Letter, from Henry Justel to Henry Oldenburg States that he will be receiving a penknife from Germany, which is partly made from gold and iron, with a treatise on how to make it; notices from Tittel in Leipzig eg. his machine for making parabolic lenses has not been successful, that he knows how to liquify amber; concerning his mathemathical instrument which can solve geometrical and arithmetical propositions without using a compass 28 August 1675