munity which is making for degeneracy. The study of eugenics centers round the actuarial treatment of human society in all its phases, healthy and morbid.
In every branch of science there exist, I believe, three chief stages of development. These stages are not always completely differentiated, and forms of the earlier stages may usefully survive into the later periods.
The first stage is the ideological. Men have formed ideas about phenomena on the basis of very limited experience. They spend their time and energy in discussing these ideas without much reference to the phenomena themselves. This discussion of ideas—this wrangling over definitions—is not idle. It not only led in medieval times to a philosophy which gave a by no means contemptible educational training; but in some of the most developed forms of science, as in the foundations of our most advanced pure mathematics, ideology can again do work of the greatest service. It corresponds to the pre-Baconian state of most sciences.
The second stage is the observational. It is a reaction against the purely introspective attempt at a natural philosophy. It consists in observing phenomena critically, and recording and describing their sequences. It is a fundamental stage towards any really scientific theory of nature. It will always remain a large factor in scientific work. But while it needs the mind of special width and creative power to invent a reasonable theory, and demonstrate it by the right type of observation, it is possible for the average man to observe carefully and to go on observing through a long lifetime. The result is the accumulation for decades and decades of observations made with little idea of testing a definite theory of organic or inorganic nature. These observations form a large proportion of scientific literature; and, I fear, are not always of service when the creative, scientist desires to test his theories. The time spent in hunting up data, which may after all fail to give the special small detail requisite, would often have sufficed to produce more adequate observations made ad hoc. Hence I think there will be, if there be not already, a reaction against purely observational or descriptive science.
The third stage in all science is the metrical. We proceed from observation to measurement, to accurate numerical expression of the sequences involved. It has been more than once asserted that by quantitative analysis you can not obtain more than lies in the data from which you start. The statement is either merely platitude; or else, if more than idle, it is false. The object of analysis is not to obtain more from data than exists therein; but to find out what actually does exist therein; and that is usually far from obvious to untrained inspection. The actual positions of the moon can be observed and recorded day by day. Such are the data. Shall we assert that lunar theory as it
