x PRACTICAL PURPOSE 273 



extensive building of iron ships. Though some acknow- 

 ledgment of an important service thus rendered to 

 navigation might have been expected, the Admiralty 

 refused to sanction any reward for it ; possibly because 

 the Government did not then possess a single iron vessel 

 and was not disposed to urge the inquiry into the effect 

 of a ship's magnetism upon the compasses. When Airy 

 commenced the investigation, the whole subject was in 

 darkness, yet by the application of a mechanical theory 

 he brought it under control. Lord Kelvin made a great 

 advance later by the use of short needles for the compass 

 cards, but the method of correcting the compasses in 

 iron ships, now adopted not only in the merchant 

 service but also in the navies of all countries, is that 

 worked out by Sir George Airy in 1839. Airy mathe- 

 matician and astronomer has thus been justly called 

 the father of the mode of mechanical compensation of 

 the compass now followed throughout the civilised 

 world. 



Neither Airy nor Kelvin had any special knowledge 

 of ships' compasses when they took up the problems 

 which they solved with such complete success, but they 

 knew that the best way to attain a practical purpose 

 is to submit the conditions to scientific analysis before 

 devising arrangements to meet them. This method 

 may be tedious, but it is always the best in the end. No 

 matter to what branch of human activity the subject 

 belongs, the preliminary scientific investigation under- 

 taken with the view of understanding it fully makes 

 the surest foundation of advance. All work which 

 has not this basis is of the empirical, trial and error, rule 

 of thumb, kind ; it is a shot in the dark, and though the 

 target may be hit the chances are very much against it. 

 When science is brought to bear upon a practical problem, 



G.D. 



