英语听力文摘 English Digest 71、恒温调节器

　　Thermometers just tell you the temperature. Thermostats² need to do more than that. In addition to reading the air temperature, thermostats also turn your furnace on if the air gets too cool, and turn it off again when the air heats up.
How do they do this?
At the heart of many household thermostats is a type of thermometer called a bimetallic coil.
This is made from two long, thin strips of metal, usually brass⁴ and steel, that have been joined firmly together, face to face, like a metallic³ sandwich. This new strip, brass on one side and steel on the other, is then coiled into a spiral.
Remember that most substances expand when they’re heated and contract when they’re cooled. It’s also true that different substances expand and contract at different rates.
In a bimetallic coil, the brass expands and contracts a little bit more than the steel does over the same range of temperature. For example, if the temperature rises, the brass side of the strip will lengthen⁵ slightly more than the steel side. This makes the coil tighten⁶ and loosen with changing temperature.
In a thermostat¹, the bimetallic coil is fastened firmly at one end. The other end is free to move. Its motion, as the temperature changes, can be used to control your furnace.
For example, if the coil tightens⁷ as it cools, the free end can curl toward a metal contact that starts the furnace. As the air heats up and the coil loosens, the free end curls away from the contact and the furnace shuts off.
When you adjust the thermostat you move the contact. When the contact is closer to the end of the coil, it will take a smaller drop in temperature to activate⁸ the furnace and your house will be warmer. Sliding the contact away will keep your house cooler.
thermometer:温度计
thermostat:恒温器
furnace:火炉
bimetallic coil:双金属线圈
slide:滑动

1 thermostat   

n.恒温器

参考例句：

• The thermostat is connected by a link to the carburetor.恒温控制器是由一根连杆与汽化器相连的。
• The temperature is controlled by electronic thermostat with high accuracy.电子恒温器，准确性高。

2 thermostats   

n.恒温（调节）器( thermostat的名词复数 )

参考例句：

• This is the basic operating principle of many thermostats. 这是许多恒温箱的基本工作原理。 来自辞典例句
• Thermostats can be used to regulate the temperature of a room. 恒温器可用来调节室内温度。 来自辞典例句

3 metallic   

adj.金属的；金属制的；含金属的；产金属的；像金属的

参考例句：

• A sharp metallic note coming from the outside frightened me.外面传来尖锐铿锵的声音吓了我一跳。
• He picked up a metallic ring last night.昨夜他捡了一个金属戒指。

4 brass   

n.黄铜；黄铜器，铜管乐器

参考例句：

• Many of the workers play in the factory's brass band.许多工人都在工厂铜管乐队中演奏。
• Brass is formed by the fusion of copper and zinc.黄铜是通过铜和锌的熔合而成的。

5 lengthen   

vt.使伸长，延长

参考例句：

• He asked the tailor to lengthen his coat.他请裁缝把他的外衣放长些。
• The teacher told her to lengthen her paper out.老师让她把论文加长。

6 tighten   

v.(使)变紧；(使)绷紧

参考例句：

• Turn the screw to the right to tighten it.向右转动螺钉把它拧紧。
• Some countries tighten monetary policy to avoid inflation.一些国家实行紧缩银根的货币政策，以避免通货膨胀。

7 tightens   

收紧( tighten的第三人称单数 )； （使）变紧； （使）绷紧； 加紧

参考例句：

• One set of provisions tightens emission standards. 一套使排放标准更加严格的规定。 来自英汉非文学 - 环境法 - 环境法
• Requires no special tools or fittings; hand tightens to relief valve outlet. 不需要专用工具或管件；用手将其紧固到安全阀上即可。

8 activate   

vt.使活动起来，使开始起作用

参考例句：

• We must activate the youth to study.我们要激励青年去学习。
• These push buttons can activate the elevator.这些按钮能启动电梯。