MAJOR SABINE ON TERRESTRIAL MAGNETISM. 
151 
at stations where the values are approximately known by the concurrence of other ob- 
servers of recent date, are as follows, proceeding- from Plymouth as a base station : 
Cape of Good Hope . . . 1*030; and by other observers . . 1*016* 
Hobart Town 1*830 ; and by other observers . . 1*814/ 
Sydney P691 ; and by other observers . . 1*675^. 
Captain Wickham’s values, it may be seen, are in excess, which is a difference of a 
contrary nature to that which would have been occasioned by a loss of magnetism ; 
we may therefore conclude, with much probability, that needle Z sustained no notable 
loss of magnetism during the whole of its employment, except that which the obser- 
vations at Swan River show to have taken place between November 1837 and June 
1838 : the results with this needle, contained in the next Table, have been computed 
accordingly. 
In the case of needle Y, which appears to have lost magnetism between Plymouth 
and Santa Cruz, but to what amount the observations supply no certain means of 
deciding, we may take as base-stations, from the other extremity of the series, Sydney 
and Hobart Town, where we have already seen that the values of the intensity are 
approximately known, viz. 1*675 and 1*8 14. Allowing the loss of 7 S ‘6, evidenced by 
the observations at Swan River, the results computed with this needle at Santa Cruz, 
and all the subsequent stations, accord well with those of needle Z, and with those 
of other observers ; whence we may infer with much probability, that between July 
1837 at Santa Cruz, and April 1839 at Sydney, needle Y sustained no other loss of 
magnetism than that deducible from the observations themselves. The results with 
this needle contained in the next Table have been computed accordingly. 
The loss of magnetism between the observations at Swan River in November 1837 
and June 1838, has been regarded as a gradual and uniform loss during the whole 
interval, in the absence of any satisfactory evidence to the contrary. 
The results thus computed and inserted in the following Table must be considered 
as strictly provisional ; the absolute measurements of the intensity about to be exe- 
cuted at the Cape of Good Hope by Lieut. Eardley Wilmot, R.A., and at Sydney and 
Van Diemen’s Land by Captain James Ross, R.N., will supply important stations of 
reference in the ultimate revision of this series ; based on exact measures at these sta- 
tions, and corrected for the variations of temperature, Captain Wickham’s observations 
may be expected to give the relative values of the intensity at the intermediate sta- 
tions, with, what would now at least be considered, a high degree of precision. 
* _ , T , /FitzRoy .. .. 1836 1*0141 
* Cape of Good Hopes _ >1-011. 
LFranklin . . 1836 1*008 J 
tFitzRoy 1836 1-8171 
f Hobart Town \ f 1837 1 >1-814. 
r™ 1 " 1 1838 f 1 ' 810 / 
. 0 , TDunlop ....1831 1-6651 
tSyd " e5 ' \FitzRoy .... 1886 i W 1 ’ 675 ' 
