Letter, regarding observations of the tides of the River Thames [London] using the marine surveyor from Henry de Saumarez to Isaac Newton and the Royal Society De Saumarez describes the use of an instrument called the marine surveyor and gives details of experiments made with it on the River Thames in order to determine the strength of the tides of flow and ebb. Subject: Scientific apparatus and instruments / Oceanography Published in Philosophical Transactions as 'Observations upon the tides in the River Thames, by Mr. Henry de Saumarez' 8 December 1725