SURVEY OF THE BRITISH ISLES FOR THE EPOCH JANUARY I, 1891. 
21 
Comparison of Maofnetometer 73 with the Kew Standard. 
o 
Date. 
Observer. 
S 
(Survey 
Instrument). 
K 
(Kew 
In.strument). 
K-S=/3. 
1 
11 
S-K' 
= 0-000. 
Marcl) 2J, 1 892 
G. 
1-8] 60 
1-8166 
+ 0-0006 
1-8160 
0 
„ 23, „ ... 
G. 
1-8150 
1-8159 
+ 0-0009 
1-8153 
- 3 
„ 2.3, „ ... 
G. 
1-8152 
1-8161 
+ 0-0009 
1-8155 
— .3 
G. 
1-8163 
1-8173 
+ 0-0010 
1-8167 
- 4 
„ 24, • „ ... 
G. 
1-8163 
1-8170 
+ 0-0007 
1-8164 
- 1 
„ 24, „ ... 
G. 
1-8172 
1-8178 
+ 0-0006 
1-8172 
0 
„ 24, „ ... 
G. 
1-8180 
1-8179 
-0-0001 
1-8173 
+ 7 
,, 25, ,, ... 
G. 
1-8130 
1-8129 
- 0-0001 
1-8123 
+ 7 
„ 25, „ ... 
G. 
1*8137 
1-8143 
+ 0-0006 
1-8137 
0 
/i=+0-0006 
Mean = 
± 2-S 
Oct. 11, 1892 .... 
W. 
1*8137 
1-8146 
+ 0-0009 
1-81.39 
- 2 
„ 11, „ .... 
W. 
1-8135 
1 -8143 
+ 0-0008 
- 1-81.36 
- 1 
„ 11, „ ... . 
W. 
1-8162 
1-8188 
+ 0-0026 
1-8181 
-19 
,, 13, ,, .... 
W. 
1-8167 
1-8162 
-0-0005 
1*8155 
+ 12 
„ 1.3, „ .... 
W. 
] -8163 
1-8164 
+ 0*0001 
1-8157 
+ 6 
„ 1.3, „ .... 
W. 
1-8167 
1-8173 
+ 0-0006 
1*8166 
+ 1 
y3=+0-0007 
Mean = 
± 6-8 
Magnetometers 60 and 61 were in such close accord in 1887 that we may regard 
the mean value of viz., — 0'0023, as common to both of them at that date, i.e., 
we assume that both instruments then gave results 0'0023 metric or 0'00023 
C.G.S. unit above the Kew Standard. This is therefore the Survey Standard. To 
tind the correction to be applied to any instrument to reduce it to the Survey 
Standard, we must add 0'0023 to the value of yd. The numbers so obtained are 
shown in the following Table, in which the corrections are expressed in terms of 
O'OOOl metric unit :— 
