35& 
MAGNETIC SURVEY OF A PART OF THE SOUTHERN HEMISPHERE. 
Values of 
Ship’s head. 
Observed Intensity. 
Ship’s head. 
Observed Intensity. 
King George’s 
Sound. 
Mauritius. 
Cape of Good 
Hope. 
King George’s 
Sound. 
Mauritius. 
Cape of Good 
Hope. 
N. 
1-737 
1-150 
1-024 
S. 
1-799 
1-206 
1-066 
N.N.W. 
1-736 
1-152 
1-020 
S.S.E. 
1-797 
1-204 
1-055 
N.W. 
1-734 
1-151 
1-025 
S.E. 
1-790 
1-182 
1-045 
W.N.W. 
1-752 
1-158 
1-025 
E.S.E. 
1-773 
1-189 
1-032 
W. 
1-758 
1-166 
1-028 
E. 
1-753 
1-169 
1-029 
W.S.W. 
1'775 
1-198 
1-036 
E.N.E. 
1-757 
1-166 
1-024 
s.w. 
1-790 
1-191 
1-049 
N.E. 
1-736 
1-159 
1-023 
s.s.w. 
1-805 
1-200 
1-061 
N.N.E. 
1-735 
1-155 
1-023 
“ The observed values of 6 and <p- are approximately — 
King George’s Sound . . 0= — 65 11; <p=l'733 
Mauritius 0= — 54 14; <p=T158 
Cape of Good Hope . . . 0= — 53 37; <p=r027. 
“ Substituting these values in equations (1.) and (2.), we have 
King George’s Sound . . a= , 0242; b — '9905; 
Mauritius a = '0234; 6=1-0105 ; 
Cape of Good Hope . . . a=*0186; b— '9916. 
<c Including these values with those obtained from the compass observations, we 
get the mean values for a and b , 
«='0237; 6=*9912. 
“ The constants c and d are calculated from the formula 
ccos tan 6= b sin £ cosec tan & 
for the observations between N.N.W. and S.S.W., and N.N.E. and S.S.E. ; and for 
the other points, viz. N. and S., by the formula 
ccos £-J-fi?tan0=(cos£+atan0) sec tan & . 
“ The values of £ and &' were given by the observations at the several stations. The 
values of c and d are as follows : — 
King George’s Sound . . c='010 ; <f=l'054; 
Mauritius c='014 ; c?=r01l ; 
Cape of Good Hope . . ^ c='003 ; c?=T033. 
The values of c and d were also obtained from the observations of dip and intensity, 
independently of a and b, by the formula 
a' 
c cos & cos Z,—d sin 0= — sin &, 
A being supposed equal to unity; which gives the following values: — 
