一樣。涼爽的咖啡沉入那些黑線中，完成對流池的工作。

5 Less beauteous than evanescent clouds or churning convection cells, but certainly more common, is the dark ring left behind when coffee spills. Even the ring presented a puzzle for physicists to solve. Funnily enough, when the puzzle was solved, the processes involved turned out to be the same as seen in coffee when it was still in the cup: the flagstone pattern and the clouds, the movement of fluid from one place to another, and evaporation.

比e逝云或攪動對流室的美麗程度低，但無疑更常見的是咖啡溢出時留下的黑圈。即使是圓環，也為物理學家解決了難題。有趣的是，解決難題后，所涉及的過程與咖啡仍在杯中時所看到的過程相同：石板圖案和云層，流體從一個地方到另一個地方的運動以及蒸發。

6 The puzzle is this: Why, when a drop, or half cup of coffee spills and then dries, does it form a ring, with almost all of the dark coffee stuff in the ring and the center almost empty? Why shouldn't it dry and leave a uniform beige stain on the counter?

謎題是這樣的：為什么當一滴或半杯咖啡濺出然后變干然后干時，它會形成一個環，而環中幾乎所有的黑咖啡原料都幾乎空了嗎？為什么不干燥并在柜臺上留下均勻的米色污點？

7 Here are some clues: You can show that it doesn't have anything to do with gravity by throwing your cup of coffee onto the ceiling, then watching as it dries. Each individual drop will still form dark ring at its perimeter. On the other hand, it must have something to do with evaporation, the process by which the water molecules move into the air, leaving the solids behind. A couple of early experiments by Sid Nagel and his colleagues at the James Franck Institute at the University of Chicago tested this by interfering with the normal evaporative process. In one, drop was placed under a tiny glass lid that had only a minute hole over the very center of the drop. You would expect under these conditions that the only evaporation possible would be from the center of the drop, not from the edge In this special circumstance drops did not leave a ring behind. So evaporation from the edge of the spill must have something to do with the formation of the ring.

這里有一些線索：您可以通過將咖啡倒在天花板上，然后觀察干燥來證明它與重力無關。每個單獨的液滴仍將在其周圍形成黑環。另一方面，它必須與蒸發有關，蒸發是水分子向空氣中移動而使固體滯留的過程。芝加哥大學詹姆斯·弗蘭克研究所的Sid Nagel及其同事進行了一些早期實驗，通過干擾正常的蒸發過程對此進行了測試。在一個容器中，將液滴放在一個很小的玻璃蓋下，該玻璃蓋在液滴的整個中心上方只有一個小孔。您期望在這些條件下唯一可能的蒸發將是液滴的中心，不是從邊緣掉下來在這種特殊情況下，水滴并沒有留下任何痕跡。因此，溢出物邊緣的蒸發必須與環的形成有關。

8 In a second experiment the scientists placed drops on Teflon, to which, as you know, nothing sticks. Drops left on Teflon didn't leave a ring either. In this case you'd have to suppose that the smoothness of Teflon would be the key, suggesting that a second factor in ring formation is the surface on which the drop is sitting. Add to these the fact that if you use a microscope to watch the behavior of tiny particles in the drop as it is drying, youll see that the particles are streaming headlong out to the edge of the drop. Sid Nagel described it as being like watching rush hour in New York. Evaporatio, the surface, the streaming those are the things you need to know to be able to account for the ring...

在第二個實驗中，科學家將滴劑放在了特氟隆上，正如您所知，沒有粘到上面。鐵氟龍上的水滴也沒有留下任何環。在這種情況下，您必須假設鐵氟龍的光滑度是關鍵，這表明形成環的第二個因素是液滴所處的表面。除此之外，如果您使用顯微鏡觀察液滴在干燥過程中的細微行為，您會發現顆粒一直在流向液滴邊緣。西德·內格爾（Sid Nagel）形容這就像在紐約看高峰時段。蒸發，表面，流淌這些是您需要了解的內容，才能說明環...

9 Of course, it's not just the water that vacates the center of the drop for the edges. With it goes all the dissolved and particulate matter that exists in a cup of coffee. It is carried along, then finally dumped at the edge of the drop when all the water has evaporated.

當然，不僅僅是水滴騰出水滴中心的邊緣。伴隨著一杯咖啡中存在的所有溶解物和顆粒物。它被帶走，然后當所有水都蒸發掉時，最終被倒在水滴的邊緣。

10 The Teflon experiment worked because the surface is virtually free of irregularities, so the drop can contract as it evaporates, maintaining its preferred shape to the bitter end. The lid experiment worked because the water could not evaporate from the edges of the drop, only from the center, so there was no need for the liquid to migrate out to the edges, no transport of particulate matter from the center and therefore no ring. In that case the particulate matter was simply left where it was, forming a smudge.

鐵氟龍實驗之所以有效，是因為該表面幾乎沒有不規則性，因此液滴在蒸發時會收縮，并保持其在苦味端的最佳形狀。蓋實驗之所以有效，是因為水不能從液滴的邊緣蒸發，只能從中心蒸發，因此不需要液體遷移到邊緣，也不需要從中心遷移顆粒物，因此也沒有環。在這種情況下，顆粒物只是留在原處，形成污跡。

11 Sip your coffee, gulp it, even spill it, but above all, take a second or two to check it out. After all, a glance at an apple stimulated great thoughts in Isaac Newton's head. It's true there aren't very many Newtons, but a few moments at the breakfast table can serve as reminder that yes, our lives are under the influence of forces beyond our control: forces like surface tension, viscosity, evaporation, and gravity.

coffee飲咖啡，將其吞咽，甚至倒掉，但最重要的是，花一兩秒鐘檢查一下。畢竟，瞥一眼蘋果就能激發艾薩克·牛頓的腦海。確實沒有很多牛頓，但是早餐桌上的片刻可以提醒我們，我們的生活受到無法控制的力量的影響：諸如表面張力，粘度，蒸發和重力的力量。

Source: Jay Ingram, "Coffee stains, The Velocity of Honey; and More Science of Everyday Life. Aurum Press, 2004.

資料來源：杰伊·英格拉姆（Jay Ingram），“咖啡漬，蜂蜜的速度；以及《日常生活的更多科學》。Aurum出版社，2004年。

NOTES

Jay Ingram(1945-): Canadian broadcaster and journalist, known for his enthusiastic popularization of the science of everyday life

杰伊·英格拉姆（Jay Ingram）（1945-）：加拿大廣播公司和新聞記者，以對日常生活科學的熱烈歡迎而聞名

Sid Nagel (Sidney R. Nagel)(1948-) American scientist and academic based at the University of Chicago, focusing on complex everyday physics. His work includes high-speed photography of splashing liquids and drop formation.

席德·納吉爾（Sidney R. Nagel）（1948-）是芝加哥大學的美國科學家和學者，專注于復雜的日常物理學。他的工作包括飛濺液體和液滴形成的高速攝影。

Isaac Newton(1642-1727): English physicist and mathematician generally regarded as one of the most original and influential theorists in the history of science. In addition to his invention of the infinitesimal calculus(微積分) and new theory of light and color, Newton transformed the structure of physical science with his three laws of motion and the law of universal gravitation

艾薩克·牛頓（Isaac Newton，1642-1727）：英國物理學家和數學家通常被認為是科學史上最原始和最具影響力的理論家之一。除了發明無窮微積分和新的光與色理論外，牛頓還通過他的三個運動定律和萬有引力定律改變了物理學的結構。