The roots of this study lie deep in the past: I have been interested in the history of the early Royal Society ever since, in 1951, I was generously allowed by the Society's then President, Council and Librarians to plunge into a study of the Boyle papers, the first to wish to do so, probably, since the mid-eighteenth century. This interest has grown with the years, especially when, some ten years later, my husband and I began to edit the correspondence of Henry Oldenburg, named as one of the two Secretaries in the Charters of 1662 and 1663. In those days historical interest in the Royal Society centred mainly on the Society's origins, while currently it is rather on its institutional aspects and its sociological roots. Very little attention has been given, even now, to exactly what went on at its meetings, and especially what its Curators and Operators did in return for their salaries and what they contributed to its meetings, then its main activity. In the twentieth century, as in the seventeenth and eighteenth, many, perhaps most, Fellows value the Society principally for the honour which election to it confers, only a minority taking an active röle in its administrative affairs. But for those seventeenth-century Fellows who best exemplified the Society's aims, it was participation in the meetings which counted, and hence what went on at those meetings reveals much about their interests and those of the Society as a whole. For reasons which will become apparent below, I chose to concentrate upon one aspect of the Society's work, namely its concern with experiment.