MARINE Chair, a machine invented by Mr Irwin for viewing the satellites of Jupiter at sea, and of course course determining the longitude by their eclipses. An account of it is given in the Journal Estranger for March 1760. An account of its accuracy was published in the year following by M. de l'Isle astronomer in the Imperial academy of Petersburgh; but notwithstanding the encomiums bestowed upon it by this gentleman, it hath never come into general use; and therefore we may conclude, that it is much inferior to the inventions of Mr Harrison for the same purpose. See HARRISON and LONGITUDE.

MARINE SURVEYOR, is the name of a machine contrived by Mr H. de Sanmarez for measuring the way of a ship in the sea. This machine is in the form of the letter Y, and is made of iron, or any other metal. At each end of the lines which constitute the angle or upper part of that letter, are two pallets, not much unlike the figure of the log; one of which falls in the same proportion as the other rises. The falling or pendent pallet meeting a resistance from the water, as the ship moves, has by that means a circular motion under water, which is faster or slower according as the vessel moves. This motion is communicated to a dial within the ship, by means of a rope fastened to the tail of the Y, and carried to the dial. The motion being thus communicated to the dial, which has a bell in it, it strikes exactly the number of geometrical paces, milcs, or leagues, which the ship has run. Thus the ship's distance is ascertained; and the forces of tides and currents may also be discovered by this instrument: which, however, has been very little used.