48 Analyses of Boohs. [Jan| 



] 1 . Asa compass placed on the midship hne of the deck is 

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

 and south course ; and as a compass on either side of the ship 

 opposite to the focus of attraction shows no anomaly on a west 

 or east course, the intersection of the line joining the two situa- 

 tions 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 attraction, when no anomaly in any course 

 ■whatever will appear. 



12. .The anomaly of variation is probably greater 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. 



VII. On the Genus OcyUwe ; being an Extract of a Letter 

 from Thoivns Saij, Esq. of Philadelphia, to William Elford 

 'Leach, M.D.F.li.S. 



This paper gives a description of a fine species of ocythoe 

 found in the stomach of a dolphin, which ihe author considers as 

 new, and distinguishes by the name of ocythoe punctata. He is 

 of opinion that the ocythoe is a parasitical animal, because the 

 shell in which it is found is not closely adapted to its body, as is 

 the case with the shells of all known shell fish. 



VIII. On Lrcgularities observed in the Direction of the Com- 

 pass Needles of his Majesty's Ships Isabella and Alexander, in 

 their late Voyage of Discovery, and caused by the Attraction of 

 the Iron contained in the Ships. By Capt. Edward Sabine, of 

 the Royal Regiment of Artillery, F.R.S. &c. 



Mr. Wales, astronomer to Capt. Cook in his second voyage, 

 Vv'as the first person whose observations led to -the inference that 

 the anomalies observed on ship-board in the position of the 

 compass, were not owing to imperfections in the azimuth com- 

 pass, as had been supposed, but to the effect of the iron in the 

 ship upon the needle. This subject was afterwards investigated 

 •with much acuteness and industry by Capt. Ij'linders during his 

 survey of the coast of New Holland. He succeeded in being 

 able to apply a correction in his own ship. After his return, he 

 was permitted by the Lords of the Admiralty to prosecute the 

 investigation stiH further by trying the irregularities in different 

 ships in various harbours. Capt. Flinders published a short 

 paper on the subject in the Philosophical Transactions, and a 

 more detailed statement in the second appendix to his Voyage 

 to Terra Australis. There are three points in his statement 

 chiefly worthy of attention from their practical importance. 

 Capt. Sabine's object in this paper is to point out how far Capt. 

 FUnders's observations have been confirmed by those mac^ in 

 the Isafeella and Alexander, 

 First^ Capt. Flinders fonad that in every ship a compass 



