An instrument similar to the konimeter but differing in that the air to be sampled undergoes humidification prior to being blown through the jet. The velocity of impingement is about 200 to 300 m/s and the jet is rectangular instead of circular. The prior humidification of the air causes condensation of moisture upon the dust particles by super saturation due to the pressure drop at the jet, and so assists in the deposition and retention of the particles on the slide. The Bausch and Lomb dust counter is the American counterpart of this instrument.