74 
On the Variations in Personal Equation 
measure of the relative uncertainty of the observer in making his estimate in the 
two difterent Experiments. 
There is some evidence for a slight periodicity in the judgments in the 
Bisection Series ; if there is any period in the Trisections it must cover at least 
26 observations, for there is no indication of a significant increase in the values of 
as far as calculated, i.e. up to Rja. 
VIII. Experiment C. Counting of 10 Seconds. Reduction of 
Observations. 
{a) The Individual Series. 
The values of dj , and for eaeli of the 20 series are given in Table XII as 
well as the hour and date ; the means (f/,) have been plotted to the order of series 
in Figure 13. 
If x is the mean in the factor e/p for a series, 
y the order of series, 
2 the time in hours and fractions of an hour between 2.0 p.m. on December 
13, and the commencement of series 
we have for the regression lines, 
X - -9186 = - -006056 (y - 10-5) (xxxvi), 
X - -9186 = - -001552 {z - 38-24) (xxxvii), 
1- 
Personal Equation — Order of Series 
0- / "* 
i: Mean at -9186 
9 - 
; ',— Regression -9 1 86 =- -006050 (i/- 1 0-5) 
7- 
5- 1 
3^ ' ■ 
j E Mean \ 
i / ' \ ^\ \ 
B-1 -O 
* ^\ 
o „ 
5 - ~ 
1 { 1 1 1 1 
Ill 1 1 * 1 
X VII XIX 
XVI XVIII XX 
II IV VI VIII X XII .\ 
Fig. 18. 10 Second Counting, y, Order or Number of Series 
of which the first is represented in Figure 13. 
The coefiicients of correlation are, 
Txy = - -754 ± -065, ?•« = - -775 + -060, 
■ ■ 
: + -977 + -007, 
