An Introduction to a Biology 



of the first throw, tells us in what row the dot must be. 

 The figure 3, denoting the result of the second throw, tells 

 us in what column the dot must be. The square, therefore, 

 formed by the intersection of this row by this column is 

 that in which the dot must be placed. The next pair of throws 

 is a 6 followed by a 7. We find the position of the square 

 in which the dot representing this result is to be placed in 

 the same way. We continue this process mitil all the pairs 

 on the list are entered ; then we add up the dots, and write 

 the totals thus obtained, in each square ; add up the figures , 

 in each square composing a column, and write the total at 

 its base ; and add up the figures in each square composing 

 a row, and write the total at its end. The result is the 

 Correlation Table on p. 227. 



There is one feature of it which cannot fail to attract your 

 attention immediately. It is that the figure-containing 

 squares lie diagonally across the Table. It is not very dif- 

 ficult to see what this means. It is the expression of a fact 

 we already know, namely, that low numbers are associated 

 in a pair mth low numbers, high ones with high ones, and 

 intermediate ones with intermediate ones. 



We are now approaching the outskirts of a vast sub- 

 ject. The task I set myself was to show you the way to it ; 

 but not the way into it. Having given you an account of 

 Weldon's device for illustrating correlation, I will go no 

 further, but will leave you in the hands of the statistician, 

 who, I may perhaps tell you, will provide you with a means 

 of working out from such a Table a number called the cor- 

 relation coefficient, which is a measure of the degree of con- 

 nection between the two things you are dealing with. In 

 the case of the dice throws connected in the way we have 

 just been considering, this number will be approximately 

 •5. In the case of Table (p. 232) it will be approximately 

 0; in the case of Table XII. (p. 238), approximately 1. 

 In fact, quite generally, if m dice are left down in the 12 the 

 coefficient is m/r2ths. 



22fJ 



