less patent generalizations。 At the very outset； his grand division of the animal kingdom into blood…bearing and bloodless animals implies a very broad and philosophical conception of the entire animal kingdom。 The modern physiologist does not accept the classification； inasmuch as it is now known that colorless fluids perform the functions of blood for all the lower organisms。 But the fact remains that Aristotle's grand divisions correspond to the grand divisions of the Lamarckian systemvertebrates and invertebrates which every one now accepts。 Aristotle； as we have said； based his classification upon observation of the blood； Lamarck was guided by a study of the skeleton。 The fact that such diverse points of view could direct the observer towards the same result gives； inferentially； a suggestive lesson in what the modern physiologist calls the homologies of parts of the organism。 Aristotle divides his so…called blood…bearing animals into five classes： （1） Four…footed animals that bring forth their young alive； （2） birds； （3） egg…laying four… footed animals （including what modern naturalists call reptiles and amphibians）； （4） whales and their allies； （5） fishes。 This classification； as will be observed； is not so very far afield from the modern divisions into mammals； birds； reptiles； amphibians； and fishes。 That Aristotle should have recognized the fundamental distinction between fishes and the fish… like whales； dolphins； and porpoises proves the far from superficial character of his studies。 Aristotle knew that these animals breathe by means of lungs and that they produce living young。 He recognized； therefore； their affinity with his first class of animals； even if he did not； like the modern naturalist； consider these affinities close enough to justify bringing the two types together into a single class。 The bloodless animals were also divided by Aristotle into five classesnamely： （1） Cephalopoda （the octopus； cuttle…fish； etc。）； （2） weak…shelled animals （crabs； etc。）； （3） insects and their allies （including various forms； such as spiders and centipedes； which the modern classifier prefers to place by themselves）； （4） hard…shelled animals （clams； oysters； snails； etc。）； （5） a conglomerate group of marine forms； including star…fish； sea…urchins； and various anomalous forms that were regarded as linking the animal to the vegetable worlds。 This classification of the lower forms of animal life continued in vogue until Cuvier substituted for it his famous grouping into articulates； mollusks； and radiates； which grouping in turn was in part superseded later in the nineteenth century。 What Aristotle did for the animal kingdom his pupil； Theophrastus； did in some measure for the vegetable kingdom。 Theophrastus； however； was much less a classifier than his master； and his work on botany； called The Natural History of Development； pays comparatively slight attention to theoretical questions。 It deals largely with such practicalities as the making of charcoal； of pitch； and of resin； and the effects of various plants on the animal organism when taken as foods or as medicines。 In this regard the work of Theophrastus； is more nearly akin to the natural history of the famous Roman compiler； Pliny。 It remained； however； throughout antiquity as the most important work on its subject； and it entitles Theophrastus to be called the 〃father of botany。〃 Theophrastus deals also with the mineral kingdom after much the same fashion； and here again his work is the most notable that was produced in antiquity。
IX。 GREEK SCIENCE OF THE ALEXANDRIAN OR HELLENISTIC PERIOD We are entering now upon the most important scientific epoch of antiquity。 When Aristotle and Theophrastus passed from the scene； Athens ceased to be in any sense the scientific centre of the world。 That city still retained its reminiscent glory； and cannot be ignored in the history of culture； but no great scientific leader was ever again to be born or to take up his permanent abode within the confines of Greece proper。 With almost cataclysmic suddenness； a new intellectual centre appeared on the south shore of the Mediterranean。 This was the city of Alexandria； a city which Alexander the Great had founded during his brief visit to Egypt； and which became the capital of Ptolemy Soter when he chose Egypt as his portion of the dismembered empire of the great Macedonian。 Ptolemy had been with his master in the East； and was with him in Babylonia when he died。 He had therefore come personally in contact with Babylonian civilization； and we cannot doubt that this had a most important influence upon his life； and through him upon the new civilization of the West。 In point of culture； Alexandria must be regarded as the successor of Babylon； scarcely less directly than of Greece。 Following the Babylonian model； Ptolemy erected a great museum and began collecting a library。 Before his death it was said that he had collected no fewer than two hundred thousand manuscripts。 He had gathered also a company of great teachers and founded a school of science which； as has just been said； made Alexandria the culture…centre of the world。 Athens in the day of her prime had known nothing quite like this。 Such private citizens as Aristotle are known to have had libraries； but there were no great public collections of books in Athens； or in any other part of the Greek domain； until Ptolemy founded his famous library。 As is well known； such libraries had existed in Babylonia for thousands of years。 The character which the Ptolemaic epoch took on was no doubt due to Babylonian influence； but quite as much to the personal experience of Ptolemy himself as an explorer in the Far East。 The marvellous conquering journey of Alexander had enormously widened the horizon of the Greek geographer； and stimulated the imagination of all ranks of the people； It was but natural； then； that geography and its parent science astronomy should occupy the attention of the best minds in this succeeding epoch。 In point of fact； such a company of star…gazers and earth…measurers came upon the scene in this third century B。C。 as had never before existed anywhere in the world。 The whole trend of the time was towards mechanics。 It was as if the greatest thinkers had squarely faced about from the attitude of the mystical philosophers of the preceding century； and had set themselves the task of solving all the mechanical riddles of the universe； They no longer troubled themselves about problems of 〃being〃 and 〃becoming〃； they gave but little heed to metaphysical subtleties； they demanded that their thoughts should be gauged by objective realities。 Hence there arose a succession of great geometers； and their conceptions were applied to the construction of new mechanical contrivances on the one hand； and to the elaboration of theories of sidereal mechanics on the other。 The wonderful company of men who performed the feats that are about to be recorded did not all find their home in Alexandria； to be sure； but they all came more or less under the Alexandrian influence。 We shall see that there are two other important centres； one out in Sicily； almost at the confines of the Greek territory in the west； the other in Asia Minor； notably on the island of Samosthe island which； it will be recalled； was at an earlier day the birthplace of Pythagoras。 But whereas in the previous century colonists from the confines of the civilized world came to Athens； now all eyes turned towards Alexandria； and so improved were the facilities for communication that no doubt the discoveries of one coterie of workers were known to all the others much more quickly than had ever been possible before。 We learn； for example； that the studies of Aristarchus of Samos were definitely known to Archimedes of Syracuse； out in Sicily。 Indeed； as we shall see； it is through a chance reference preserved in one of the writings of Archimedes that one of the most important speculations of Aristarchus is made known to us。 This illustrates sufficiently the intercommunication through which the thought of the Alexandrian epoch was brought into a single channel。 We no longer； as in the day of the earlier schools of Greek philosophy； have isolated groups of thinkers。 The scientific drama is now played out upon a single stage； and if we pass； as we shall in the present chapter； from Alexandria to Syracuse and from Syracuse to Samos； the shift of scenes does no violence to the dramatic unities。 Notwithstanding the number of great workers who were not properly Alexandrians； none the less the epoch is with propriety termed Alexandrian。 Not merely in the third century B。C。； but throughout the lapse of at least four succeeding centuries； the city of Alexander and the Ptolemies continued to hold its place as the undisputed culture…centre of the world。 During that period Rome rose to its pinnacle of glory and began to decline； without ever challenging the intellectual supremacy of the Egyptian city。 We shall see； in a later chapter； that the Alexandrian influences were passed on to the Mohammedan conquerors； and every one is aware that when Alexandria was finally overthrown its place was taken by another Greek city； Byzantium or Constantinople。 But that transfer did not occur until Alexandria had enjoyed a longer period of supremacy as an intellectual centre than had perhaps ever before been granted to any city； with the possible exception of Babylon。
EUCLID （ABOUT 300 B。C。） Our present concern is with that first wonderful development of scientific activity which began under the first Ptolemy； and which presents； in the course of the first century of Alexandrian influence； the most remarkable coterie of scientific workers and thinkers that antiquity produced。 The earliest group of these new leaders in science had at its head a man whose name has been a household word ever since。 This was Euclid； the father of systematic geometry。 Tradition has preserved to us but little of the personality of this remarkable teacher； but； on the other hand； his most important work has come down to us in its entirety。 The Elements of Geometry； with which the name of Euclid is associated in the mind of every school…boy； presented the chief propositions of its subject in so simple and logical a form that the work remained