379 



deviation to the eastward, and in the latter to the westward, of the 

 true magnetic meridian. 



Considering the height of the general mass of iron in the vessel 

 and also that of the head and stern, together with the distance (169 

 feet) at which some of the needles indicated a deviation, the author 

 'concludes that the respective deflections were caused by the magnetic 

 influence of the iron in the vessel the combined effect of that about 

 the bows representing the north pole of a magnet, and that about 

 the stern a south pole. He then offers several suggestions for future 

 observation on this subject, and connected with the little oxidation 

 that is reported to have taken place in the vessel. 



The experiments having been interrupted by a continuance of wet 

 and stormy weather, the author proceeds to draw the following gene- 

 ral practical conclusions, deduced from the series of observations 

 already made, and points out the further experiments which he con- 

 siders necessary to be tried. 



1st. The ordinary place for a steering-compass on board ship is 

 not a proper position for it in an iron steam-vessel. 



2nd. The binnacle-compass in its usual place on board the Garry- 

 owen is too much in error to be depended upon. 



3rd. In selecting a proper position for a steering-compass onboard 

 iron steam-vessels, attention should be paid to its being placed, as 

 far as is practicable, not only above the general mass of iron, but also 

 above any smaller portions of iron that may be in its vicinity; or such 

 portions of iron should be removed altogether. 



4th. The steering-compass should never be placed on a level with 

 the ends either of horizontal or of perpendicular bars of iron. 



5th. The extreme ends of an iron vessel are unfavourable positions, 

 in consequence of magnetic influences exerted in those situations. 

 The centre of the vessel is also very objectionable, owing to the con- 

 necting rods, shafts, and other parts of the machinery belonging to 

 the steam-engine and wheels, which are in continual motion ; inde- 

 pendently of the influence exerted by the great iron tunnel in this 

 part of the ship. 



6th. No favourable results were obtained by placing the compass 

 either below the deck, or on a stage over the stern. 



7th. It was found that at a position 20^ feet above the quarter- 

 deck, and at another 13^ feet above the same level, and about one 

 seventh the length of the vessel from the stern, the deflections of the 

 horizontal needle were less than those which have been observed in 

 some of His Majesty's ships. 



The author proceeds to point out various methods of determining, 

 by means of a more extended inquiry, whether the position above 

 indicated, or one nearer to the deck, is that at which the steering- 

 compass would be most advantageously placed. 



The concluding section contains an account of some observations 

 made by the author on the effects of local attraction on board dif- 

 ferent steam-boats, from which it appears that the influence of this 

 cause of deviation is more considerable than has been generally ima- 



