CHANCE, AND ITS ELIMINATION. 67 



effect nevertheless oscillates, and which is the middle 

 point in its oscillation ; we may conclude this to be 

 the effect of some constant cause : which cause, by 

 some of the methods already treated of, we may hope 

 to detect. This may be called the discovery of a resi- 

 dual phenomenon by eliminating the effect of chance. 



It is in this manner, for example, that loaded dice 

 may be discovered. Of course no dice are so clum- 

 sily loaded that they must always throw certain 

 numbers ; otherwise the fraud would be instantly 

 detected. The loading, a constant cause, mingles 

 with the changeable causes which determine what 

 cast will be thrown in each individual instance. If 

 the dice were not loaded, and the throw were left to 

 depend entirely upon the changeable causes, these in 

 a sufficient number of instances would balance one 

 another, and there would be no preponderant number 

 of throws of any one kind. If, therefore, after such a 

 number of trials that no further increase of their 

 number has any material effect upon the average, we 

 find a preponderance in favour of a particular throw ; 

 we may conclude with assurance that there is some 

 constant cause acting in favour of that throw, or in 

 other words, that the dice are not fair ; and moreover 

 the exact amount of the unfairness. In a similar 

 manner, what is called the diurnal variation of the 

 barometer, which is very small compared with the 

 variations arising from the irregular changes in the 

 state of the atmosphere, was discovered by comparing 

 the average height of the barometer at different hours 

 of the day. When this comparison was made, it was 

 found that there was a small difference, which on the 

 average was constant, however the absolute quantities 

 might vary, and which difference, therefore, must be 

 the effect of a constant cause. This cause was after- 



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