The development of astronomical knowledge has now reached a stage where a precise description of the details of star formation has become a major issue. The enormous degree of contraction that occurs in stellar condensation, a concentration sufficient to increase the density of material from, say, 10-22gr./cm.3 up to ultimate values of the order of I gm./cm.3, gives a sure indication of the important part played by gravitational forces. Apart from gravitation, gas pressure must be accorded a significant place in the early stages of the process. It has been suggested that radiation pressure should also be included among the forces that determine the onset of condensation.