a 
ON COMPARISON OF MAGNETIC INSTRUMENTS. 91 
with No. 70 were interpolated between those made with the Kew instru- 
ment, that with No. 70 on October 9 has been combined with the second 
result obtained on October 10 with the Kew instrument. 
These observations indicate that a small change took place in mag- 
netometer No. 70 during the journeys to the other observatories. The 
differences are not very great, and if we take the mean of the results 
obtained in July and October, viz. — 0':4, for the difference in declination, 
and —0-00011 for that in horizontal force, the final results will only be 
affected with an uncertainty of +0'-3 and +0-00007 respectively. 
In the case of the dip observations, experiments were either made 
with each instrument alternately, or so that the mean time of two 
observations made with one instrument was nearly the same as the mean 
time of two corresponding observations made with the other. In this 
way the effects of diurnal variation, &c., were nearly eliminated. We also, 
however, determined the dip at the time of each observation from the 
self-registering records of the horizontal and vertical force. 
Comparison of Dip Circle, Dover, No. 94 with the Kew Standard. 
Observers: Professor RickER and Mr. Watson. 
k=c=7, 
Instru- SSS SSS S'-—C=Z 
' Date Time |ment and) Dip Curve (C) | Needle 
Needle 
1 2 3 4 
H. M. ° ' ° , 
July 14 12 6 S 3 | 67 266 | 67 25:9 = +0°7 — 
r+ 12 42 Kl 23°8 255 | —1"°7 — —- _ 
a 13 16 S84 23°7 24-7 — =— — —1"0 
‘a 14 46 K 2 23°2 24°9 == —l'7 — 
a 15 16 $3 22°8 24:3 — —1'5 23 
i 1545| K1 24-9 ED ame = 
% 16 21 84 23:7 24-7 = — —1'0 
a 16 48 K2 | 2171 24:3 — = BID —— ARs 
July 25 11 38 K1 24:9 25°2 || —O"3 — — 
A 12 14 S83 22°6 24-6 = = —2'0 — 
a 12 34 S4 23:7 24-7 = — ai. —1"0 
A 12 55 K 2 23'8 24-7 — —0"9 = -—- 
Mean = —0'5 | —1"9 | —0"9 | —1"0 
4 ——__ —— —_F —— | 
(K—-S=-—0"3) — —1''2 —0''9 
H. M. f e) U 
October9 | 15 29 $3 67 24:4 | 67 25:2 — — —0'8 ae 
: _ 15 55 Ke 20:8 24-7 | —2'"4 — = — 
Octoberll | 10 39 K, 2 iy 23°2 25°4 —- —2'-2 — —_— 
“4 ll 24 8S 4 24:0 25:3 — — — —1'3 
+ 1l 51 Scan 23:7 25:0 — — —1'3 —_— 
* 12-22 K 1 209 24-7 | —3'8 — — _— 
ee 14 2 KL 22:3 23°8 | —1%5 — — — 
ar 14 33 8 4 22:0 24:0 == — —2"0 
9 14 51 Seo 21:7 23°5 — _— —L "8 _ 
“i 15 20 Ko 2 21°5 23-7 — —2'2 — 
Mean — —2'6 | —2'2 | —1'3 | —1°6 
——_-—— —\—_—_-_———" 
(K-S= -0'9) ee aBtea 15 
