78 
MR. A. W. RtiCKER AND DR. T. E. THORPE ON A MAGNETIC 
Declination Observations. 
Observer. 
Instrument. 
Mean values of 
f-fo- 
W. 
dS. 
Scotland .... 
R. and T. 
60 and 61 
+ 0-31 
+ 0-39 
+ 0-75 
+ 077 
England .... 
T. 
61 
+ 0-39 
+ 0-32 
+ 0-28 
+ 071 
R. 
60 
+ 0-45 
+ 0-35 
+ 0-39 
+ 0-85 
Ireland. 
T. 
61 
+ 0-48 
+ 0-24 
+ 0-37 
+ 0-51 
R. 
60 
+ 0-39 
+ 0-32 
+ 0-42 
+ 0-63 
Iloughly then, the average errors due to imperfect adjustment of the mirror, 
to inaccuracy in determining the magnetic axis of the magnet, and to torsion, ought 
not, in each case, to exceed about 0'4 of a minute of arc, assuming that no correction 
was attempted, as would be the case, for instance, with regard to /r, if no back 
observations of the sun were taken. As in the great majority of cases, all three were 
corrected by front and back observations on the sun, by observing the magnet erect 
and inverted, and by determining the torsion, we may be sure that the actual errors 
were much below these amounts. It seems, therefore, probable that the observations 
are affected with small errors which are not so capable of correction, for the mean and 
probable values of c^S appear to prove that it is an even chance that each of two 
independent declinations differ from their mean by more than 0''7. 
In the following Table we give a similar analysis of the Force observations. The 
quantity e/2 is the percentage difference of either deflection experiment from their 
mean. 
dT is the average difference in seconds between each “independent” determination 
of the time of a single oscillation (as defined on p. 73) and their mean. 
f/H is the average difference between each independent determination of the Hori¬ 
zontal Forces and the mean of the two involved in each complete experiment. In all 
cases the averages are, of course, taken without reference to sign. 
Horizontal Force. 
Observer. 
Instrument. 
Mean values of 
e/2. 
dT. 
dH. 
Scotland . 
R. and T. 
60 and 61 
Per cent. 
+ 0-041 
S. 
+ 0*00043 
M.U. 
+ 0-00033 
England . . 
T. 
61 
0-031 
0-00040 
0-00030 
R. 
60 
0-023 
0-00035 
0-00025 
Ireland . 
T. 
61 
0-033 
0-00032 
0-00028 
R. 
60 
0-017 
0-00040 
0-00022 
