An iterative technique for the rectification of observed distributions

J q,•.=I:Pi,Vt;, i-I f "'(~)d~=1 and "'W~O of the variation of star density along a line-of-sight from the distribution of proper motions in that direction; (2) the determination of the space distribution of radio sources from number counts; (3) the determination of the radial variation of star density in a globular cluster from star counts; (4) the correction of radioastronomical and spectrographic observations for the effect of the instrumental profile; and (5) the determination of the temperature stratification in the solar atmosphere from limb-darkening data. These examples suffice to show that the problem under consideration arises in many branches of astronomy and that its solution is vital to the process of extracting useful information from observations.