Mr. John Gray, of Liverpool, has published a letter, in which he proves, by the example oftheSa'rahSands,that the compass can be as accurately adjusted in iron vessels as in those of wood. He says:—This steamship has been a most valuable agent for the determination of a mooted point now being investigated, whether iron ships undergo a very important change alter crossing the Equator or not. For years I have entertained the opinion thafy for all practical purposes, the adjustment on Profesior Airy's principle- will answer equally well in both north and south latitudes, and which this vessel has demonstrated beyond all doubt. Simultaneous bearings were taken by Captain Thompson, and his chief-officers, in various parts of the Straits of Magellan, a_nd the result clearly showed that no deviation whatever took place.