Compound interest in the seventeenth century
Richard Witt’s Arithmeticall Questions, published in 1613, was a landmark in the history of compound interest. In a previous paper (JIA, 96) I have described the book and attempted to show why it is so important. This article sets out some information about Witt’s life, which has come to light as a result of research done since the previous article (when very little was known about him). Then follows a discussion of some of the books on compound interest which were published later in the seventeenth century. These not only help to fill in the practical background but also show how the techniques came to be more widely known and how problems arose when interest rates were reduced. It is worth noting that there was an average inflation rate of around 1% pa during the first half of the century and an average inflation rate of nil, or even a slight deflation, during the second half (Birks & Morrell, 1976; Mitchell & Deane, 1962). Thus, to a very considerable extent, the interest rates used in calculations were real rates of interest.