The Chairman, J. S. Hall asked I. P. Willams (Reading, England) to speak on ‘Planetary Formation’.

Williams: According to a theory by McCrea, published in 1960, after a protosun has been formed about 1000 unstable cloudlets, called floccules by McCrea, are captured in orbit around this protosun. Their orbital distance is roughly equal to the mean free path of the floccules in the original gas cloud from which both the sun and the captured floccules formed, taken numerically to the 60 AU. In order to conserve angular momentum about 600 of the captured floccules will be in prograde orbit while 400 will be in retrograde orbit. As an agglomeration of about 20 floccules is stable, when floccules adhere on collision stable condensations may be formed. We make a statistical investigation of this process. The problem is similar to that of having 400 red balls and 600 black balls in a bag which are pulled out and assembled into a pile. When 20 are in a pile a stable condensation exists and a new pile is started. If there are equal numbers of red and black balls in a pile this compounds to a condensation with very low angular momentum which falls into the Sun and so this is rejected and a new pile started. The number of stable condensations that is formed and the ratio of prograde to retrograde floccules in each of these condensations are obtained. This ratio determines the angular momentum, and hence the position, of the condensation.