Plate, 'Curves of the diurnal deviations of a magnetic needle whose directive power was diminished by the action of two bar magnets placed in the line of the dip: the N end of the needle pointing north' by Samuel Hunter Christie Chart showing the diurnal deviations of the magnetic needle. Subject: Magnetism / Navigation Published in Philosophical Transactions as 'On the diurnal deviations of the horizontal needle when under the influence of magnets'. Communicated by Sir H [Humphry] Davy. Read 19 June 1823. [1823]