Bibliography: Lord Rayleigh, Theory of Sound; H. Smith, The Making of Sound in the Organ and Orchestra; J. W. Capstick, Sound (Cambridge Natural Science Manuals); E. H. Barton, Text-book of Sound.

Acqui (a˙k′wē), a town of Northern Italy, 18 miles S.S.W. of Alessandria, a bishop's see. It has warm sulphurous baths, which were known to the Romans, and which still attract a great many visitors. Pop. 16,500.

Acre, a standard British measure of land, also used in the colonies and the United States. The imperial statute acre consists of 4840 sq. yards, divided into 4 roods. The old Scotch acre contains 6146.8 sq. yards, the old Irish acre 7840 sq. yards.

Acre (ā′kėr) (ancient Accho and Ptolemais), a seaport of Syria, in Northern Palestine, on the Bay of Acre, early a place of great strength and importance. Taken from the Saracens under Saladin in 1191 by Richard I of England and Philip of France; bravely defended by the Turks, assisted by Sir Sidney Smith, in 1799 against Napoleon; in 1832, taken by Ibrahim Pasha; in 1840, bombarded by a British, Austrian, and Turkish fleet, and restored to the Sultan of Turkey. The town was occupied by British troops under General Allenby in September, 1918. Pop. 10,000.

MUSICAL INTERVALS.—See Acoustics

Intervals in
Perfect Diatonic
Scale. 		Perfect
Diatonic Scale 		Diatonic Scale.
on System of
Equal
Temperament.
 Intervals in
Tempered Scale—
Mean tone.
(21/6 = 1.123).
Semitone.
(21/12= 1.059).
C 1 1.000
9/8 major tone tone.
D 9/8 = 1.125 22/12 = 1.123
10/9 minor tone tone.
E 5/4 = 1.250 24/12 = 1.260
16/15 limma semitone.
F 4/3 = 1.333 25/12 = 1.335
9/8 major tone tone.
G 3/2 = 1.500 27/12 = 1.498
10/9 minor tone tone.
A 5/3 = 1.667 29/12 = 1.682
9/8 minor tone tone.
B 15/8 = 1.875 211/12 = 1.888
16/15 limma semitone.
C′ 2 2.000
Major tone ratio = 9/8 = 1.125Limma tone ratio = 16/15 = 1.067
Minor " " = 10/9 = 1.111Semitone " = 21/12= 1.059
Mean " " = 22/12= 1.123

NOTES OF PERFECT DIATONIC SCALE (with their Frequencies)