Rahn, Johann Heinrich (1622-1676).

first edition, and an uncommon book. In this book Rahn introduced the symbol ÷ for division ('Das Haubtzeichen des Dividierens ist ÷', p. 8). This is actually a use devised by John Pell. For multiplication Rahn used the asterisk (pp. 7-8). He also uses the sign @ [reversed] ('Das Haubtzeichen des Involvierens') and omega ('Das Haubtzeichen des Evolvierens'). Although not new (the ÷ symbol had previously been used as a critical mark to obelize text considered dubious or corrupt), this was its first mathematical application. Rahn also set out equations in three columns (two for identification, one for explanation), again something derived from Pell (see below). 

Rahn belonged to an important Zurich family, and his father was Bürgermeister there from 1655 to 1669. J.H. Rahn was involved in the military life of the town and seems to have got to know the Englishman John Pell, who was the representative of the Commonwealth there, by about 1654. By 1657 he was going to Pell for tutorials in mathematics every Friday night after Pell 'had writt his post-letteres' (Aubrey, quoted by N. Malcolm, p. 164). Early 1658 saw Rahn installed as provincial governor of Kyburg, an area in the northern part of the canton of Zurich, where his official duties allowed him little time for mathematics. However he did find time to write this work, which is in fact heavily indebted to Pell, who is mentioned, although not by name ('die ich von einer hohen und sehr gelehrten person erstmals erlehnet hab...') with particular reference to the system of working out a problem in three columns. The division sign we have already mentioned, but also Rahn included Pell's theorem on squaring the circle, which had been in his Controversiae pars prima.

Pell's career is fully described in the recent work by Noel Malcolm and Jacqueline Stedall (see lot 1706).