|
|
Text 4. LIGHT TRAVELS MORE SLOWLY IN WATER THAN IN AIR
In the 17th century, scientists started to investigate light, and aimed at establishing whether it had a finite, measurable speed. To be more precise, in 1690, Christiaan Huygens published his theory reporting that light is a pressure wave that moves in a fluid called ether. The scientist believed that light as a longitudinal wave. He also predicted that the wave would travel more slowly through glass or water than through air.
In 1704, the famous Isaac Newton published his theory of light under which light was considered a stream of “corpuscles,” or particles. According to the Newton’s explanation for refraction, light travels faster after it passes from air into water. His estimates for the speed of light were based on astronomical phenomena, showing how fast light can travel through space. French physicist Hippolyte Fizeau was the first to carry out the first terrestrial measurement in 1849. A beam of light was shone through a gap between the teeth of a rotating cogwheel, and such light was reflected by a mirror positioned 5 miles (8 km) away, and passed back through the next gap between the wheel’s teeth. By measuring the precise speed of rotation, together with time and distance, Fizeau managed to calculate the speed of light as 194,489 miles/s (313,000 km/s).
Contradicting Newton
In 1850, Fizeau in collaboration with physicist Leon Foucault adapted his apparatus by reflecting the beam of light off a rotating mirror instead of passing it through the cogwheel. Light shining at the rotating mirror would now be reflected toward the distant mirror when the rotating mirror was at the correct angle. Light returning from the fixed mirror was reflected by the rotating mirror again, but since this mirror had moved while the light was traveling, it was not reflected directly back toward the source. This allowed to calculate the speed of light from the angle between the light going to and from the rotating mirror and the speed of rotation of 11 the mirror. Having applied this apparatus, Foucault established that light traveled more slowly in water than in air. So, he claimed that light could not be a particle, and the experiment was viewed at the time as a refutation of Newton’s theory of corpuscles. Foucault refined his apparatus further, and in 1862, measured the speed of light in air as 185,168 miles/s (298,000 km/s), which is remarkably close to today’s value of 186,282 miles/s (299,792 km/s).
Exercises
1. Read the text again and translate it orally.
2. Make a detailed plan of the text paying attention to the key ideas of each paragraph
3. Form verbs from the following words:
An aim – a publication – a movement – a prediction – a consideration – a measurement – rotating – a reflection – a collaboration – a calculator – an application
4. Find Russian equivalents to the following words and expressions:
To aim at – finite – to be more precise – to predict – according to – an estimate – to measure – to calculate – distant – a source – to apply
5. Translate the following sentences into Russian paying attention to the underlined words:
• In the 17th century, scientists started to investigate light, and aimed at establishing whether it had a finite, measurable speed.
• According to the Newton’s explanation for refraction, light travels faster after it passes from air into water.
• By measuring the precise speed of rotation, together with time and distance, Fizeau managed to calculate the speed of light.
• Having applied this apparatus, Foucault established that light traveled more slowly in water than in air.
6. Answer the following questions:
• Who was the first to report that light is a pressure wave that moves in a fluid called ether?
• What did Christiaan Huygens predict?
• How did Isaac Newton consider light?
• How was it possible to measure the speed of light in water?
• What was the major idea within the investigation of light?
• How did Newton explain refraction?
• Why is Hippolyte Fizeau important in terms of scientific investigation?
• What was the idea of further adaptation of Fizeau’s apparatus? 12 7. Finish the following sentences:
• The scientist believed that …
• According to the Newton’s explanation for refraction …
• A beam of light was shone through a gap between …
• Light shining at the rotating mirror would now be reflected toward …
• Measuring the speed of light in water was now able by …