11. Retell the text.

12. (A) Fill in the blanks with prepositions, if necessary; (b) retell the text:

Jack London

The great American writer Jack London was born ... the town of San Frincisco in 1876. The young boy longed ... knowledge, but Jack's father could not send him ... school, as the family was very poor. London began working when he was quite young. He sold different newspapers ... the streets. ... the age ... fourteen he began to work ... a factory. Then he worked as a fisherman. He had to work many hours ... a day. Nevertheless he experienced a great want and count­less hardships ... that time. In spite of his hard work he was very fond ... reading and read very much. He studied …school and later on ... the university. He took great interest both ... history and ... philosophy. ... 1896 London started ... Alaska for the yellow metal. He did not live ...the North. ... a long time. Soon he came back ... San Francisco, and became famous as a writer. He greatly contributed ... the de­velopment ... progressive American literature. ... present his name is known all over the world.

LESSON TEN

FROM THE HISTORY OF ELECTRICITY

There are two types of electricity, namely, electricity at rest or in a static condition and electricity in motion, that is, the electric current. Both of them are made up of electric charges, static charges being at rest, while electric current flows and does work. Thus they differ in their ability to serve mankind as well as in their behavior.

Let us first turn our attention to static electricity. For a long time it was the only electrical phenomenon to be ob­served by man. As previously mentioned (see Lesson 7) at least 2,500 years ago, or so, the Greeks knew how to get electricity by rubbing substances. However, for practical purposes static electricity was not much more useful than lightning. Indeed, the electricity to be obtained by rubbing objects cannot be used to light lamps, to boil water, to run electric trains, and so on. It is usually very high in voltage, difficult to control; besides it discharges in no time.

As early as 1753, Franklin made an important contribution to the science of electricity. He was the first to prove that unlike charges are produced due to rubbing dissimilar objects. To show that the charges are unlike and opposite he decided to call the charge on the rubber—negative and that on the glass—positive. ' -

In this connection one might remember our Russian-Асademician Petroff. He was the first to carry on experiments and observations on the electrification of metals by rubbing them one against another. As a result he was the first scien­tist in the world who solved that problem.

So far, almost nothing was said about the electric current. Who does not know that the first man to produce it was Volta. His discovery developed out of Galvani's experiments with the frog. Various writers retell that story in quite different ways. In fact, Galvani observed that the legs of a dead frog jumped as a result of an electric charge. He tried his exper­iment several times and every time he obtained the same

Alessandro Volta (1745-1827)

result. He thought that electricity was generated within the leg itself.

This thought was not so very strange because he could not help remembering the electric fish which possessed the prop­erty of giving more or less, strong shocks.

As previously mentioned, the discovery of the electric current was made possible owing to Volta after whom the" unit of electric pressure, the volt, was named.

Volta was born at Como, in Italy, in February 18, 1745.For some years, he was a teacher of physics in his home town. Later on he became professor of natural sciences at the Uni­versity of Pavia. After his famous discovery he travelled in many countries, among them France, Germany and England. He was also invited to Paris to lecture on the newly discovered chemical source of continuous current. In 1819 he returned to Como where he spent the rest of his life. Volta died at the age of 82.

Volta took great interest in Galvani's researches. He began to carry on similar experiments and soon found out that the electric source was not within the frog's leg itself, but was, the result of the contact of both dissimilar metals used during his observations. However, to carry on experiments of such a kind was not an easy thing to do. He spent the next few years trying to invent a source of a steady, continuous cur­rent. To increase the effect obtained with one pair of metals, Volta increased- the number of these pairs. Thus the voltaic pile consisted of a layer of copper and a layer of zinc placed one above another with a layer of flannel moistened in salt water between them. In this way the voltaic pile looked like a thick sandwich containing copper, zinc, flannel moistened in salt water, copper, zinc, flannel, and so on. A wire was connected to the first disc of copper and to the last disc of zinc.

The year 1800 is a good date to be remembered: for the first time in the world's history a steady, continuous current was generated.

Exercises