On the proper motion of small pores in sunspot groups

The possibility of measuring pore positions and proper motions with high accuracy, using time series of short exposure photographs, is discussed. Preliminary measurements of a series covering a time span of 110 min. show that positions of small pores may be defined, and horizontal velocities determined, to within 0.1, or 30 m s^–1, respectively.Mitteilungen aus dem Kiepenheuer-Institut No. 173.