b. ? and d. about 1038

Arabian philosopher and mathematician. He was the first to correct the Platonic theory that rays of light are emitted by the eye. He discovered atmospheric refraction, and what we see the moon after it has set. He was aware that the atmoshere decreased in density with the height, and actually fixed its height at 58 1/2 miles. He showed that weights differed in a rare and a dense atmosphere. He understood center of gravity, and applied it to balances and steelyards. He recognized gravity as a force, though he made it diminish as the distance, and made it purely terrestrial. He had laws of falling bodies, and ideas of capillary attraction. He wrote “Optical Thesaurus,” published in Latin in 1572.

Friend: the Great Ruler, easily content,
Needs not the laws it has laborious been
The task of small professors to invent;
A single wheel impels the whole machine
Matter and spirit; yea, that simple law,
Pervading nature, which our Newton saw.
This taught the spheres, slaves to one golden rein,
Their radiant labyrinths to weave around
Creation’s mighty hearts: this made the chain,
Which into interwoven systems bound
All spirits streaming to the spiritual sun,
As brooks that ever into ocean run.

—Friendship: Schiller

b. March 28, 2005 and d. January 30, 1853

American mathematician. He built in 1837 the first observatory of importance in the U.S. On Feb. 2, 1847, four months after the discovery of Neptune, he identified it with a star observed by Lalande, in May, 1795. With Prof. Alexander D. Bache he determined differences of longitude by telegraph (1849), and he introduced the chronograph for recording observations. his parallactic tables (1834) simplified the computations of the phases of an occultation. he published “Periodical Meteors of August and November” (1841); “Researches Relative to the Planet Neptune” (1850); and “Ephemeris of the Planet Neptune for 1848-’52″ (1852).

In your astronomical studies, the Earth on which you dwell will stand forth in space a suspended ball, taking its place as one of the smallest of the planets, and like them, pursuing its appointed path—the arbiter of times and seasons. Beyond our planetary system, now extended, by the discovery of Neptune, to nearly three thousand millions of miles from the sun, and throughout the vast expanse of the universe, the telescope will exhibit to you new suns and systems of worlds, infinite in number and variety, sustaining, doubtless, myriads of living beings, and presenting new spheres for the exercise of divine power and beneficence.

—Science and Art: D. Brewster

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