LIEUT. CLERK’S REPORT: ELEMENTS OF REDUCTION. 
361 
“ Magnets N and S are the small magnets belonging to the apparatus used con- 
jointly ; deflector N and deflector S are the respective poles of the spare needle, 
-j- 13' has been applied in all cases except when only magnets N and S have been 
used, in which case +24' has been used, that being the mean correction for direct 
and magnets N and S. 
“ For the index corrections for needle A of C. 9, we have only an observation in 
Simon’s Bay, Cape of Good Hope, before starting. Needle A was used from the 
Cape to King George’s Sound, and was observed on shore at King George’s Sound 
on the 7th of April. On the 10th it was found, from the discordance of the observa- 
tions, that its axle had been damaged since the observations on the 7th, it was there- 
fore taken out and needle B mounted in its place. The instrument had a third needle 
C which was used as a deflector. The small magnets were also used, both conjointly 
and separately. The observation in Simon’s Bay gives, — 
For C. 9, needle A 
Corrected inclination, needle 1 . . . 
-53° 24'') 
—53° 50' J 
Index correction —26'. 
This correction has been applied to all observations made with needle A of C. 9. For 
the correction of needle B, we have a comparison at the Cape of Good Hope after 
the return of the Expedition, and also at Woolwich, in January 1846. All observa- 
tions with this instrument were taken with the face east. 
“ The following are the observations at the Cape : — 
Date. 
Observed Inclination. — Face East. 
True 
Inclination. 
Index 
correc- 
tion. 
Direct. 
Def. N. 
Def. S. 
Mag. N and S. 
Mag. N. 
Mag. S. 
Mean. 
1845. 
June 30. 
July 2. 
° X 
-53 56 
— 53 41 
o / 
— 54 15 
— 54 11 
-52 47 
—52 55 
—54 06' 
-54 15 
-53 29 
-53 49 
—53 23 
-53 41 
-53 40 
-53 45 
-53 25 
-53 25 
+ 15 
+ 20 
Mean... 
— 53 48 
-54 13 
-52 51 
— 54 10 
-53 39 
-53 32 
-53 43 
-53 25 
+ 18 
“ And at Woolwich : — 
Date. 
Observed Inclination. — Face East. 
True 
Inclination. 
Index 
correc- 
tion. 
Direct. 
Def. N. 
Def. S. 
Mag. N and S. 
Mag. N. 
Mag. S. 
Mean. 
1846. 
Jan. 13. 
15. 
+ 68 58 
+ 68 56 
+ 68 02 
+ 68 21 
+ 68 37 
+ 68 52 
+ 68 24 
+ 68 45 
+ 68 32 
+ 68 35 
+ 68 30 
+ 68 34 
+ 68 31 
+ 68 41 
j +68 58 
/ 
+ 22 
Mean... 
+ 68 57 
+ 68 12 
+ 68 44 
+ 68 35 
+ 68 33 
+ 68 32 
+ 68 36 
+ 68 58 
+ 22 
“ The index correction obtained at the Cape has been used for all the observa- 
tions taken with this needle. 
