Cloud seeding was conducted in the Wirnmera-Mallee during the months of August, September and October 1966 and claims have been made and publicised that the wheat yield in the seeded area was increased significantly as a direct result. The claims have been investigated here by comparing rainfalls in the seeded or 'target' area with those of an unseeded 'control' area: Two types of tests were employed, the first being distribution free, and the second was based on the assumption of Normality of the relevant distributions. The same data were used in each and so obviously the tests were not independent. The results showed a rather remarkable uniformity of rainfall anomaly over the target and control areas for the seeded period. This uniformity was highlighted by the fact that the 1966 value of the ratio of target to control rainfalls was located at the median of the relevant 42 term series. From this evidence it would appear there is no justification for claims that rainfall has been affected by the cloud seeding. However, the additional point has been brought out that because the rainfall has such large inherent variability, it appears to be practically impossible to substantiate such claims based on a test sample of only one member, that is on only one set of seeded data.
G. O'Mahony (Fri,) studied this question.