I'.E PROBABILITY
independent of the number of Variates, so long as they are sufficiently numerous to secure statistical constancy.
Show numerous schemes of variates of different kinds, and remark on the prevalent family likeness between the bounding curves. (Words and meanings learnt-Schemes of Distribution, Centesimal graduation of base.)
The third lesson passes from Variates, measured upwards from the base, to Deviates measured upwards or downwards from the Median, and treated as positive or negative values accordingly (Fig. 6).
Draw a Scheme of Variates on the blackboard, and show that it consists of two parts ; the median which represents a constant, and the curve which represents the variations from it. Draw a horizontal line from limit to limit, through the top of the Median to serve as Axis to the Curve. Divide the Axis centesimally, and wipe out everything except Curve, Axis, and Limits. This forms a Scheme of Distribution of Deviates. Draw ordinates from the axis to the curve at the 25th and 75th divisions. These are the
Quartile' deviates.
At this stage the Genesis of the theoretical Normal curve might be briefly explained and the generality of its application ; also some of its beautiful properties of reproduction. Many of the diagrams already shown would be again employed to show the prevalence of approximately normal distributions. Excep-
