SURVEY OF THE BRITISH ISLES FOR THE EPOCH JAI^UARY 1, 1891. 27 
All the values of ^ obtained from the above Tables are collected below. 
Date. 
Dip circle. 
No. 74. 
No. 83. 
No. 94. 
No. 99. 
Sept.-Oct., 1887 . 
3-6-6 
/ 
Oct., 1887 .... 
-fO-S 
.liine 2-6, 1890 . . . 
+ 0-4 
„ 14-19, 1890 . . 
+ 1-6 
April 20-22, 1891 . . 
+ 1-4 
Oct. 13-16, 1891 . . 
+ 0-2 
+ 0-4 
Feb. 12, 1892 . . . 
.. 
-0'4 
Marcli 25, 1892 . . 
0-8 
Oct. 7-10, 1892 . . 
-0-5 
„ 11-13, „ . . 
, , 
, , 
-f 0-5 
„ 20-21, „ . . 
, , 
+ 0-7 
„ 24-25, „ . . 
-0-6 
None of these numbers, except perhaps those obtained from the observations made 
with No. 83 in 1890-91, are large enough to make it necessary to apply a correction 
to Dips measured with the Instruments. As regards No. 83, it was not used in 1891, 
and the correction which would be applied for 1890, though relatively large, is 
absolutely small. We therefore decided that the readings of the Dip Circles should 
be used without correction. 
The mean of the yd’s is + O'A, so that on the average the Survey Instruments read 
O'A below the Kew Standard. 
Summary of Differences hetiveen Kew and Survey Standards. 
The final conclusion therefore to which we come, as the result of our comparisons 
with the Kew Standards, is that to reduce either our observations at any particular 
place, or the calculated values, deduced from our iso-magnetics, to what they would 
have been if the Kew Instruments had been used— 
(1) The Declinations must be increased by 2''5, and 
(2) The Horizontal Forces diminished by 0'0023 metric or 0'00023 C.G.S. unit. 
(3) The Dips require no correction. 
It will, of course, be understood that the results to which these corrections are 
applied, have been already reduced to the Survey Standard by means of the Tables 
given above. 
Time Signals. 
We have again to thank Admiral Wharton, R.N., F.K.S., Chief Hydrographer to 
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