Adding a Dimension: 17 Essays on the History of Science by Isaac Asimov

Author:Isaac Asimov [Asimov, Isaac]
Language: eng
Format: epub
ISBN: 9780380002788
Google: VfdHAQAAIAAJ
Amazon: 0380002787
Goodreads: 837153
Published: 2016-01-16T18:22:25+00:00

100

ADDING A DIMENSION

THE LIGHT THAT FAILED

101

the same it did prove the earth was moving with respect to the stars, Foucault went further. He measured the velocity of light through for if the earth were motionless, the telescope would not have to be water and other transparent media (you could do this with laboratory tilted at all, and the star would not seem to move.

methods but not with astronomical methods). He discovered in this It gave additional information, too. The amount of the aberration way that light moved more slowly in water than in air.

of light depended on two factors: the velocity of light and the velocity This was important. If the particle theory of light were true, light of the earth’s motion in its orbit. The latter was known (about I8i should move more rapidly in water than in air; if the wave theory miles per second); therefore the former could be calculated. Bradley’s of light were true, light should move more slowly in water than in air.

estimate was that light bad a velocity of about 188,500 miles per By the mid-nineteenth century, to be sure, most physicists had acsecond. This was only 1.2 percent above the true value.

cepted the wave theory. Nevertheless, Foucault’s experiment was widely interpreted as having placed the final nail in the coffin of the Two independent astronomical methods had yielded figures for the I ,. particle theory.

velocity of light and improved observations showed the two methods I

yielded roughly the same answer. Was there no way, however, in And now we come to Michelson. Michelson had been born in which the velocity could be measured on earth, under conditions con1852 in a section of Poland that at that time was under Gennan rule, trolled by the experimenter?

and be was brought to the United States two years later. His family The answer was yes, but the world had to wait a century and a did not follow the usual pattern of settling in one of the large East quarter after Bradley’s discovery before a method was found. The Coast cities. Instead, the Michelsons made their way out to the far discoverer was a French physicist Armand Hippolyte Louis Fizeau West, a region which the forty-niners had just ripped wide open.

who returned to GaliJeo’s method but eliminated the personal ele

The Michelson family did well there ( as merchants, not as goldment. Instead of having an assistant return a second beam of light, miners), and young Albert applied for entrance into Annapolis in he had a mirror reflect the first one.

1869. He passed the necessary tests, but the son of a war veteran In 1849 Fizeau set up a rapidly turning toothed disk on one hill

(Civil War, of course) took precedence. It took the personal intop and a mirror on another, five miles away. Light passed through

. tervention of President Grant (with an assist from the Nevada conone gap between the teeth of the turning disk and was reflected by gressman who pointed out the political usefulness of such a gesture the mirror.

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