THE 
BRITISH ENCYCLOPEDIA. 
ABA 
A The first letter of the alphabet, and one 
) of the five vowels, is pronounced vari- 
ously; sometimes open, as in the words 
talk, war ; and at others close, as in take, 
wake. 
A is also used, on many occasions, as a 
character, mark, or abbreviation. Thus, in 
the calendar, it is the first of the dominical 
letters : among logicians, it denotes an uni- 
versal affirmative proposition: as a numeral, 
A signified 1 among the Greeks; but among 
the Romans, it denoted 500, and withji 
dash over it, thus A, 5000. A, a, or aa, 
among physicians, denote ana, or an equal 
weight, or quantity, of several ingredients. 
AAM, or Haam, a liquid measure used 
by the Dutch, equal to 288 pints English 
measure. 
ABACK, in sea language, signifies the 
situation of the sails when their surfaces are 
flatted against the mast. They may be 
brought aback, either by a sudden change 
of wind, or an alteration in the ship’s cqurse. 
They are laid aback to effect an immediate 
retreat, without turning either to the right 
or left, to avoid some immediate danger in 
a narrow channel, or when she has advanced 
beyond her station in the line of battle. 
ABACUS, in architecture, the uppermost 
member of the capital of a column. See 
Architecture. 
Abacus, among ancient mathematicians, 
was a table strewed over with dust, or 
sand, on which they drew their figures or 
schemes. 
Abacus, in arithmetic, an instrument for 
facilitating operations by means of counters. 
Its form is various ; but that chiefly used 
in Europe is made by drawing parallel 
VOL. I. 
ABA 
lines, distant from each other at least twice 
the diameter of a counter ; which, placed on 
the lowermost line, signifies 1; on the se- 
cond, 10; on the third, 100; on the fourth, 
1000; and so on. Again, a counter, placed 
in the' spaces between the lines, signifies 
only the half of what it would do on the 
next superior line. 
Abacus pythagoridus, a multiplication- 
tab! 3, or a table of numbers ready cast up, 
to facilitate operations in arithmetic. 
Abacus logisticus, is also a kind of multi- 
plication-table, in form of a right-angled 
triangle. 
Abacus harmonious, among musicians, de- 
notes the arrangement of the keys of a mu- 
sical instiument. 
Abacus, Grecian, an oblong frame, over 
which are stretched several brass wires, 
strung with little ivory balls, by the various 
arrangements of which all kinds of compu- 
tations are easily made. 
Abacus, Chinese, or Shwanpan, consists of 
several series of beads strqng on brass wires, 
stretched from the top to the bottom of the 
instrument, and divided in the middle by a 
crosspiece from side to side. In the up- 
per space every string has two beads, which 
are each counted for five ; and in the lowest 
space every string has five beads, of dif- 
ferent values, the first being counted as 
1, the second as 10, the third as 100, and 
so on. 
ABAFT, in sea-language, a term applied 
to any thing situated towards the stern of a 
vessel : thus a thing is said to be abaft the 
fore-mast, or main-mast, when placed be- 
tween the fore-mast, or main-mast, and the 
stern. 
B 
