英國學(xué)生科學(xué)讀本 Lesson 94 一副風箱(1)

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第94課 一副風箱

Have you a pair of bellows at home? If you have, I hope that you will examine them carefully, and try to see how they are made, and to understand their use. Perhaps you have heard of the boy who cut the bellows open to see where the wind came from. If you will read what I have to tell you, you will not need to do anything so foolish.

你的家里是否有一副風箱呢? 如果有的話, 希望你能夠仔細觀察它的構(gòu)造并了解它的用途。也許你聽說過, 有的孩子會拆開風箱, 看看這些風到底是從哪里來的。如果你看了我的介紹, 就不會做出這樣的傻事了。

A pair of bellows consists of two rounded pieces of thin wood, which are joined together at the edges by a folded piece of leather. Each board has a short handle by which the bellows can be opened and closed.

一副風箱包括兩塊輕薄的圓形木片, 通過邊緣處一片交疊的皮革固定在一起。兩塊木片各有一個短短的把手, 利用把手, 我們可以開閉風箱。

In the centre of the under or lower board there is a round hole, and if you put your finger into this hole, you can feel that it is closed inside by a loose flap of leather. This leather flap is called a "valve. " It opens inwards. When you separate the handles of the bellows and make the space inside larger, the outside air forces open the valve, rushes in through the hole, and fills the bellows.

在下方木片的中心位置上有一個圓孔, 你把手指伸入孔中, 就會感覺到其內(nèi)部被一個松動的皮革蓋板所封閉。這個皮革蓋板就是“閥門”, 它朝里打開。如果你拉開風箱的把手, 使得內(nèi)部空間變大, 外部空氣就會迫使閥門打開, 沖出圓孔, 進入風箱內(nèi)部。

But when you push the handles together, the air inside presses down the valve and closes the hole; so that the air has to pass out through the metal spout or "nozzle, " which is placed at the end of the bellows opposite to the handles.

然而, 當你將兩個把手靠近時, 內(nèi)部的空氣就會壓下閥門并關(guān)閉圓孔;如此一來, 空氣就只能通過把手反方向另一端的金屬噴口或者“噴嘴”透出。

A valve is somewhat like a trap-door, and is used for allowing a fluid—usually air or water—to pass through in one direction but not in the other. You can make a valve by cutting a hole through a big cork, and then covering the hole with a piece of paper a little smaller than the cork. You must pin down or gum the paper to the cork at one side only. You will then find that you can blow through the hole in the cork in one direction, but not in the other.

閥門是一種類似活板門的設(shè)施, 通常用于確保流體——一般是空氣或水——能夠向某一個固定的方向流動。你也可以制造閥門：在大木塞上鉆一個洞, 然后利用一張比木塞稍小的紙來擋住這個洞。必須將這張紙釘在或者黏貼在木塞的一面。隨后你就會發(fā)現(xiàn), 你只能從一個方向上通過這個洞向木塞吹氣, 而另一個方向則不行。

If you keep your finger inside the hole in the bellows by which the air enters, the bellows will not do their work properly;

如果你將手指堵在風箱中空氣進出的圓孔上, 風箱就無法正常工作了。

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