deviation by changing the proportion of the ship's sub-permanent magnetism to the terrestrial-horizontal magnetism, upon which proportion the compass deviation depends), it gratuitously introduces a class of errors which are entirely avoided by correcting the compasses by magnets and soft iron. The changes which occur in the magnetism of a ship sailing from one hemisphere to another, say from the Clyde to Port Chalmers (the difference of magnetic latitude being somewhere about 100 degrees), cannot take place in vessels traversing ten or twenty degrees in one hemisphere only; in fact, I believe that if one of our intercolonial steamers had the compasses on board accurately adjusted in a New Zealand port, by means of magnets and soft iron, the deviation from such changes as those to which I have alluded would be almost, if not altogether, imperceptible in a voyage to or from Melbourne. I have perused with great pleasure the paper by Captain Edwin in the last volume of the “Transactions” (Trans. N.Z. Inst., Vol. V., p. 128), and, although I agree to a very great extent with his remarks, I am inclined to think that the smallness of the magnetic disturbance in the “Luna” is not so much owing to that vessel having been built of steel, as to the fact of her having wooden bulwarks and the very careful manner in which the position of her compass has been selected; and I think it probable that the difference in deviation observed on board that vessel between Auckland and the Bluff might be altogether eliminated by means of soft iron alone.

Art. III.—Description of the Patent Slip at Evans Bay, Wellington, and of the Mode of Erecting or Constructing the same. By J. Rees George, C.E. (PI. IV.) [Read before the Wellington Philosophical Society, 13th October, 1873.] The slip consists of a set of ways, upon which is placed a carriage or cradle running on wheels. The carriage is constructed suitably for hauling up or lowering away ships, motion being given to it by means of a winch or set of geared wheels, hauling-up and lowering-down chains being attached thereto; and the whole is set in motion by means of two 25 horse-power horizontal high-pressure steam engines, placed in position for the purpose. The ways or rails are manufactured of cast iron. The centre way (which bears the greater portion of the weight of a vessel when being raised) is of the section of two ordinary E girders, connected together at their top tables and other points, two rails 2 ft. 6 in. apart from centre to centre being cast on the top, and two racks to take the palls as a vessel is being hauled up to