192 



unloading the cargo thej were all discovered alive and healthy, except 

 in one or two cases where they had been crushed between packages. 

 From the number found, it would appear that all bad changed their 

 ekins, and many were found perfect. 



The following paper was read, — • 



OX THE DEVIATION OF THE COMPASS 



ON BOARD IRON STEAMERS PROCEEDING TO THE 



SOUTHERN HEMISPHERE, 



By J. T. TowsoN, Esq. 



The term " Deviation of the Compass " is now employed to indicate 

 the error of the compass resulting from the attraction of the iron of 

 the ship, either employed in her construction, in her equipment, or in 

 her cargo. 



Variation, on the other hand, is the term applied exclusively to that 

 error of the compass arising from the fact of the magnetic poles of the 

 earth not being identical with the poles on which our planet performs 

 her diurnal motion. 



It is the former of these errors of the compass to which we shall 

 refer in this paper. 



It is admitted " that ships have been, and still are, navigated across 

 the seas by persons who have no knowledge of the deviation of the 

 compass;" but this is no argument against the attention of the 

 navigator and the shipowner being directed to this subject. We do not 

 pretend that the greater number of wrecks that are hourly occurring 

 result from the neglect of the consideration of this subject ; but we 

 could occupy the whole of the time which it would be prudent to devote 

 to the consideration of this subject, in detailing the various calamities 

 which have resulted from the general neglect of a due consideration of 

 this eiTor. We further maintain, that there was never a period in the 

 history of navigation in which its consideration was equally demanded 

 as in the present ; and that there does not exist a community more calcu- 

 lated to be affected by the phenomenon under our consideration than 

 that of the mercantile body of Liverpool. 



In order to understand the nature of the deviation of the compass, it 

 is necessary to comprehend some portion of the theory of magnetism. 

 The theory of magnetism, as a whole, is, however, too extensive a 

 subject to occupy our attention in connection with the present investi- 

 gation. We may, therefore, be pardoned in selecting those branches of 

 the science that are in any measure connected with the mariners 

 compass. We would observe that a magnet is a body (generally 



