150 ANNUAL OF SCIENTIFIC DISCOVERT. 



VARIATION OP THE MAGNET. 



Sir J. Ross stated before the Mechanical Section of the British Associa- 

 tion, in proof of the effect of every description of light on the magnet, that, 

 during his last voyage in the Felix, when frozen in about a hundred miles 

 north of the magnetic pole, he concentrated the rays of the full moon on 

 the magnetic needle, when he found it was five degrees attracted by it. 



VARIATION OF THE COMPASS IN IRON SHIPS. 



At the last meeting of the British Association, the Rev. Dr. Scoresby 

 contributed a paper of great interest on the loss of the Tayieur, and the 

 change in the action of the compasses in iron ships. Recapitulating the 

 facts connected with the wreck of the Tayieur, which, it will be remem- 

 bered, was an iron, ship, the lecturer remarked that her compasses (three 

 adapted for guidance) were all " adjusted," previous to sailing, by large 

 and powerful magnets, on the principle suggested by the Astronomer 

 Royal ; and Mr. Grey, who had charge of the adjustment, reported that 

 they were quite correct. On the third day of the voyage it was discovered, 

 for the first time, that there was a material difference between the com- 

 passes. Judging from one of them placed near the helmsman, the captain 

 was under the impression that he was sailing down almost mid- channel, 

 or, at all events, that he was in a good position for navigating the Irish 

 Channel ; while the second showed a difference of almost two points. 

 Not knowing which of these was correct, the captain assumed, from cer- 

 tain indications he had noted, that the wheel compass was accurate rather 

 than the other. The result showed that neither was correct, and the Local 

 Marine Board of Liverpool reported to the Board of Trade their belief 

 that the wreck was caused by " a deviation of the compass, the cause of 

 which they have been unable to determine." Now, he, (Dr. Scoresby,) at 

 the meeting of the British Association at Oxford, in 1847, had called atten- 

 tion to the instability of the magnetic distribution in ships built of iron. 

 So far back as 1819 he had shown that the adjustment of the compasses of 

 iron ships by fixed permanent magnets was not only delusive, but danger- 

 ous ; and he now said, referring to the case of the Tayieur, that it was an 

 incidental (for he did not contend that it was a necessary) consequence of 

 such an adjustment in this case that the vessel had been brought into so 

 dangerous a position. If the compasses had not been corrected by perma- 

 nent magnets, the captain would have been in a very different position for 

 securing the safety of the ship. It was a matter well known, not only 

 that iron became magnetic by virtue of the inductive influence of the 

 earth, but that magnetism might be controlled, altered, or destroyed by 

 mechanical action. An iron bar, entirely neutral as to its molecular mag- 

 netism, as shown by its being devoid of influence when placed horizontally 

 in an east and west line near a compass, became strongly magnetic when 



