ish writer on pure and applied mathematics,
was born at Norwich in 1776 and died on the 1st of March 1862. In 1806 he
was appointed mathematical master in the Woolwich Academy, and filled that
post for forty-one years. In 1823 he was made a fellow of the Royal
Society, and two years later received the Copley medal. Steam locomotion
received much attention at his hands, and he sat on the railway commissions
of 1836, 1839, 1842, 1845. He received many distinctions from British and
foreign scientific societies. Barlow's principal works are--_Elementary
Investigation of the Theory of Numbers_ (1811); _New Mathematical and
Philosophical Dictionary_ (1814); _Essay on Magnetic Attractions_ (1820).
The investigations on magnetism led to the important practical discovery of
a means of rectifying or compensating compass errors in ships. Besides
compiling numerous useful tables, he contributed largely to the
_Encyclopaedia Metropolitana_.

BARM (a word common to Teutonic languages), the scum formed on the top of
malt liquor when fermenting; yeast used to leaven bread, or to set up
fermentation in liquor.

BARMECIDES, more accurately BARMAKIDS, a noble Persian family which
attained great power under the Abbasid caliphs. Barmak, the founder of the
family, was a Persian fire-worshipper, and is supposed to have been a
native of Khorasan. According to tradition, his wife was taken for a time
into the harem of Abdallah, brother of Kotaiba the conqueror of Balkh, and
became the mother of Khalid b. Barmak the Barmecide. Barmak subsequently
(about A.D. 736) rebuilt and adorned his native city of Balkh after the
rebellion of Harith. The family prospered, and his grandson Ya[h.]y[=a] b.
Khalid was the vizier of the caliph Mahdi and tutor of Har[=u]n al-Rashid.
His sons Fadl and Ja'far (the Giafar of the _Arabian Nights_) both occupied
high offices under Har[=u]n. The story of their disgrace, though romantic,
is not improbable. Har[=u]n, it is said, found his chief pleasure in the
society of his sister 'Abb[=a]sa and Ja'far, and in order that these two
might be with him continuously without breach of etiquette, persuaded them
to contract a purely formal marriage. The conditions were, however, not
observed and Har[=u]n, learning that 'Abb[=a]sa had borne a son, caused
Ja'far suddenly to be arrested and beheaded, and the rest of the family
except Mahommed, Ya[h.]y[=a]'s brother, to be imprisoned and deprived of
their property. It is probable, h