Page:A Voyage to Terra Australis Volume 2.djvu/535

occurred whilst beating along that part of the south coast of Terra Australis discovered by the French, where the dip is nearly 67°; and that it may be seen how near the bearings coincided with the azimuths and amplitudes, the differences which should result from the common multiplier and sines of the angles are added to the table.

 

Objects set.	Before tacking.			After tacking.				Increase of E. Var.
	Bearings.		Ship's Head.	Bearings.		Ship's Head.		From Bearings	From Multipl.
C. Jaffa, outer part	N.  4°	W.	E.S.E.	N.  9°	W.	S.W. by W.	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$	6° 30′	5° 53′
C. Lannes, the point	S. 32	E.	——	S. 40	E.	——
Hummock	N. 35½	E.	S.E. by E.	N. 33½	E.	S.W. by W.	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$	5   0	5  34
Furthest extreme	S. 36	E.	——	S. 44	E.	——
C. Lannes, north extreme	N. 39	E	S.E by E.	N. 30	E.	West.	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$	6  30	6   8
Furthest extreme	S. 51	E.	——	S. 55	E.	——
C. Lannes, western part	N. 15	W.	E.N.E.	N. 21	W.	S.W. by S.	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$
Sandy hummock	N. 19	E.	——	N. 15	E.	——		6   0	4  57
Furthest extreme	S. 53	E.	——	S. 61	E.	——
The sandy hummock	N. 12	W.	East.	N. 18	W.	S.W. by S.	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$	5  30	5  13
Projecting part of the coast	S. 59	E.	——	S. 64	E.
Mean increase								5  54	5  33

 

Another example occurred whilst working up to King's Island, in Bass' Strait, where the dip is 68°; on changing the ship's head from West to S.E. ½ S., the decrease of east variation from five bearings was 4° 48′; from the common multiplier it would be 5° 33′. The bearings therefore showed differences the same way, and nearly the same in quantity as did the azimuths and amplitudes: that they should do so exactly, is not to be expected; for if azimuths, and especially amplitudes taken at sea with the present compasses, cannot be depended upon nearer than to half a degree on either side, as I believe they cannot, even under the most favourable circumstances, the best bearings set by hand are likely to err a degree on either side, and two degrees where there is much