How does the tiny ball in a pen deliver ink to paper?
笔尖的小球，怎样把墨水送到纸上？
拿圆珠笔写字时，真正接触纸面的，是笔尖上一颗很小的球。
When you write with a ballpoint pen, the part that actually touches the paper is a tiny ball at the tip.
这颗球既不能掉出来，也不能被固定得一动不动。
The ball must neither fall out nor be held so tightly that it cannot move.
它被装在一个小座里，位置受到限制，却仍能自由转动。
It sits in a small socket that holds it in place while still allowing it to rotate freely.
笔芯里的墨水到达球的内侧，球随着笔在纸上移动而滚动，把墨水带到纸面。
Ink from the reservoir reaches the inner side of the ball, which rolls as the pen moves across the paper and carries ink onto the surface.
所以，笔尖不只是让墨水流出的一个小孔，球的转动也是供墨过程的一部分。
The tip is therefore more than a small hole for ink to flow through: the ball’s rotation is part of the ink-delivery process.
不过，把球装进去还不够，墨水必须有路可走。
Fitting the ball is not enough, though: the ink must have a path to follow.
美国机械工程师学会的一份技术史资料，记录了比罗改进笔尖时遇到的问题。
A technical history document from ASME, the American Society of Mechanical Engineers, records a problem Bíró encountered while improving the tip.
早期试验中，书写压力会把球压在底座上，阻碍墨水流动。
In early trials, writing pressure pushed the ball against its seat and obstructed the ink flow.
后来增加的小槽，让墨水能够经过球与底座接触的地方，继续到达笔尖。
Small grooves added later allowed ink to pass through the area where the ball met its seat and keep reaching the tip.
一条看似简单的笔画，背后其实有滚动的小球，也有为墨水留下的通道。
Behind a seemingly simple pen stroke are both a rolling ball and a passage left open for the ink.
