In 1961 a clear ocean of scientific research seemed to have opened up, ready to sail into and explore. The climate seemed set fair too. This optimism – fearing ‘nor sea rising, nor sky clouding’ – was justified by events: the 1960s proved to be a decade of fairly easy achievement, exploiting techniques already devised.

The RAE research on the upper atmosphere had so far been received in deafening silence by the Meteorological Office, which regarded anything at heights above about 20 km as rather ‘way out’ and of no interest to weather forecasters. This hardline attitude by meteorologists was slowly softening, and the Royal Meteorological Society invited me to give the Symons Memorial Lecture on 1 March 1961: the title was ‘Satellites and the Earth's outer atmosphere’, and I ranged more widely than in previous talks, discussing the history of ideas on the atmosphere and also venturing further outwards, above 1000 km height, into the exosphere and magnetosphere.

A month later came the most important scientific meeting I ever attended, the 1961 COSPAR Symposium at Florence. For this occasion we gathered all the data on air density for an updated picture of the variations with height, with solar activity and between day and night. Fig. 4.1 shows the graph of density versus height obtained from twenty-nine different satellites launched before 1961, as presented at Florence.