290 * Further Remarks on the Mode 



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, and other iron, was very remarkable 

 on a compass placed in different parts of the deck near the fore- 

 mast. [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 

 anomalv on a west or east course [Inference No. 8], the inter- 

 section of the hne joining the two situations in opposite sides of 

 the ship with the midship line traced fore and aft, will probably 

 point out a situation directly over the top of the focus of attrac- 

 tion, where no anomaly on any course whatever will appear. 



The Esk, in which I made my magnetical observations, had,^ 

 as above stated, an armourer's forge near the larboard bow, which 

 with the varying position of large quantities of iron work, com- 

 posing our whale-fishing apparatus, contributed to varythis point 

 •where no anomalv is supposed to exist, and prevented me from 

 ascertaining satisfactorily, at any time, its precise situation. I 

 made indeed but very few observations with this view, and these 

 I find neither establish nor refute the inference. 



12. The anomaly of variation is probably the greatest in men 

 of war, and in ships which contain large quantities of iron ; but 

 it exists in a very considerable degree also in merchantmen, where 

 iron forms no part of the cargo, especially in high latitudes, where 

 the dip of the needle is great. 



Whitby, 3dNov. 1818. WlUlAM ScORESBY Jun. 



XL VI I. Further Remarks on the Mode of taking Lunar Ob- 

 servations. By Mr. Henry Meikle. 



To Mr, Tilloch. 



Sir, — J.N my paper on the lunar observations, a property of the 

 ellipsis was referred to, which I suspect is hardly to be met with 

 in an elementar\ treatise, if indeed in any other work, and shall 

 therefore now give a demonstration of it in a more general pro- 

 position. 



Theorem — The normal drawn from the transverse axis of an 

 ellipsis is less than the semiaxis minor, when they do not coin- 

 cide ; but the normal produced to meet the conjugate axis is 

 greater than the semiaxis major not coinciding with it ; and the 

 normal and normal so produced are in the duplicate ratio of the 

 axes. 



Let 



