Some philosophical remarks from the introduction, "Scientific Research", to Edwin Hubble's "The Realm of the Nebulae" (1936).

Hubble is discussing the nature of scientific knowledge to be, unlike other fields of human knowledge, cumulative; that is, it builds on earlier achievements and discoveries.

This remarkable attibute of science is bought at a price--the strict limitation of the subject matter. "Science," as Campbell* remarks, "deals with judgements concerning which it is possible to obtain universal agreement." These data are not individual events, but the invariable associations of events or properties which are known as laws of science. Agreement is secured by observation and experiment. The tests represent external authorities which all men must acknowledge, by their actions if not by their words, in order to survive.

Science, since it deals only with such judgements, is necessarily barred from the world of values. There no external authority is known. Each man appeals to his private god and recognizes no superior court of appeal. Wisdom is a personal achievement and is difficult to transmit.

...

The special methods of science are efficient and powerful when they are used within their proper field--the region closed and bounded by the necessity for agreement on the subject matter. The methods are so successful, indeed, that attempts are constantly made to apply them in other fields--to the study of things as they should be rather than things as they are. The results are seldom convincing. The calculus of values, if it is ever formulated, will probably have little in common with the calculus of science.