106 
LIEUT.-COLONEL SABINE ON TERRESTRIAL MAGNETISM. 
plete process for determining the true inclination was gone through with other 
needles, were as follows : — 
Hobarton. 
Sydney. 
New Zealand. 
Falkland Islands. 
Observed . . <j 
' Face East - 
Face West - 
-7°0 17-3 
-70 44-8 
— 62 22-4 
— 62 56-5 
— 58 50-6 
— 60 02'8 
— 51 38*4 
— 52 57‘2 
Mean 
• . . . — 
-70 31T 
— 62 39-5 
-59 267 
— 52 17*8 
True inclination 
-70 40-7 
— 62 49T 
-59 31-9 
— 52 26-3 
"Face East 
— 23-4 
— 267 
— 41-3 
-47'9 
Index correction^ 
Face West 
-f* 4T 
+ 7’4 
+ 30-9 
+30-9 
JMean . . 
• - 9-7 
— 9-6 
— 5*2 
— 8-5 
Differences face East and West 
27*5 
34-1 
722 
78-8 
The corrections of the mean results with F. C. B. at the four stations accord well 
within the limits of observation error. On examining the differences in the results 
with the face east and face west, and the corrections severally required in the two 
positions at the four stations, it appears probable that a very slight derangement of 
some part of the instrument took place between the observations at Sydney and those 
at the Bay of Islands, which caused the partial results with the face east and face 
west to diverge more from each other than they had done previously, but without 
affecting the mean results. A note which accompanied the observations to England 
shows that Captain Crozier considered that some slight change had taken place in 
the amount of the index correction with the face east, but was unable to assign its 
date or its cause. In the absence of any distinct evidence in these respects, — and in 
consideration of the insufficiency of the means of assigning the precise amount of the 
change, — I have preferred the employment of an arithmetical mean of the index cor- 
rections observed at the four stations ( — 35') during the whole course of the voyage. 
The uncertainty arising from this source cannot amount to more than a very few 
minutes in any portion of the voyage. 
For the index correction with deflector N we have, 
Hobarton. 
Sydney. 
New Zealand. 
Falkland Islands. 
Face East . . . 
-69 33-5 
— 61 367 
— 57 58-0 
— 50 54-4 
Face West . . . 
— 71 259 
-63 007 
-60 12-3 
— 53 313 
Mean 
— 70 297 
-62 187 
-59 05*1 
-52 12-8 
True inclination 
-70 407 
— 62 49 1 
— 59 31-9 
— 52 26-3 
Index correction, face East 
. . —67 2 
-72-4 
— 93-9 
— 9T9 
Mean index correction, face East 
—81 
i 
