The Coulter Counter was created by Wallace H. Coulter in 1949. The Coulter counter consists of two electrolyte reservoirs that are connected by a small channel, through which a current of ions flow.  Each particle drawn through the channel causes a brief change to the electrical resistance of the liquid. The change in the electrical resistance causes a disturbance in the electric field. The counter detects these changes in electrical resistance; the size of the particles in the field is proportional to magnitude of the disturbance in the electric field.