horizontal needle when under the influence of magnets. 357 
I have stated that the deviations are those actually observed 
from 180 0 or the south point, and the mean deviations will 
be from the same point ; but to have the mean deviations 
from the most stationary point, or that which should be 
considered as zero, it is necessary to ascertain, as correctly 
as possible, the mean time of the needle being stationary, and 
its mean direction at that time. Now we have the observa- 
tions at every hour from three till eleven on every day but 
the 20th and 27th, and taking the means of these six days, 
we shall have the deviations as under. 
at 3 h o m P. M. -j- o° 1 2' 
4 0 _ ” 4 " 0 45 
5 o - - 4* 0 59 
60 - - -f 1 11 
70 - _ + 1 25 
80 - - -j- 1 23 
9 ° - - 4 - 1 25 
10 o - - -j- 1 2 6 
no - - 4~ 1 27 
So that from seven o’clock the mean change in direction 
is extremely small, and the mean situation of the stationary 
point is + 1° 25'. Considering this point as zero, we shall 
have the mean deviations at the different hours as follow : 
Time. 
Deviation. 
h. m. 
0 / 
7 0 
+ 0 54 
7 3 ° 
+ I 1 2 
8 0 
+ I O5 
9 0 
+ O 44 
10 0 
O 02 
1 1 0 
I OI 
Noon. 
— I 31 
1 0 
— i 37 
2 0 
— i 37 
3 0 
— 1 *3 
4 0 
— 0 40 
5 0 
— 0 26 
6 0 
— 0 13 
7 0 
0 00 
