OTTO or OTHO, a German philosopher of considerable eminence, was born in 1602, and died at Hamburg in 1686. In conjunction with Torricelli, Pafchal, and Boyle, he contributed much to the farther explanation of the properties of air. He was counsellor to the elector of Brandenburg, and bur- gymaster of Magdeburg, but his greatest celebrity was derived from his philosophical discoveries, in a particular manner the invention of the air-pump. Mr Boyle indeed made approaches towards the discovery of it much about the same time, but with that candour which is ever the characteristic of great and enlightened minds, he confessed that the merit of it belonged exclusively to Guericke, the account of whose experiments first enabled him to bring his design to any thing like maturity. Our author has also the merit of inventing the two bras hemispheres, by which the pressure of the air is illustrated, and an instrument for determining the changes in the state of the atmosphere, which fell into disuse on the invention of the barometer. By consulting his tube he predicted approaching storms, on which account he was deemed a forcerer by the ignorant multitude. It is worthy of observation, that when his bras hemispheres were applied to each other, and the air exhausted, it resisted the efforts of sixteen horses to draw them asunder. He composed several treatises in natural philosophy, the principal of which is entitled Experimenta Magdeburgica, 1672, folio, which contains his experiments on a vacuum.