Page:Popular Science Monthly Volume 68.djvu/328

324 are interested. Indeed, precisely this sort of interest is recognized by Professor Simon Newcomb as one of the characteristics of modern science. The opening words of his presidential address at the St. Louis Congress tell us that "among the tendencies characteristic of the science of our day is one toward laying greater stress on questions of the beginnings of things, and regarding a knowledge of the laws of development of any object of study as necessary to its complete understanding in the form in which we find it." But interest alone is scarcely sufficient to overcome the difficulties which beset the general reader in quest of information, owing to the exceedingly scattered, and more or less special nature of the literature. The absence, too, of a popular conspectus which treats in satisfactory manner of the origin of the heliocentric hypothesis, is to be regretted. Hence the present article has been prepared with the idea of affording those who may be inquisitive as to the sources of information with the means of orienting themselves.

In order to keep the relations of the founders of different cosmical systems firmly in mind, the distinguishing features of the latter may be pointed out, with indication of the most prominent names associated with each. Four distinct systems may be recognized, according as the center of the universe is supposed be occupied by (1) a central fire, other than our sun (Philolaus the Pythagorean); (2) by a stationary earth about which the heavens revolve (Eudoxus of Cnidos, Ptolemy, Tycho Brahé); (3) by an earth rotating upon its axis, but otherwise immovable (Heraclides of Pontus); and (4) by the sun, about which the entire planetary system revolves (Aristarchus, Copernicus). As thus outlined, the transition between the third and fourth of these systems appears at first sight abrupt, but examination of the views of Heraclides shows that he too recognized the competency of the modern system as a working hypothesis, and thus helped prepare the way for its rigorous adoption. It is evident, also, that a somewhat remote