第3章　地球的內部

還在很小的時候，我就很喜歡打破砂鍋問到底。至少來說，我的奶媽是這樣認為的。

有一天，我正跟著她沿著市里的人行道散步，我問她說：

“簡，人行道下面是什么？”

“哦，全都是土啊。”她回答道。

“土下面又是什么呢？”

“哦，還是土。”她回答道。

“好吧，那下面又是什么呢？”我問道。她的回答可沒有讓我覺得滿意。

“噢，沒有什么了吧，我可不知道。你為什么總是這樣喜歡刨根問底呢？”她問道。

我知道，泥土下面肯定是有某種東西的，我就是想知道，那種東西究竟是什么，誰叫我喜歡刨根究底呢。

我曾經聽說，壞孩子死后，會去地下的某個地方，或許是一個大洞穴吧，因此，我希望弄明白，究竟是不是那么回事。

于是，我便下定決心，要向下挖穿整個地球，并且一直向下、向下、向下挖掘，直到我抵達地球的那一邊，那樣一來，我就知道情況究竟是不是那樣的了。你們都知道，當時我還是個很小很小的小男孩哩。我拿起一把錫制的鏟子，開始在我家后院的葡萄架后挖出一個洞來。在那里進行挖掘，就沒人知道我在干什么。我希

after day I worked, digging up first soft ground—that was easy—then I got down to solid ground；that was hard. I had a hole which I could stand in up to my waist.

Then one evening my father asked，“What's that hole in the back yard?”

My secret was out. He didn't laugh when I told him—at least, out loud—but he asked me if I knew how far I'd have to dig.

“Could you dig down as deep as the Washington Monument goes up?”he asked.

I thought perhaps I could, but I was a little doubtful, for the Washington Monument seemed terribly high.

“Men have dug wells many times as deep as the Washington Monument，”my father told me，“but never all the way nor nearly all the way through the World. You would have to dig many thousands of times deeper than the Washington Monument to get down even to the center of the World.It's eight thousand miles straight through the earth and most all the way is rock—just rock, and more rock, that's all.”

Then I gave it up.

“How do you know it's eight thousand miles if no one has ever been through the World?”asked the inquisitive

望在一路挖通之前，保守住這個秘密。我干了一天又一天，起初挖出的都是松軟的泥土，很容易挖掘；可接下來，我就挖到結實的土層，很難挖下去了。我挖出了一個洞，站在里面，洞子只有我的腰部那么深。

然后，有天傍晚，我的父親問道：“后院里那個洞是干什么用的？”

我的秘密便公之于眾了。我把這一切告訴父親時，他并沒有笑起來（起碼也是沒有哈哈大笑），而是問我，知不知道自己必須挖多遠才能挖穿。

“你向下挖掘出的深度，能夠達到華盛頓紀念碑向上聳立的那種高度嗎？”他問道。

雖然覺得自己可能做得到，但我還是有一點兒懷疑，因為華盛頓紀念碑看上去，可高得很呢。

“人類向下挖掘的深度，已經達到華盛頓紀念碑高度的好多、好多倍了，”父親告訴我說，“可從來沒有挖穿過，或者接近挖穿過地球呢。你必須挖到有華盛頓紀念碑高度的幾千倍深，才能挖到地心。地球的直徑有八千英里，而且其中絕大部分都是巖石，全都是巖石，好多好多的巖石，沒有其他的東西。”

于是，我便不再挖下去了。

“如果說到現在為止，還沒有人挖穿過整個地球，那您又怎么知道地球的直徑是八千英里呢？”那個喜歡刨根問底的孩子問道。我不記得父親當時是怎樣回答我

child. I don't know what my father answered.I was too young to understand.I wonder if you are too young, if I tell you how we know it's eight thousand miles；for without ever having been through the World, we do know how far it is.

This is how we know. It's a funny thing, but every ball, whether it is a little ball or a medium-sized ball or a great big ball, is always just a little more than three times as big round as it is through.I have often wondered why this was so—why a ball shouldn't be exactly three times or four times or five times as big round as through, but it isn't.You can try it yourself if you don't believe it.Take an apple or an orange and measure it around and then cut it and measure it through.

Now we know the World is a ball, a huge ball, and yet as it is a ball it must, like all other balls, be a little more than three times as big around as it is through. It is twenty-five thousand miles round the World, because men have actually measured that.So we know that the distance through must be about eight thousand miles, as twenty-five is a little more than three times eight.That is not geography；it's arithmetic.If you want to use big words for“around”and“through，”as they do in geographies, you must say“circumference”for“around”and“diameter”for“through”—which mean the same thing：the circumference of the World is twenty-five thousand and the diameter is eight thousand.

The outside of the World is a crust of rock like the skin of a baked potato over the hot inside. Some of the crust that you go through first is in layers, like layers in a jelly-cake, one layer after another, only these rock layers look as if they were made of sand and

的了。那個時候，我還太小，根本就理解不了。我不知道你們是不是也太小，要是我跟你們解釋我們為何知道地球直徑是八千英里的話，你們是不是能夠理解，因為我們確實無須穿過整個地球，便知道地球的直徑是多少。

下面就是我們得知地球直徑的方法。有一個非常有意思的現象：任何一個球體，無論它是一個小球，還是一個中等尺寸的球體，抑或是一個非常巨大的球體，其最大一圈的長度始終都是球體對直距離的三倍多一點兒。我也一直都想知道，為什么會是這樣：一個球體最大一圈的長度，為什么不是正好等于其對直距離的三倍、四倍或者五倍，可事實就是如此。要是不信的話，你們自己就可以試一試。你們不妨拿出一個蘋果或者一個橙子，量一量它一圈的長度，然后再從中切開，量一量它們的對直距離。

既然我們知道地球是一個球體、一個巨大的球體，那么，作為一個球體，它最大一圈的長度，也必定是整個地球對直距離的三倍多一點兒。環繞地球一圈的長度是二萬五千英里，因為人類已經實地測量過了。所以，我們便知道，地球的對直距離一定是八千英里左右，因為二萬五千英里正好是八千英里的三倍多一點兒。這可不是個地理問題，而是一個算術問題了。要是你們想要像地理學上一樣，用更難一點兒的詞匯來代替“圈長”和“對直距離”的話，那么“圈長”對應的就是“周長”，“對直距離”對應的就是“直徑”，它們所指的都是同一回事兒：地球的周長是二萬五千英里，而直徑就是八千英里。

地球的表面，是一層由巖石組成的地殼，它就像熱乎乎的烤土豆外面包裹著的

shells, or coal or little stones, and that's what they are made of. If you could cut the World in half as if it were an apple, it might look something like the picture on the next page.We call it a“Cross Section.”

那層烤焦了的外皮一樣。假如向下挖掘的話，那么最先挖到的那一部分地殼是分層排列的，就像果凍蛋糕那樣，一層一層地堆疊著，只是地殼里的這些分層，似乎都是由沙子和貝殼或者煤炭和小石子構成的，而事實上，它們也的確是由這些東西組成的。如果你們能夠像切蘋果那樣，把地球切成兩半的話，就會呈現出上圖所示的樣子來。我們稱之為“橫截面”。

有些巖層之間還有煤炭，就像果凍蛋糕里的果凍似的，其他地方則有黃金、白銀、鉆石和紅寶石，還有些巖層里則儲存著石油。人們之所以會向下打井，鉆穿這

Between some of the layers of rock there is coal like jelly in a jelly-cake and in other places there are gold and silver and diamonds and rubies, and in some of the rock there are pools of oil. That's why men dig wells down through these layers of rock to get oil, and that's why men dig mines to get coal and gold.

And still farther down the rock is not in layers—it is just solid rock；and still farther down it gets hotter and hotter where the world has not cooled off even yet, until the rock is no longer solid, but melted.

Whenever you see a chimney you know there is a furnace beneath it, and when smoke and fire come out of its top you know there is a fire in the furnace. Well, there are many places on the World where fire and smoke come out of the ground as if through a chimney from a fiery furnace.These places are called volcanoes.

Why was the World made of rock instead of brass or glass or china?Why is the World shaped like a ball and not like a box, a roller, or an old shoe?

些巖層來開采石油，之所以會挖掘礦井來開采煤炭和黃金，原因就在于此。

而巖石層之下更深的地方，就不再是分層排列的，而全都是基巖了。再往下去，巖石還變得越來越熾熱，因為地球的這一部分至今都還沒有冷卻下來，使得巖石不再是固體，而成了熔巖。

無論什么時候，只要一看到煙囪，你們就知道，煙囪下面肯定有座爐子，如果煙囪頂上還冒出煙火來，那你們就會知道，爐子里肯定是生了火。好吧，地球上有好多的地方，地上也會冒出煙和火來，就像是從一座燃著的爐子上方的煙囪里冒出來似的。這些地方，就稱為火山。

為什么地球是由巖石構成的，而不是由黃銅、玻璃或者瓷器構成的呢？為什么地球的樣子會是一個球體，而不是像一個盒子、一個滾筒或者一只舊鞋子呢？