LIEUT. CLERK’S REPORT: ELEMENTS OF REDUCTION. 359 
King George’s Sound . . c= - 028 ; d= 1*023; 
Mauritius c=‘024 ; d=l'0l7 ; 
Cape of Good Hope . . . c=-021 ; d=l'020. 
“ The mean of these six values makes 
c— 017; d— 1-026. 
“ From these values of a, b, c and d , a table of corrections was found by means of 
equations (12.) and (13.) (Contribution V.), employing calculated values of 
“ In order to test the accuracy of the table, we may compare observed and calcu- 
lated values of the dip at King George’s Sound. It will be seen that on the northerly 
points the correction is rather too large, on the easterly and westerly too small, and 
nearly correct on the S., S.S.W, and S.S.E. points. The differences however are 
within the limits of observation errors. 
Ship’s head. 
Observed Incli- 
nation. 
Tabular correc- 
tion. 
Corrected Inclination. ; 
N. 
n.n.w. and n.n.e. 
n.w. and n.e. 
w.n.w. and e.n.e. 
w. and e. 
w.s.w. and e.s.e. 
s.w. and s.e. 
s.s.w. and s.s.e. 
s. 
— 66 15 
—66 32 
-66 18 
-66 07 
-66 03 
— 65 47 
—65 30 
— 64 54 
—64 52 
+ 1 23 
+ 1 23 
+ 1 31 
+ 1 09 
+ 0 46 
+ 0 23 
+ 0 02 
-0 16 
— 0 18 
o / O / 
-64 52q 
-65 09 
-64 47 
-64 58 
—65 17 >—65 08 
-65 24 
—65 28 
—65 10 
-65 10 J 
The mean inclination observed on shore with the same needle being —65° 11'. 
“3. Calculation of Corrections for Intensity Observations. 
“The constant A is calculated from the above observations by means of the formula 
sin d —c cos 0 cos sin 0. 
“The values of 0', <p' and are all given by the observations on the sixteen points 
of the compass; those of <p and 6 by the observations on shore. The following are 
the resulting values for A', viz. — 
King George’s Sound . . . A'=0’998 
Mauritius A'=0'992 
Cape of Good Hope .... A'=0‘992 
Mean . . A'=0 - 994 
“ This value being so near unity, A is assumed =T0, with which and the values of 
c and d already determined, a table of corrections was formed by means of the equation 
~ =A'c0~ tan 0-\- cos 2^ cos 0 cosec 0'*, 
d and £ being obtained from the tables for correcting the dips and declinations. 
* Philosophical Transactions, 1843, Part II. p. 162. 
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