532 
APPENDIX. 
[ Errors in variation. 
found roughly by the bearing of two well -defined heads or points set in a 
line from opposite directions. If, after the proper corrections are made 
according to the ship’s head, the bearing be not the same, the difference 
will be seen. 
These memoranda are mostly relative to a compass fixed on the bin- 
nacle ; but the trouble of correction may be saved if a place can be found 
near the taffrel, where the attraction of the iron at the stern will counteract, 
by its greater vicinity, the more powerful attraction in the centre and fore 
parts of the ship ; and should the after attraction be too weak, it may be in- 
creased by fixing one or more upright stanchions or bars of iron in the 
stern. If a neutral station can be found or made, exactly amidships, and of a 
convenient height for taking azimuths and bearings, let a stand be there set 
up for the compass ; and if the stand must of necessity be moveable, make 
permanent marks, that the exact place and elevation may always be 
known. Observations taken here should never undergo any change from 
altering the direction of the ship’s head, at any dip of t he needle ; but it 
will be proper to verify occasionally, and to compare the azimuths and 
bearings with others taken on the binnacle. The course should also be 
marked from this compass, though the ship be steered by one before the 
wheel ; a quarter or half point being allowed to the right or left, accord- 
ing as the two may be found to differ. 
These precautions are not intended to supersede the taking of angles 
with a sextant or circle, from the sun to any chosen object, and from thence 
to others ; but in using the compass on ship-board such are those I would 
employ, in order to arrive at the true variation and to know wliat should be 
allowed on each set of bearings. In surveying with a theodolite or circum- 
ferentor on shore, my memorandum is, — To observe azimuths with the 
same instrument, and in the same spot where each set of bearings is taken ; 
unless where the back bearing can be had of some former station or of the 
ship, w here the variation has been observed. 
Had I been more early aware of the necessity of these precautions in 
the use of the magnetic needle, both on ship-board and on shore, much 
perplexing labour would have been saved ; and although every existing 
datum has been employed to remedy the deficiences, the charts which ac- 
company this work would then have presented a more correct delineation 
of the coasts of Terra Australis. 
