Page:Mind (Old Series) Volume 11.djvu/235

 234 J. M. CATTELL : making up the series, and a lf a 2, a 3 ,. . a n are the values of the several reactions, then (A-a 1 ) + (A-q 2 ) + (A-a 3 )+. . . +(A-q n ) n all the differences being taken as positive. The averages under R in the Tables (except when expressly stated) are taken from the 26 observations which made up the series, the averages under R' from the 20 reactions of the corrected series. Table I. gives the results of twenty series, made at intervals during a period of six months. TABLE I. 1885. ] B C j R V R' V R V R' V 12. I 140 10 141 8 144 12 1-43 8 16 145 137 10 16 143 139 6 11 136 133 9 16 138 128 5 11 30 156 131 10 13 155 131 7 9 147 149 15 9 150 151 11 6 27. II 152 148 13 14 149 147 9 8 143 146 11 10 143 144 9 7 28 160 139 13 13 162 142 8 11 144 149 9 9 144 149 6 6 31. Ill 161 152 164 15 13 14 163 149 164 9 7 8 146 144 163 9 9 9 146 143 163 5 6 6 3. IV 151 133 10 16 153 132 6 11 150 143 8 8 151 144 5 5 4 157 165 9 13 159 170 6 9 138 161 11 9 136 163 7 5 5 144 13 147 9 147 9 148 6 7 168 9 170 5 148 17 148 9 2. VII 137 16 140 11 158 12 158 6 4 152 13 155 9 140 14 145 9 A. 150 13 151 8 146 11 147 7 The Table shows that the average of 520 reactions on daylight reflected from a white surface was, for B 150, for C 146<r ; or, if the series are corrected by the method explained, the averages for both B and C become Iff longer. The average of the mean- variation of the reactions from the series to which they belong was for B 13, for C ll<r ; in the corrected series it becomes respectively 8 and la. It will be seen from the Table that the series made at different times do not differ greatly from each other ; the mean-variation of the twenty series is B 9, C 5. The reaction-time for practised observers is consequently quite a constant quantity ; when a reaction is made it will only differ