Seidel sum

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Lusitania sinking, illustration from The War of the Nations (New York), December 31, 1919. World War I, WWI. This image is one of three on the page. (See source file for the other two.)

7 of the World’s Deadliest Shipwrecks

July, 2006, Launch of Space Shuttle Discovery STS-121. See attached for full caption information.

Will Light-Speed Space Travel Ever Be Possible?

Easter Procession of Maria Santisima del Sacromonte in Granada, Spain. This statue is known as Virgen de los Gitanos or The Virgin of the Gypsies.

What is Holy Week?

Ahura Mazda - relief of the Zoroastrian god Ahura Mazda at the ancient ruins of Persepolis in Iran. Also known as Ormazd Zoroastrianism,

Which Religion Is the Oldest?

Rural Irish landscape, Sligo, Ireland.

Why Is Ireland Two Countries?

New Zealand. Political/Physical map. Includes locator.

Where Is “Old Zealand”?

Small, white rat (genus Rattus) on a glass table. (rodent, laboratory, experiment)

Cruel and Unusual Punishments: 15 Types of Torture

Seidel sum

optics

Learn about this topic in these articles:

model for lens aberrations

In optics: Seidel sums
If a lens were perfect and the object were a single point of monochromatic light, then, as noted above, the light wave emerging from the lens would be a portion of a sphere centred about the ideal image point, lying in the paraxial…
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