Acidometer.
A hydrometer or areometer used to determine the specific gravity of
acid. They are employed in running storage batteries, to determine when
the charging is completed. (See Areometer.)
Aclinic Line.
A terrestrial element; the locus on the earth's surface of no
inclination of the magnetic needle; the magnetic equator. (See Magnetic
Elements.)
Acoustic Telegraphy.
The system of sound-reading in telegraphy, universally used in the Morse
system. The direct stroke of the armature of the electro-magnet and its
"back stroke" disclose to the ear the long and short strokes, dots and
lines, and long and short spaces as produced by the dispatcher of the
message. In the Morse system a special magnet and armature is used to
produce the sound called the "sounder;" in other systems, e. g.,
Steinheil's and Bright's apparatus, bells are used. (See Alphabets,
Telegraphic.)
Acoutemeter.
A Hughes audiometer or sonometer applied to determining the quality of a
person's hearing (See Hughes' Induction Balance,--Audiometer). The
central coil by means of a tuning fork and microphone with battery
receives a rapidly varying current tending to induce currents in the
other two coils. Telephones are put in circuit with the latter and pick
up sound from them. The telephones are applied to the ears of the person
whose hearing is to be tested. By sliding the outer coils back and forth
the intensity of induction and consequent loudness of the sounds in the
telephones is varied. The position when the sounds grow so faint as to
be no longer audible, gives the degree of delicacy of the person's
hearing. By using a single telephone the same apparatus affords a means
of testing the relative capacity of the right and left ears.