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Thanks to William Poole for his useful review (Books, 24 April) of Notebooks, English Virtuosi, and Early Modern Science by Richard Yeo.

I now realise that Thomas Harrison¡¯s arca studiorum, ¡°a kind of filing cabinet in which different pieces of paper could be shuffled between various hooks¡±, was a precursor of the Paramount card index system that some of us tried to use before the advent of electronic databases. Developed by the Copeland-Chatterson Company it consisted of cards with holes punched around the edges, a long ¡°knitting needle¡± and a clipper. A particular topic was assigned to each hole. Whence, bibliographic references could be written on the cards and classified by clipping the appropriate hole. The needle was then passed through a chosen hole, the suspended cards shaken and the clipped cards in the specified category would nicely fall out. Or that was the theory. In practice cards somehow adhered together or scattered all over the floor, and the long needle was a risk to your immediate neighbour if used in a library.

R. E. Rawles
Honorary research fellow in psychology
University College London