Page:Life of Sir William Petty 1623 – 1687.djvu/132

 Spragge, to fix an engine with propelling power in a ship, and with devising a new rigging. But the subject which claimed his special devotion was naval architecture, and more particularly the construction of a sluice-boat, or 'double bottomed ship,' for the easier navigation of the Irish Channel.

On November 27, 1665, after communicating to the Royal Society a paper on the 'History of Clothing,' Sir William read his general views on the subject of 'Shipping.' His mature opinions were finally set out in a 'Treatise or Discourse about the Building of Shippes, presented in MS. to the Royal Society;' which 'William, Lord Brouncker, President of the Council pertaining to that Society, took away,' says Aubrey, 'and kept in his possession till 1682, after saying it was too great an arcanum of State to be commonly perused.'

The 'sluice-boat,' or 'double bottom,' to quote the names by which the experiment is described, was, correctly speaking, a ship with two keels joined together by transverse connections, and resembled the vessel known as the 'Calais-Douvres,' which in recent years was successfully used for the improved navigation of the English Channel, until superseded by still more perfect designs. On November 12 and November 19, 1662, Sir William addressed two communications to the Royal Society, concerning 'a double bottomed cylyndrical vessel;' and Captain Graunt was desired to inform the Doctor that 'the society was well pleased with the idea, and that the members of the society in Ireland be appointed a committee on the matter.' Evelyn says of this invention: 'The vessel was flat-bottomed; of exceeding use to put into shallow parts, and ride over small depths of water. It consisted of two distinct keeles, crampt together with huge timbers; so as a violent stream ran between them. It bore a monstrous broad saile.'