Letter, from Henry Oldenburg to Henry Howard Wishes to have correspondents in the major cities in Italy and suggests a number of possible names; enquiry about whether there is a person who knows about the Roman way of plastering and the creation of tools to cut porphry; wishes to understand the preparation of a certain artificial marble used at the Elector of Bavaria's palace at Munich; wishes for a specimen of mineral salt from the mines of Calabria 27 July 1666