Year 400 ce

Chemistry

The term chemistry is used for the first time by Alexandrian scholars for the activity of changing matter. See also 300 ce Chemistry.

The Buddhist monastery Bamiyan is carved into the sandstone cliffs of the foothills of the Hindu Kush (Afghanistan), housing 1000 monks and a 37-m- (120-ft-) high statue of Buddha. The giant statute and another of Buddha will be demolished by the Afghan government, run by a group called the Taliban, in March 2001. See also 489 ce Archaeology.

The early Anasazi people enter what is now called the four corners region (where Colorado, Utah, Arizona, and New Mexico come together at right angles). They are hunter-gatherers, living in caves along rocky cliffs and canyon walls. See also 500 ce Construction.

The overshot water wheel, in which water that has been retained in a mill pond is directed by means of a chute over the top, is developed in the Roman Empire (although it probably originated about 200 years earlier). By controlling the level of the pond feeding the water with sluices, the water mill can function most of the year and be operated only when needed for grinding grain or extracting oil from olives. See also 25 bce Energy.

About this time the Chinese learn how to make steel by forging together cast and wrought iron. See also 500 bce Materials.

Theon and Hypatia of Alexandria prepare editions of Euclid's Elements and his Optics.

Hypatia of Alexandria develops the hydroscope (also called hydrometer), an instrument for determining the specific gravity of a liquid. It consists of a sealed tube weighted at one end. The depth the tube sinks into a liquid is the measure for its specific gravity. She also improves the astrolabe. See also 200 bce Astronomy.

The Chinese invent the umbrella. See also 1 ce Transportation.