There can be no doubt that the philosophical activity here alluded to was the direct issue of the political and military event to which we have referred it. The tastes and genius of Alexander were manifested by his relations to Aristotle, whose studies in natural history he promoted by the collection of a menagerie; and in astronomy, by transmitting to him, through Callisthenes, the records of Babylonian observations extending over 1903 years. His biography, as we have seen, shows a personal interest in the cultivation of such studies. In this particular other great soldiers have resembled him; and perhaps it may be inferred that the practical habit of thought and accommodation of theory to the actual purposes of life pre-eminently required by their profession, leads them spontaneously to decline speculative uncertainties, and to be satisfied only with things that are real and exact. [Sidenote: The great men it produced.] Under the inspiration of the system of Alexander, and guided by the suggestions of certain great men who had caught the spirit of the times, the Egyptian kings thus created, under their own immediate auspices, the Museum. State policy, operating in the manner I have previously described, furnished them with an additional theological reason for founding this establishment. In the Macedonian campaign a vast amount of engineering and mathematical talent had been necessarily stimulated into existence, for great armies cannot be handled, great marches cannot be made, nor great battles fought without that result. When the period of energetic action was over, and to the military operations succeeded comparative repose and temporary moments of peace, the talent thus called forth found occupation in the way most congenial to it by cultivating mathematical and physical studies. In Alexandria, itself a monument of engineering and architectural skill, soon were to be found men whose names were destined for futurity--Apollonius, Eratosthenes, Manetho. Of these, one may be selected for the remark that, while speculative philosophers were occupying themselves with discussions respecting the criterion of truth, and, upon the whole, coming to the conclusion that no such thing existed, and that, if the truth was actually in the possession of man, he had no means of knowing it, Euclid of Alexandria was writing an immortal work, destined to challenge contradiction from the whole human race, and to make good its title as the representative of absolute and undeniable truth--truth not to be gainsaid in any nation or at any time. We still use the geometry of Euclid in our schools. [Sidenote: The writings of Euclid.]