Unpublished manuscript, 'On the construction and use of a magnetic balance' by William Snow Harris Harris writes about his design for a magnetic balance used to investigate the properties of natural and artificial magnets and to allow for a simple way of observing the action of one magnet upon another or upon a non-magnetic substance. Harris includes tables of data from his experiments with the magnetic balance. A covering page includes an ink inscription reading 'JFHW [John Frederick William Herschel] (No. 77) Mr Harris on the Magnetic Balance' and below, in graphite in another hand, '1825 Archives - unpub / tear off blanks'. Corrections and deletions appear throughout in ink. On verso of page ten are calculations by Herschel testing the conditions of possibility of Harris' balance. Subject: Scientific Instruments / Physics Written by Harris in Plymouth [Devon, England]. 29 May 1825