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如果可以放置一圈热的黑咖啡，使光线以一定角度照射在其上，则应该在表面上看到发白的光泽。（与一杯清茶搭配使用，效果会更好。）这种光泽比第一次见到的还要多。它在咖啡表面上形成石板图案，这种较浅颜色的色块与其他色块之间用黑线隔开。斑块通常跨度为一厘米左右。

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这些斑块被科学家称为对流“细胞”，在这些区域中，温暖的流体在上升，而寒冷则在下沉。对流就是天气的全部，更不用说海洋了，您的咖啡也发生了同样的事情。随着表面传感器的浸入和下沉，强迫层从其表面的空气中冷却下来，使其变得温暖，直到表面的咖啡密度降低，但这并非偶然发生或令人困惑。相反，上流和下流的区域将它们自己组织成大小近似相似的列，并排在一起。在咖啡杯中，发白光泽的区域是热咖啡的上升部分，而正是咖啡的热量产生了光泽，尽管用直截了当的方式说出了这一点是错误的：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光泽实际上是一薄层微小的水滴，水滴凝结在咖啡表面上方，并悬停在咖啡表面上方，距离咖啡表面不到一毫米。这是发白的，因为有太多的光从液滴的表面反射。形成水滴是因为当水从液体的高温表面蒸发时会突然冷却，凝结并聚结。形成的水滴不会落回到咖啡分子表面的水分子中，因为它们被咖啡渣吸收了。三人抬高了他们的身体。它们悬浮在表面上方，悬浮在地表之上，是微小的云层，以至于只有细微的光线才能将它们暴露出来。在液滴下方但在液态咖啡上方的微小空间中存在，这将是一次令人难以置信的体验。一件事真是令人发狂，但是你 d还会被表面上散落的东西所搅动，并且一直都在担心滑入下游对流（黑线分隔云层）并消失为下面咖啡的黑度。即使从我们平凡的角度来看（只需低头看着杯子），从一开始就应该清楚地看到水滴在yer绕，您会注意到呼吸瞬间将它们散开，就像风前的乌云一样，但它们又迅速形成。

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唯一可以看到的直达咖啡表面的地方是黑线，就好像您正在透过难以穿透的云层突然破裂看到金星表面一样。凉爽的咖啡沉入那些黑线中，完成对流池的工作。

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逝云或搅动对流室的美丽程度低，但无疑更常见的是咖啡溢出时留下的黑圈。即使是圆环，也为物理学家解决了难题。有趣的是，解决难题后，所涉及的过程与咖啡仍在杯中时所看到的过程相同：石板图案和云层，流体从一个地方到另一个地方的运动以及蒸发。

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?

谜题是这样的：为什么当一滴或半杯咖啡溅出然后变干然后干时，它会形成一个环，而环中几乎所有的黑咖啡原料都几乎空了吗？为什么不干燥并在柜台上留下均匀的米色污点？

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.

这里有一些线索：您可以通过将咖啡倒在天花板上，然后观察干燥来证明它与重力无关。每个单独的液滴仍将在其周围形成黑环。另一方面，它必须与蒸发有关，蒸发是水分子向空气中移动而使固体滞留的过程。芝加哥大学詹姆斯·弗兰克研究所的Sid Nagel及其同事进行了一些早期实验，通过干扰正常的蒸发过程对此进行了测试。在一个容器中，将液滴放在一个很小的玻璃盖下，该玻璃盖在液滴的整个中心上方只有一个小孔。您期望在这些条件下唯一可能的蒸发将是液滴的中心，不是从边缘掉下来在这种特殊情况下，水滴并没有留下任何痕迹。因此，溢出物边缘的蒸发必须与环的形成有关。

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...

在第二个实验中，科学家将滴剂放在了特氟隆上，正如您所知，没有粘到上面。铁氟龙上的水滴也没有留下任何环。在这种情况下，您必须假设铁氟龙的光滑度是关键，这表明形成环的第二个因素是液滴所处的表面。除此之外，如果您使用显微镜观察液滴在干燥过程中的细微行为，您会发现颗粒一直在流向液滴边缘。西德·内格尔（Sid Nagel）形容这就像在纽约看高峰时段。蒸发，表面，流淌这些是您需要了解的内容，才能说明环...

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.

当然，不仅仅是水滴腾出水滴中心的边缘。伴随着一杯咖啡中存在的所有溶解物和颗粒物。它被带走，然后当所有水都蒸发掉时，最终被倒在水滴的边缘。

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.

铁氟龙实验之所以有效，是因为该表面几乎没有不规则性，因此液滴在蒸发时会收缩，并保持其在苦味端的最佳形状。盖实验之所以有效，是因为水不能从液滴的边缘蒸发，只能从中心蒸发，因此不需要液体迁移到边缘，也不需要从中心迁移颗粒物，因此也没有环。在这种情况下，颗粒物只是留在原处，形成污迹。

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饮咖啡，将其吞咽，甚至倒掉，但最重要的是，花一两秒钟检查一下。毕竟，瞥一眼苹果就能激发艾萨克·牛顿的脑海。确实没有很多牛顿，但是早餐桌上的片刻可以提醒我们，我们的生活受到无法控制的力量的影响：诸如表面张力，粘度，蒸发和重力的力量。

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

资料来源：杰伊·英格拉姆（Jay Ingram），“咖啡渍，蜂蜜的速度；以及《日常生活的更多科学》。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-）：加拿大广播公司和新闻记者，以对日常生活科学的热烈欢迎而闻名

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·纳吉尔（Sidney R. Nagel）（1948-）是芝加哥大学的美国科学家和学者，专注于复杂的日常物理学。他的工作包括飞溅液体和液滴形成的高速摄影。

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(微积分) 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

艾萨克·牛顿（Isaac Newton，1642-1727）：英国物理学家和数学家通常被认为是科学史上最原始和最具影响力的理论家之一。除了发明无穷微积分和新的光与色理论外，牛顿还通过他的三个运动定律和万有引力定律改变了物理学的结构。