ANCIENT SCIENCE. 29 



that the motion which naturally belongs to the whole belongs to each 

 of the parts. But the order of the world is eternal, and therefore no 

 violent or contra-natural motion can have a place in this order." 

 Though Aristotle thus denies motion to the earth, he contends that 

 its form is spherical, and in the proof he advances an argument still 

 used, namely, the figure of the shadow cast on the moon in her eclipse. 

 He also asserts that bodies do not fall towards the earth in lines which 

 are parallel at different places. That the magnitude of the earth is 

 not great he proves by the change in the appearance of the starry sky 

 when the observer changes his position ; for when we go to the north, 

 stars which are visible in Egypt cease to appear, and others, which in 

 Egypt rise and set, remain always above the horizon. The circum- 

 ference of the earth, he says, had been calculated by some geometers, 

 who had estimated it to be 400,000 stadia. 



Among the writings of Aristotle is a treatise on Mechanical Pro- 

 blems, and his treatment of a very elementary question will at once 

 illustrate his system, and exhibit the condition of the science in his 

 time. The problem was to give a reason why a lever or balance with 

 arms of unequal length keeps unequal weights in equilibrium. Aris- . 

 totle states that the explanation is to be found in the properties of the 

 circle, and of these properties he proceeds to give an enumeration,, 

 remarking finally that it could not be surprising that a figure which 

 possessed so many wonderful properties should have also another one 

 in the balancing of unequal weights. This solution has been admired 

 and developed by Aristotelean philosophers, in spite of its obvious 

 absurdity. Aristotle's treatise is, however, not without some indica- 

 tions of correct notions concerning forces, and in an elementary case 

 the composition of velocities is discussed ; but the reasoning by which 

 the propositions are supported is hardly more satisfactory than that 

 of which specimens have already been given. 



The best work of Aristotle relating to natural science is, perhaps,, 

 his treatise on animals. As he is the first known author of any attempt 

 at a scientific description and classification of animals, he may be con- 

 sidered as the originator of zoology. The treatise just mentioned in- 

 cludes a great number of statements which show indeed that Aristotle,. 

 or others for him, had no lack of ability in observing facts. So many 

 truths regarding the anatomy and dispositions of animals are set down, 

 that some modern authors suppose that the ancient sage must certainly 

 have himself examined and dissected animals of every kind. There 

 is a story, too, about Alexander the Great causing strange animals to 

 be collected in Asia, and sent to Greece for the inspection of Aristotle. 

 Aristotle divides animals into viviparous and oviparous, and under the 

 first he ranks all quadrupeds ; the second comprehending birds, fishes, 

 and insects. It is now well known that such a division is defective, 

 some quadrupeds (e.g., lizards) being oviparous, and some fishes vivi- 

 parous. 



