人行考试英语资料.docxVIP

Recent research has claimed that an excess of positive ions in the air can have an ill effect on peoples physical or psychological health. What are?positive ions？Well，the air is full of ions，electrically charged particles，and generally there is a rough balance between the positive and the negative charged. But sometimes this balance becomes disturbed and a larger proportion of positive ions are found. This happens naturally before?thunderstorm，earthquakes when winds such as the Mistral，Hamsin or Sharav are blowing in certain countries.?Or it can be caused by a build-up of static electricity indoors from carpets or clothing made of man-made fibres，or from TV sets，duplicators or computer display screens. 　　When a large number of positive ions are present in the air many people experience unpleasant effects such as?headaches，fatigue，irritability，and some particularly sensitive people suffer nausea or even mental disturbance. Animals?are also affected，particularly before earthquakes，snakes have been observed to come out of hibernation，rats to flee from their burrows，dogs howl and cats jump about unaccountably. This has led the US Geographical Survey to fund a network of volunteers to watch animals in an effort to foresee such disasters before they hit vulnerable areas such as?California. 　　Conversely，when large numbers of negative ions are present，then people have a feeling of well-being. Natural conditions that produce these large amounts are near the sea，close to waterfalls or fountains，or in any place where?water?is sprayed，or forms a spray. This probably accounts for the beneficial effect of a holiday by the?sea，?or in the?mountains?with tumbling streams or 　　To increase the supply of negative ions indoors，some scientists recommend the?use of ionisers：small portable machines，which generate negative ions. They claim that ionisers not only clean and refresh the air but also improve the health of people sensitive to excess positive ions. Of course，there are the detrac