value as the other or at least deviates so little from it that the difference in proportion to its own quantity and for our purposes is of no account?
Evidently not. That would be asking too much, and is not necessarily obtained even by the natural sciences. Then, perhaps it is when the averages from larger groups of experiments exhibit the characteristics mentioned above?
Again evidently not. That would be asking too little. For, if observation of processes that resemble each other from any point of view are thrown together in sufficiently large numbers, fairly constant mean values are almost everywhere obtained which, nevertheless, possess little or no importance for the purposes which we have here. The exact distance of two signal poles, the position of a star at a certain hour, the expansion of a metal for a certain increase of temperature, all the numerous coefficients and other constants of physics and chemistry are given us as average values which only approximate to a high degree of constancy. On the other hand the number of suicides in a certain month, the average length of life in a given place, the number of teams and pedestrians per day at a certain street corner, and the like, are also noticeably constant, each being an average from large groups of observations. But both kinds of numbers, which I shall temporarily denote as constants of natural science and statistical constants, are, as everybody knows, constant from different causes and with entirely different significance for the knowledge of causal relations.
These differences can be formulated as follows:—
In the case of the constants of the natural sciences each individual effect is produced by a combination of causes exactly alike. The individual values come out somewhat differently because a certain number of those causes do not always join the combination with exactly the same values (e.g., there are little errors in the adjustment and reading of the instruments, irregularities in the texture or composition of the material examined or employed, etc.). However, experience teaches us that this fluctuation of separate causes does not occur absolutely irregularly but that as a rule it runs through or, rather, tries out limited and comparatively small circles of values symmetrically distributed around a central value. If several cases are brought together the effects of the separate deviations must more
