The title-page of this book necessarily bears the name of one man but the reader will find in its pages the story, or part of the story, of many other Pioneers Of Progress. The crowning achievement Of anticipating the hypothesis Of Copernicus belongs to Aristarchus Of Samos alone; but to see it in its proper setting it is necessary to have followed in the footsteps of the earlier pioneers who, by one bold speculation after another, brought the solution of the problem nearer, though no one before Aristarchus actually hit upon the truth. This is why the writer has thought it useful to prefix to his account Of Aristarchus a short sketch Of the history of the development of astronomy in Greece down to Aristarchus's time, which is indeed the most fascinating portion of the story of Greek astronomy.