20 HISTORY OF SCIENCE. 



of philosophy. Besides, in all ages science and philosophy have reacted 

 upon each other, so that it would be impossible to trace the history of 

 either as an independent line of intellectual advancement. 



The first philosopher who took a point of view entirely subjective was 

 PROTAGORAS (c. B.C. 480 41 1), an Abderite, and a pupil of Democritus. 

 His starting-point was not the material or object world, but the mental 

 or subjective world. He regarded matter as something in itself quite 

 indefinite, something which in its perpetual change and flow appeared 

 now to be this, now to be that. He took no account of the atoms of 

 his master. He declared that things are but what they appear, and 

 that they have for us no other meaning. His great maxim was "man 

 is the measure of all things." By this expression he gave prominence 

 to the view that we can know of the external world nothing beyond 

 its phenomena, and that it is impossible to arrive at any knowledge 

 of things absolutely, or as they are in themselves. 



We may here notice the opinions of the great moralist SOCRATES (B.C. 

 470 400) on physical science, to which in his youngerdays he had given 

 some attention. He declared that it was impossible for men to arrive 

 at any satisfactory knowledge of such things ; for, said he, those who 

 have devoted themselves to investigations of natural laws have come to 

 the most contradictory conclusions. He held also that all such know- 

 ledge was vain and useless, for even if the natural philosophers should 

 succeed in discovering the laws of natural phenomena, they would not 

 be able at will to produce wind or rain or changes of the seasons. He 

 considered, too, that such inquiries were not free from impiety towards 

 the gods. Socrates made " man the measure of all things " in a sense 

 different from that of Protagoras, for he believed that the motions of 

 the sun, moon, and stars are arranged for the convenience of man, for 

 whose benefit also animals, such as goats, sheep, horses, and oxen, are 

 specially designed. 



PLATO (B.C. 427 374), whose name is so illustrious in philosophy, 

 has directly and indirectly largely influenced the course of intellectual 

 development and scientific thought. Before Plato had become the 

 disciple of Socrates, he had been a student of the philosophy of 

 Heraclitus, one of whose prominent doctrines was that all things are 

 in a state of ceaseless change, so that, for example, no one could ever 

 be twice on the same river, inasmuch as the water is ever changing. 

 About the age of twenty Plato became a disciple of Socrates, and 

 continued so until the death of the latter, nine years afterwards. Plato 

 then visited various countries, as Egypt, Persia, Sicily, and Italy. On 

 returning to Athens he established his renowned school of philosophy 

 amid the groves of Academus, near Athens ; and this place has given 

 a common title to schools of art, learning, and science throughout the 

 world. Plato lived to an advanced age, and left behind him many 

 writings, now esteemed amongst the most precious legacies that anti- 

 quity has bequeathed to us. 



