萬物簡史 第68期:事物的測定(26)

Delicacy was the key word. Not a whisper ofdisturbance could be allowed into the roomcontaining the apparatus, so Cavendish took up aposition in an adjoining room and made hisobservations with a telescope aimed through apeephole. The work was incredibly exacting andinvolved seventeen delicate, interconnectedmeasurements, which together took nearly a year tocomplete. When at last he had finished hiscalculations, Cavendish announced that the Earthweighed a little over six billion trillion metric tons, touse the modern measure. (A metric ton is 1,000 kilograms or 2,205 pounds.)

精密是個關(guān)鍵詞。設備所在的屋子里，容不得半點兒干擾。因此，卡文迪許就待在旁邊的一間屋里，用望遠鏡瞄準一個窺孔來進行觀察。這項工作是極其費勁的，要做17次精密而又互不關(guān)聯(lián)的測量，他總共花了將近一年時間才完成。卡文迪許終于計算完畢，宣布地球的重量略略超過6 000 000 000 000 000 000 000噸(1噸約等于2205磅)。

Today, scientists have at their disposal machines so precise they can detect the weight of asingle bacterium and so sensitive that readings can be disturbed by someone yawningseventy-five feet away, but they have not significantly improved on Cavendish's measurementsof 1797. The current best estimate for Earth's weight is 5.9725 billion trillion metric tons, adifference of only about 1 percent from Cavendish's finding. Interestingly, all of this merelyconfirmed estimates made by Newton 110 years before Cavendish without any experimentalevidence at all.

今天科學家手里的儀器，其精確度之高，可以測定一個細菌的重量;其靈敏度之高，有人在25米以外打個呵欠都會干擾讀數(shù)。但是，他們對卡文迪許1797年的測量結(jié)果沒有重大改動。目前對地球重量的最準確估計數(shù)是59725億億噸，與卡文迪許的結(jié)果只相差1%左右。有意思的是，這一切都只是證實了在卡文迪許110年之前牛頓的估計，而且沒有跡象表明牛頓做過任何試驗。

So, by the late eighteenth century scientists knew very precisely the shape and dimensions ofthe Earth and its distance from the Sun and planets; and now Cavendish, without even leavinghome, had given them its weight. So you might think that determining the age of the Earthwould be relatively straightforward. After all, the necessary materials were literally at theirfeet. But no. Human beings would split the atom and invent television, nylon, and instantcoffee before they could figure out the age of their own planet.

無論如何，到18世紀末，科學家們已經(jīng)知道地球的確切形狀和大小，以及地球到太陽和各個行星的距離。連足不出戶的卡文迪許都已算出了它們的重量。于是，你或許會認為，確定地球的年齡會是一件相對容易的事。畢竟，他們實際上已經(jīng)掌握一切必要的資料。然而，實際情形并非如此。人類要等到能夠分裂原子、發(fā)明電視、尼龍和速溶咖啡以后，才算得出我們自己這顆行星的年齡。

To understand why, we must travel north to Scotland and begin with a brilliant and genialman, of whom few have ever heard, who had just invented a new science called geology.

若要知道其中的原因，我們必須北上去一趟蘇格蘭，先去拜訪一位杰出而又可親的人。這個人很少有人聽說過，他剛剛發(fā)明了一門新學科：地質(zhì)學。