272 DISCOVERY CH. 



The problem presented by the use of iron in ships 

 was definite but complicated ; and it could be solved 

 only by scientific investigation. Mr. Archibald Smith, 

 a Chancery barrister who devoted all his leisure hours 

 to the application of mathematics to navigation, had 

 this practical purpose in mind ; and his work was recog- 

 nised by the award to him, in 1872, of a gift of 2,000 

 " for the long and valuable services which he had 

 gratuitously rendered to naval science in connection 

 with the magnetism of iron ships, and the deviation of 

 their compasses." The chief credit must, however, be 

 given to Sir George Airy, the Astronomer Royal, who, 

 in 1838, was asked to undertake experiments on a ship 

 the Rainbow for the purpose of discovering a correction 

 for the deviation of the compass produced by the iron 

 of which it was constructed. The deviation was so 

 great that the compass of the ship was as much as fifty 

 degrees out of the magnetic north and south direction. 



Airy investigated the subject theoretically as well as 

 practically, and calculated the strength of the magnetic 

 action required to counteract the disturbance. In a 

 month he had completed his inquiry. He took the 

 necessary compensating magnets and iron correctors 

 to Deptford, where the ship was lying, mounted them 

 in their proper places, tried the ship, and the compass 

 was then found to be sensibly correct. In the same 

 year, another iron ship the Ironsides built at Liver- 

 pool, had her compass similarly corrected by Airy ; 

 and in this case, as in the Rainbow, the disturbance 

 was so great as to make the vessel worthless without a 

 mechanical means of correcting the effect due to the 

 iron. 



The success of the methods employed for the correction 

 soon became widely known, and led immediately to 



