第3章　地球的内部

还在很小的时候，我就很喜欢打破砂锅问到底。至少来说，我的奶妈是这样认为的。

有一天，我正跟着她沿着市里的人行道散步，我问她说：

“简，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，还是土。”她回答道。

“好吧，那下面又是什么呢？”我问道。她的回答可没有让我觉得满意。

“噢，没有什么了吧，我可不知道。你为什么总是这样喜欢刨根问底呢？”她问道。

我知道，泥土下面肯定是有某种东西的，我就是想知道，那种东西究竟是什么，谁叫我喜欢刨根究底呢。

我曾经听说，坏孩子死后，会去地下的某个地方，或许是一个大洞穴吧，因此，我希望弄明白，究竟是不是那么回事。

于是，我便下定决心，要向下挖穿整个地球，并且一直向下、向下、向下挖掘，直到我抵达地球的那一边，那样一来，我就知道情况究竟是不是那样的了。你们都知道，当时我还是个很小很小的小男孩哩。我拿起一把锡制的铲子，开始在我家后院的葡萄架后挖出一个洞来。在那里进行挖掘，就没人知道我在干什么。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，保守住这个秘密。我干了一天又一天，起初挖出的都是松软的泥土，很容易挖掘；可接下来，我就挖到结实的土层，很难挖下去了。我挖出了一个洞，站在里面，洞子只有我的腰部那么深。

然后，有天傍晚，我的父亲问道：“后院里那个洞是干什么用的？”

我的秘密便公之于众了。我把这一切告诉父亲时，他并没有笑起来（起码也是没有哈哈大笑），而是问我，知不知道自己必须挖多远才能挖穿。

“你向下挖掘出的深度，能够达到华盛顿纪念碑向上耸立的那种高度吗？”他问道。

虽然觉得自己可能做得到，但我还是有一点儿怀疑，因为华盛顿纪念碑看上去，可高得很呢。

“人类向下挖掘的深度，已经达到华盛顿纪念碑高度的好多、好多倍了，”父亲告诉我说，“可从来没有挖穿过，或者接近挖穿过地球呢。你必须挖到有华盛顿纪念碑高度的几千倍深，才能挖到地心。地球的直径有八千英里，而且其中绝大部分都是岩石，全都是岩石，好多好多的岩石，没有其他的东西。”

于是，我便不再挖下去了。

“如果说到现在为止，还没有人挖穿过整个地球，那您又怎么知道地球的直径是八千英里呢？”那个喜欢刨根问底的孩子问道。我不记得父亲当时是怎样回答我

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。那个时候，我还太小，根本就理解不了。我不知道你们是不是也太小，要是我跟你们解释我们为何知道地球直径是八千英里的话，你们是不是能够理解，因为我们确实无须穿过整个地球，便知道地球的直径是多少。

下面就是我们得知地球直径的方法。有一个非常有意思的现象：任何一个球体，无论它是一个小球，还是一个中等尺寸的球体，抑或是一个非常巨大的球体，其最大一圈的长度始终都是球体对直距离的三倍多一点儿。我也一直都想知道，为什么会是这样：一个球体最大一圈的长度，为什么不是正好等于其对直距离的三倍、四倍或者五倍，可事实就是如此。要是不信的话，你们自己就可以试一试。你们不妨拿出一个苹果或者一个橙子，量一量它一圈的长度，然后再从中切开，量一量它们的对直距离。

既然我们知道地球是一个球体、一个巨大的球体，那么，作为一个球体，它最大一圈的长度，也必定是整个地球对直距离的三倍多一点儿。环绕地球一圈的长度是二万五千英里，因为人类已经实地测量过了。所以，我们便知道，地球的对直距离一定是八千英里左右，因为二万五千英里正好是八千英里的三倍多一点儿。这可不是个地理问题，而是一个算术问题了。要是你们想要像地理学上一样，用更难一点儿的词汇来代替“圈长”和“对直距离”的话，那么“圈长”对应的就是“周长”，“对直距离”对应的就是“直径”，它们所指的都是同一回事儿：地球的周长是二万五千英里，而直径就是八千英里。

地球的表面，是一层由岩石组成的地壳，它就像热乎乎的烤土豆外面包裹着的

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.”

那层烤焦了的外皮一样。假如向下挖掘的话，那么最先挖到的那一部分地壳是分层排列的，就像果冻蛋糕那样，一层一层地堆叠着，只是地壳里的这些分层，似乎都是由沙子和贝壳或者煤炭和小石子构成的，而事实上，它们也的确是由这些东西组成的。如果你们能够像切苹果那样，把地球切成两半的话，就会呈现出上图所示的样子来。我们称之为“横截面”。

有些岩层之间还有煤炭，就像果冻蛋糕里的果冻似的，其他地方则有黄金、白银、钻石和红宝石，还有些岩层里则储存着石油。人们之所以会向下打井，钻穿这

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?

些岩层来开采石油，之所以会挖掘矿井来开采煤炭和黄金，原因就在于此。

而岩石层之下更深的地方，就不再是分层排列的，而全都是基岩了。再往下去，岩石还变得越来越炽热，因为地球的这一部分至今都还没有冷却下来，使得岩石不再是固体，而成了熔岩。

无论什么时候，只要一看到烟囱，你们就知道，烟囱下面肯定有座炉子，如果烟囱顶上还冒出烟火来，那你们就会知道，炉子里肯定是生了火。好吧，地球上有好多的地方，地上也会冒出烟和火来，就像是从一座燃着的炉子上方的烟囱里冒出来似的。这些地方，就称为火山。

为什么地球是由岩石构成的，而不是由黄铜、玻璃或者瓷器构成的呢？为什么地球的样子会是一个球体，而不是像一个盒子、一个滚筒或者一只旧鞋子呢？