55^ MAGNETICAL OBSERVATIONS. [aPI*. n" IX. 



upon the dmm-licad of the capstern, anywhere out of 

 the centre, will have its north point so forcibly attract- 

 ed by the upper end or south pole of the spindle, 

 that the ship's head may be made to appear to be 

 directed to any point whatever, at the pleasure of the 

 experimenter. I liave sometimes excited the astonish- 

 ment of my officers by taking the binnacle compass, 

 and so placing it on the capstern-head, that the ship 

 has appeared to be steering a course directly contrary 

 to that intended. 



10. When the iron in a ship is pretty equally distributed 

 throughout both sides, so that the focus of attraction occurs 

 in midships, a compass placed on the midship line of the deck, 

 (drawn longitudinally) will be free from any anomaly from 

 one end of the ship to the other, when the course is north or 

 south ; but on every other course an anomaly will generally 

 appear, increasing as the angle between the ship's head and 

 the magnetic meridian increases, until the error is at a maxi- 

 mum, when the course is east or west. 



a. The unequal distribution of iron in the ship, on board 

 of which I made all my experiments, prevented the 

 above effect from being realized. A blacksmith's shop 

 was situated between decks, on the larboard side of 

 the fore-hatchway. It was lined with sheet-iron ; and 

 besides the armourer's forge, vice, &c. contained a large 

 quantity of other iron. The effect of this, together 

 with the anchors, windlass-necks, &c. was very re- 

 markable on a compass placed in different parts of 

 the deck near the foremast. (See Observations 18, 

 19, and 20. of the prefixed Table.) 



11. As a compass placed on the midship line of the deck is 

 subject to no anomaly fore and aft, in certain ships, on a north 

 or south course (Inference No. 10), and as a compass in either 

 side of the ship, opposite to the focus of attraction, shows no 

 anomaly on a west or east course (Inference No. 8), the inter- 



