воскресенье, 22 января 2017 г.

Revolving mirror

Вообще очень  интересно читать про старую технику эксперимента. Вот например вращающееся зеркало Чарльза Уитсона, про которое упоминалось в прошлой ссылке, что я приводил.

Английская Вики пишет, что с его помощью была измерена скорость электричества более корректно, нежели с использованием нескольких монахов, державшихся за провод. А также это устройство было использовано для измерения скорости света, ну и, как вы уже знаете, изучения электрической искры конденсатора.

Velocity of electricity

He achieved renown by a great experiment made in 1834 – the measurement of the velocity of electricity in a wire. He cut the wire at the middle, to form a gap which a spark might leap across, and connected its ends to the poles of a Leyden jar filled with electricity. Three sparks were thus produced, one at each end of the wire, and another at the middle. He mounted a tiny mirror on the works of a watch, so that it revolved at a high velocity, and observed the reflections of his three sparks in it. The points of the wire were so arranged that if the sparks were instantaneous, their reflections would appear in one straight line; but the middle one was seen to lag behind the others, because it was an instant later. The electricity had taken a certain time to travel from the ends of the wire to the middle. This time was found by measuring the amount of lag, and comparing it with the known velocity of the mirror. Having got the time, he had only to compare that with the length of half the wire, and he could find the velocity of electricity. His results gave a calculated velocity of 288,000 miles per second, i.e. faster than what we now know to be the speed of light (299,792.458 kilometres per second (186,000 mi/s)), but were nonetheless an interesting approximation.

It was already appreciated by some scientists that the “velocity” of electricity was dependent on the properties of the conductor and its surroundings. Francis Ronalds had observed signal retardation in his buried electric telegraph cable (but not his airborne line) in 1816 and outlined its cause to be induction.[2] Wheatstone witnessed these experiments as a youth, which were apparently a stimulus for his own research in telegraphy. Decades later, after the telegraph had been commercialised, Michael Faraday described how the velocity of an electric field in a submarine wire, coated with insulator and surrounded with water, is only 144,000 miles per second (232,000 km/s), or still less.

Wheatstone's device of the revolving mirror was afterwards employed by Léon Foucault and Hippolyte Fizeau to measure the velocity of light.

Upd. Гугл очень интересную ссылку подкинул, как можно реализовать опыт Уитсона в современных условиях. Ну что же, будем разбираться: http://www.energeticforum.com/renewable-energy/11853-anyone-feels-like-repeating-wheatstones-1834-experiment-disprove-einstein.html

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