the Royal Society’s Injiruments . 
393 
The inftrument being removed back to the Society’s 
houfe. 
Time. 
Variation by 
Diff. 
Time. 
Variation by 
Diff. 
r 
Society’s 
Inftrum. 
Compafs 
in room. 
Society’s 
Infirum. 
> 
Compafs 
in room. 
1 7 7 5 
h 
/ 
0 / • 
0 r 
/ 
1 7 7 5 
h 
O / 
0 / 
/ 
Aug. 2 
1 
8 V 
21 45 
21 32 
+ J 3 
Aug. 4 
IO 
5 oM 
21 47 
21 33 
+ H 
I 
10 
44 
3 ° 
+ 14 
I I 
0 
47 
34 
+ 13 
I 
20 
46 
29 
+ *7 
I I 
10 
47 
35 
+ 12 
I 
3 ° 
47 
29 
+ 18 
I I 
20 
47 
35 
+ 12 
I 
40 
47 
32 
+ J 5 
1 I 
3 ° 
46 
35 
+ 11 
I 
50 
47 
3 1 
+ 16 
I I 
40 
47 
34 
+ J 3 
2 
0 
47 
3 1 
+ 16 
By a mean of the obfervations, the variation fhewn by 
the compafs in the room is i',3 greater than by the So- 
ciety’s inftrument in the garden, and i4',i lefs than by 
the fame inftrument placed in its proper fituation; fo 
that the variation appears to be i 5^4 greater in that part 
of the Society’s Houfe where the compafs is placed, than 
in the abovementioned garden ; and therefore, as there 
is no likelihood of its being affected by any iron in the 
latter place, the needle feems to be drawn afide 15^- 
towards the N.W. by the iron work of the houfe and 
adjacent buildings. 
On comparing the obfervations of the two laft years 
together, the variation appears, after allowing for the 
error of the inftrument, to have been 27' greater in 1775 
than in 1774; though I have been informed by Dr. 
HEBERDEN, 
