Abstract: Improved magnetic stirring means for use with an optical absorption cell of the type characterized by a non-magnetic container for fluidic samples to be analyzed, which container has a rectangular cross-section of interior dimensions A .times. B, where A is relatively large compared with B. The stirrer comprises a magnetically responsive body positioned at the bottom of the container, for effecting agitation of the sample in response to a rotating magnetic field applied by field sources which rotate about a vertical axis beneath the container. The stirrer body is of generally cylindrical cross-section, of axial length slightly less than the dimension A, and of diameter slightly less than dimension B. The stirrer body is oriented with its axis in a horizontal plane, and thus its lateral periphery lies closely adjacent to the internal container walls. The body carries permanent magnet means toward one end thereof, which provide a pair of opposite magnetic poles displaced to alternate sides of the body axis.