THE MOST CURIOUS CRAFT AFLOAT 



241 



tion of a competent sailing master was 

 "turned down" solely because of his 

 "iron" constitution, and that we allowed 

 only "bronzed" sailors on board the 

 Carnegie! 



But, zcliy was if iieeessary to build a 

 vessel practically leithoat iron, and just 

 what is the adz'antage in disco-rcring 

 chart errors leith Jicr? 



As the reporter correctly says : 

 "There is only one non-magnetic ves- 

 sel afloat, and that is the Carnegie, and 

 the magnetic vessels seem to have got 

 along very well in spite of errors." 



KFFECT OF SHIP's IRON ON THE COMPASS 



The iron on board a vessel affects the 

 compass needle generally in the follow- 

 ing two ways : First, it disturbs and 

 alters the normal direction of the needle 

 and hence introduces the error known as 

 the "deviation of the compass" ; secondly, 

 it weakens the component of the earth's 

 magnetic force acting on the compass. 

 Both effects require to be considered ; 

 they are neither of them constant, but 

 vary from place to place. They depend 

 upon the ship's course and change with 

 every alteration in the ship's own mag- 

 netism, due to variable cargo and other 

 causes. Even the continuous impact of 

 waves on an iron vessel has an appreci- 

 able tendency to "set" or "unset" the 

 lines of magnetic force in the vessel and 

 thus produce a change in the deviation 

 error. 



To overcome the baneful effects of an 

 iron vessel on a compass, the latter is 

 "adjusted" — that is, other pieces of iron 

 and magnets are placed in the vicinity of 

 the compass in such a way as to exert 

 an equal and opposite effect to that of 

 the ship's own iron and magnetism. To 

 make this "adjustment" it is necessary 

 to know first how the compass would 

 point were it mounted on a vessel with 

 no iron whatever in her — /. e., on a 

 non-magnetic vessel like the Carnegie. 

 AAHiether a thing is wrong, and, if so, 

 how much it is wrong, cannot be told 

 until one knows what is correct. 



To determine the size and strength of 

 the compensating magnets it does not 



suffice to know merely the correct com- 

 pass direction at the port of embarkation ; 

 the dip of the magnetic needle and the 

 strength of the earth's magnetic force 

 must also be known. Suppose that after 

 various trials the adjuster has succeeded 

 in "correcting" the compass, so that it 

 points just as it would have done in the 

 first place had there been no iron or steel 

 in the ship. Starting off on a trans- 

 Atlantic voyage, we soon find that our 

 compass has not remained "put," but, 

 instead, again shows "deviations" from 

 the magnetic north, due to some of the 

 many possible causes already mentioned. 

 What does the mariner do? When- 

 ever the sun or a star is visible he makes 

 an "observation" and finds how his dis- 

 turbed compass is pointing. Thus, for 

 example, in latitude 43°. 8 north, longi- 

 tude 58°. 9 west, the north end of his 

 compass, shows 25° west of north. 

 Turning to his charts, he learns that, 

 according to the British Admiralty Chart, 

 the bearing or "westerly variation of the 

 compass" should be 22°. 2; according to 

 the U. S. Hydrographic Office, 23°, and 

 by the German Admiralty Chart, 22°.4. 

 Taking the average of the three best 

 charts now in actual use, he finds that, 

 where his ship is. the compass should 

 stand 223^2° west, but he actually found 

 25° west; hence, assuming the charts to 

 be absolutely' correct, he concludes that 

 the deviation error of his compass at that 

 place is 2^° west for a particular head- 

 ing of ship. And, if he is a cautious 

 captain, he will embrace every chance to 

 "check up" when astronomical observa- 

 tions are possible. 



IMPORTANT ERRORS ON CURRENT CHARTS 

 CORRECTED BY THE "caRNEGIE" 



But we. on the Carnegie, having no 

 effect from iron to contend with, found, 

 on September 22. 1909, that in 43°.8 

 north and 58°. 9 west, the compass actu- 

 ally pointed 23°. 7 west. If the mariner 

 had known of this correct value he would 

 have found as the deviation error of his 

 compass i°.3 west instead of 2^/2° west. 

 I have taken a favorable case ; greater 

 differences between the actual and the 



