Unit, Absolute.
A unit based on the three fundamental units of length, mass and time.
These units are the centimeter, gram and second. Each one in itself may
be termed a fundamental absolute unit. The system of such units is
termed the centimeter-gram-second system.
Unit, Angle.
A factor or datum in angular velocity, q. v. It is the angle subtended
by a portion of the circumference equal in length to the radius of the
circle. It is equal very nearly to 57.29578° or 57° 17' 44.8".
Unit, B. A.
This term, while logically applicable to any of the British Association
units, is often restricted to the ohm as formerly defined by the British
Association, the B. A. Unit of Resistance, q. v.
Unit, Fundamental.
The three units of length, mass and time, the centimeter, gram and
second, are termed fundamental units. On them is based the absolute
system of units, and on multiples of them the practical system of units.
Unit Jar.
A Leyden jar which is used as a unit of measure of charge.
It consists of a Leyden jar about 4 inches long and 3/4 inch diameter,
with about 6 square inches of its outer and the same of its inner
surface coated with tinfoil. It is placed between a source of
electricity and a larger jar or battery of jars which is to be charged.
The inner coating connects with the machine; the outer coating with the
jars to be charged. Short conductors terminating in knobs connect with
inner and outer coatings, and the knobs are adjusted at any desired
distance apart.
By the charging operation the large jar or battery of jars receives a
charge by induction, and the charge of the small jar is at first equal
to this quantity. After a while a spark passes from knob to knob,
discharging the small jar. This indicates the reception by the large
jars of the quantity of electricity represented by the charge of the
small jar. The charging goes on, and for every spark approximately the
same quantity of electricity is received by the larger jars.
The sparking distance m is directly proportional to the quantity of
electricity, and inversely proportional to the area of coated surface,
or is proportional to the potential difference of the two coats. This is
only true for short sparking distance, hence for accuracy the knobs
should be adjusted not too far from each other.