Everything in nature is bipolar, or has a positive and negative pole.
Some dynamos are bipolar, or have two poles, others are multipolar or have more than two.
If the connexion is only with one, the vesicle is called unipolar; if with two, bipolar; if with many, multipolar or stellate.
Unipolar spots are very seldom observed without some indication of the characteristics of bipolar groups.
The bipolar spot seems to be the dominant type, and the unipolar type a variant of it.
The design of Fig.10 has two poles in the field and two in the armature, and is what is known as the bipolar type.
The ends of this magnet, which are called poles, are bent up, and hence this type is called a bipolar receiver.
When two are used they are arranged on opposite sides of the armature, and form what is known as the bipolar machine.
A bipolar field has a hypertonic pole or centre of concentration, and a hypotonic pole or centre of dilution.