SSS 2011-01-24
时间：2018-12-24 作者：英语课 分类：Scientific American(一)月
This is Scientific American's 60-Second Science. I'm John Matson. Got a minute?
In a laboratory vault 1 outside Paris is a small cylinder 2 of platinum–iridium alloy 3 that serves as the standard for all mass measurements worldwide. By an 1889 international accord, the mass of this metal cylinder defines the kilogram.
But that may soon change. The kilogram is the only unit of measurement still based on a man-made artifact. A second of time, for instance, is now defined in terms of an electron transition of the cesium atom. And the meter is tied to the speed of light. Those standards are universal and unchanging—unlike the official kilogram. The reference cylinder's mass has drifted slightly through the years—not enough to throw off your bathroom scale, but enough to bother measurement scientists.
Some of them are meeting January 24th at the Royal Society in London to discuss future improvements to the measurement units. The plan is to eventually relate the kilogram to a universal number known as Planck's constant. But the technology needed to do that is not yet fully 4 developed. So, for the time being, that little metal cylinder will just have to keep pulling its weight. I mean, mass.
Thanks for the minute. For Scientific American's 60-Second Science, I'm John Matson.
- The vault of this cathedral is very high.这座天主教堂的拱顶非常高。
- The old patrician was buried in the family vault.这位老贵族埋在家族的墓地里。
- What's the volume of this cylinder?这个圆筒的体积有多少？
- The cylinder is getting too much gas and not enough air.汽缸里汽油太多而空气不足。