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Thursday, 19 August 2010 22:50 |
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In 1678 the great Dutch
physicist Christian Huygens (1629-1695) wrote a treatise called Traite de
la Lumiere on the wave theory of light, and in this work he stated that
the wavefront of a propagating wave of light at any instant conforms to the
envelope of spherical wavelets emanating from every point on the wavefront at
the prior instant (with the understanding that the wavelets have the same
speed as the overall wave). An illustration of this idea, now known as
Huygens' Principle, is shown below. |
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Thursday, 19 August 2010 22:50 |
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If two events, denoted by A and B, are mutually exclusive and have
the individual probabilities P(A) and P(B), then the probability of "A
or B" is just the sum of the individual probabilities, i.e.,
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Thursday, 19 August 2010 22:48 |
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In 1885 a Swiss secondary
school teacher named Johann Jacob Balmer published a short note (entitled “Note
on the Spectral Lines of Hydrogen”, Annalen der Physik und Chemie 25,
80-5) in which he described an empirical formula for the four most prominent
wavelengths of light emitted by hydrogen gas. These wavelengths had been
measured with great precision by Vogel and Huggins, giving the four values
6562.10, 4860.74, 4340.10, and 4101.20 Angstroms (10-10 m).
Balmer's note does not make clear whether he was also aware of the measured
series limit, l¥ = 3645.6 A, or whether he deduced this himself. In
any case, one can find by numerical experimentation that the four
characteristic wavelengths are closely proportional to the following products
of small primes
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Page 1 of 65 |
The Hofstadter Butterfly
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