### Lot description at auction

Bonhams auction description

INSTRUMENTS OF SCIENCE, TECHNOLOGY AND MECHANICAL MUSIC

27 Oct 2015, 13:00 GMT

LONDON, KNIGHTSBRIDGE

http://www.bonhams.com/auctions/22832/lot/44/?category=list&length=10&page=5

A very rare silver aide-memoire for accounting and calculation, English, circa 1675, the oval plaque is engraved on the obverse with a double table. That on the left, marked 'F[orbearance] : 6.' gives simple interest at 6% (the legal rate of interest in England between 1651 and 1714), on ten thousand million over the number of days marked in the central column, forbearance being money paid to a creditor over and above the interest to allow full repayment of a loan to be deferred beyond the stipulated time. The right table marked 'D[iscount]: 6.' Gives the discounted amount required to produce the same sum in the stated number of months. The reverse is engraved with mnemonic formulae for the solution of quadratic equations 2in (5cm) x 1 1/2in (3.8cm)

Footnotes

Research by the present owner and others suggests that this handy mnemonic device is to be associated with the work of John Collins, FRS (1625-1683), mathematician and accountant. In 1669 Collins published a tract entitled Compendium for a letter Case which was posthumously re-issued in expanded form as The Doctrine of decimal Arithmetick, simple Interest & c. as also of compound Interest & Annuities, Generally performed for any time of Payment or Rate f Interest by help of a particular Table of Forbearance of it in Principal, abridged for portability in a Letter Case..., in 1685. Both these works are consonant with the present plate. So too is what Collins tells John Wallis about his work in 1667, that 'the precept for equations of payments will discover the time, when one sum at simple interest shall amount to any other proposed'. A further instance of congruity is that the table of simple interest as engraved on the plaque can also be found in Collins published works.

The engraving of the present plate shows similarity with the signed works of Hilkiah Bedford.