值得抄写的短篇美文怎么写？( 七 )

Yet, people began to understand how electricity works only a little more than two centuries ago.Nature has apparently been experimenting in this field for million of years.Scientists are discovering more and more that the living world may hold many interesting secrets of electricity that could benefit humanity.
All living cell send out tiny pulses of electricity.As the heart beats, it sends out pulses of record; they form an electrocardiogram, which a doctor can study to determine how well the heart is working.The brain, too, sends out brain waves of electricity, which can be recorded in an electroencephalogram.The electric currents generated by most living cells are extremely small – often so small that sensitive instruments are needed to record them.But in some animals, certain muscle cells have become so specialized as electrical generators that they do not work as muscle cells at all.When large numbers of these cell are linked together, the effects can be astonishing.
The electric eel is an amazing storage battery.It can seed a jolt of as much as eight hundred volts of electricity through the water in which it live.( An electric house current is only one hundred twenty volts.) As many as four-fifths of all the cells in the electric eel’s body are specialized for generating electricity, and the strength of the shock it can deliver corresponds roughly to length of its body.
10．Scientific Theories
In science, a theory is a reasonable explanation of observed events that are related.A theory often involves an imaginary model that helps scientists picture the way an observed event could be produced.A good example of this is found in the kinetic molecular theory, in which gases are pictured as being made up of many small particles that are in constant motion.
A useful theory, in addition to explaining past observations, helps to predict events that have not as yet been observed.After a theory has been publicized, scientists design experiments to test the theory.If observations confirm the scientist’s predictions, the theory is supported.If observations do not confirm the predictions, the scientists must search further.There may be a fault in the experiment, or the theory may have to be revised or rejected.
Science involves imagination and creative thinking as well as collecting information and performing experiments.Facts by themselves are not science.As the mathematician Jules Henri Poincare said, ―Science is built with facts just as a house is built with bricks, but a collection of facts cannot be called science any more than a pile of bricks can be called a house.‖
Most scientists start an investigation by finding out what other scientists have learned about a particular problem.After known facts have been gathered, the scientist comes to the part of the investigation that requires considerable imagination.Poible solutions to the problem are formulated.These poible solutions are called hypotheses.

值得抄写的短篇美文怎么写？

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