Copy letter from Henry Power, Halifax, to William Croone Concerning some magnetical experiments, three of which he hopes they have received. Has since been tampering with the loadstone, which will advance his hypothesis 'that the effluvium of all Magneticks ......are channelled through magnetick bodies, as lighrt through a burning - glasse' Describes the experiment which he would like annexed to his former ones. Asks for Croone to send him details of Dr Wren's instrument. 24 March 1661