3 2 4 POPULAR SCIENCE MONTHLY 



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 under- 

 standing in the form in which we find it." 1 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. 2 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 orient- 

 ing 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 Brahe) ; (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 



1 ' The Evolution of the Scientific Investigator ' ( opening address of the 

 president of the International Congress of Arts and Science, at the St. Louis 

 Exposition), Science, Vol. XX., p. 385. 



2 The treatises by Berry ('A Short History of Astronomy,' London, 1898), 

 and Miss Agnes Clerke (in Appleton's ' Concise Knowledge Library,' New York, 

 1898), contain but a bare mention of the prior establishment of the Tychonian 

 and Copernican systems amongst the Greeks. Even the elaborate work of 

 Sir George Cornewall Lewis ('An Historical Survey of the Astronomy of the 

 Ancients,' London, 1862) can hardly be said to do justice to the evolution of 

 these systems. The French reading public is more fortunate than ours, having 

 a goodly number of popular works at its disposal. Two only need be men- 

 tioned here, each of them being provided with ample bibliographical references. 

 These are: Thirion, J., ' L'evolution de l'astronomie chez les Grecs ' (Brussels, 

 1900) ; and Bonnel, J. F., 'Etude sur l'histoire de l'astronomie: la Decouverte 

 du double Mouvement de la Terre ' (Tours, 1886). 



