1869.] 



Iron-built Sailing-ship ' Glenorchy.' 



41L 



From these I derive the following expression for the deviation (S) in 

 terms of the azimuth of the ship's head (£) measured eastward from the 

 magnetic N. 



3 = 30' + 30' sin £+ 1° 2' cos £ + 2° 37' sin 2£-38' cos 2£. 



These values show that the semicircular deviation had been entirely 

 corrected. Of the quadrantal deviation a small part appears to have been 

 uncorrected. There are practical difficulties in the way of correcting very 

 large amounts of this deviation by soft iron, and I have no doubt Mr. 

 Fleming acted with judgment in not attempting to carry this correction 

 further. We may probably assume the maximum quadrantal deviation 

 to have been about 10°. 



The standard compass was not corrected by magnets, but its deviations 

 were observed, and a Table of the deviations furnished. They were : — 



e Glenorchy' Standard Compass, December 18, 1868. 



Magnetic Course. 



Deviation. 



Magnetic Course. 



Deviation. 



N. 



+ 12° 



S. 



- 5° 



N.N.E. 



- 7 30' 



S.S.W. 



+ 7 30' 



N.E. 



-24 



s.w. 



4-16 



E.N.E. 



-37 30 



w.s.w. 



+22 30 



E. 



-38 



w. 



+33 



E.S.E. 



-31 30 



W.N.W. 



+35 30 



S.E. 



-24 



N.W. 



+35 



S.S.E. 



-11 30 



N.N.W. 



+20 30 



These values give 



a=0, 23 = --610, £= + '105, 50= +.100, e = 0. 



This Table and these values do not bear directly on the loss of the ship, 

 because owing, as I collect, to the unsteadiness of the pillar the standard 

 compass was found to be useless, and the ship was navigated by the 

 steering-compass alone ; but it is interesting from the light it throws on 

 the general magnetic character of the ship, and its confirmation of the 

 results obtained from the steering-compass. 



The proportion of C to — 13 exactly agrees with what we know of the 

 direction in which the ship was built. 



The large value of — 13 was no doubt owing to the original magnetism 

 of the hull and not to the iron cargo, which in fact probably rather 

 diminished than increased the — 13. 



Cards containing the deviations of both compasses were furnished to the 

 captain. 



The question of the correction of the standard compass by magnets is 

 one which has become of so much importance that I may be pardoned for 

 interposing a digression on this subject and for inserting a passage from 

 the third edition of the 'Admiralty Manual' now in the press. 



