102 
On the Variatiojis in Personal Equntiem 
deviation vary both within a session and over long periods of time, and if there is 
any correlation between successive judgments, what is the form of the function i/r, 
which gives the value of the successive correlation coefficients in the relation 
It is only by a detailed analysis of the observations themselves or of others 
carried out ad hoc, copying them as closely as possible, that full information on 
these points can be obtained ; but if the possible complexities which may be present 
in the variations of judgment are fully realised, a great deal may be done in prac- 
tical cases by the arrangement of the observations and the combination of the 
results, to eliminate the factors whose magnitude is unknown and to correct for 
others which are more easy to ascertain. 
I have heartily to thank Miss I. McLearn for making the diagrams for Figs. 3, 
4, 8, 12, 17, 19 and 20, and Miss M. Noel Karn for assistance in some of the 
computation. 
V 
