14 Transactions. — Miscellaneous. 



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 sach 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., Yol. Y., p. 128), and, 

 although I agree to a very great extent with his remarks, I am inclined to 

 think that the sraallness 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 2:)osition 

 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. lY) 



\^Reacl before the Wellington Philosophical Society, I3th October, 1S73.] 

 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 i-aised) 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 



