Torr

The torr (symbol: Torr) is a unit of pressure based on an absolute scale, now defined as exactly 1/760 of a standard atmosphere. Thus one torr is exactly 7005101325000000000♠101325/760 pascals (~133.3 Pa).

Historically, one torr was intended to be the same as one "millimetre of mercury". However, subsequent redefinitions of the two units made them slightly different (by less than 6993150000000000000♠0.000015%). The torr is not part of the International System of Units (SI), but it is often combined with the metric prefix milli to name one millitorr (mTorr) or 0.001 Torr.

The unit was named after Evangelista Torricelli, an Italian physicist and mathematician who discovered the principle of the barometer in 1644.

Nomenclature and common errors

The unit's name "torr" is written in lower case, while its symbol ("Torr") is always written with upper-case initial; including in combinations with prefixes and other units, as in "mTorr" (millitorr) or "Torr·L/s" (torr-litres per second). The symbol (uppercase) should be used with prefix abbreviations (thus, mTorr and millitorr are correct, but mtorr and milliTorr are not).

John Torrey

John Torrey (August 15, 1796 – March 10, 1873) was an American botanist.

Biography

Torrey was born in New York City. He showed a fondness for mechanics, and at one time planned to become a machinist, but when he was 15 or 16 years of age his father received an appointment to the state prison at Greenwich Village, New York, where he was tutored by Amos Eaton, then a prisoner and later a pioneer of natural history studies in America. He thus learned the elements of botany, as well as something of mineralogy and chemistry. In 1815 he began the study of medicine with Wright Post, qualifying in 1818. He opened an office in New York City, and engaged in the practice of medicine, at the same time devoting his leisure to botany and other scientific pursuits.

In 1817, he became one of the founders of the New York Lyceum of Natural History (now the New York Academy of Science), and one of his first contributions to this body was his Catalogue of Plants growing spontaneously within Thirty Miles of the City of New York (Albany, 1819). Its publication gained for him the recognition of foreign and native botanists. In 1824 he issued the only volume of his Flora of the Northern and Middle States. This used John Lindley's system of classifying flora, a way of classifying that was not commonly used in the United States.

Torr (surname)

Torr is an English surname. Notable people named Torr include