In the continuing study of solar oscillation by means of optical resonant scattering1, two sets of data were obtained between June and August 1981. The first of these was at Haleakala on the island of Maui and consisted of 70 days of data over a period of 83 days, whilst at Izana on the island of Tenerife 85 days were obtained from an observing season of 88 days. At Izana a total of 895.5 h of data gave an average of 10.5 h per day, whilst on Haleakala an average of 10.1 h per day was achieved. As the two sites are ∼9.5 h apart partial overlap of data often occurred. These data represent the apparent line of sight velocity between the solar surface and the observer. It is the analysis of such data that has led to the discovery of the 160-min oscillation2, the structure and global nature of the 5-min oscillations3 and recently, the rotational splitting4 of these latter oscillations gave the first conclusive experimental evidence that the solar core is rotating more rapidly than the observable surface. The new data on solar line of sight velocity measurements reported here, establish the existence of a 13.1 ± 0.2 day (synodic) signal of amplitude 6.5 m s−1. This is variously interpreted in terms of a rapidly rotating solar core.