CH. I. THALES-ANAXIMANDER. 9 the day was short and the night long. This went on for a few days, and because the sun stood at the same height every day, the name of winter sol-stice, or sun-standing, was given to these days in the middle of winter. Afterwards the sun began to rise a very little higher every day, till in three months, when winter had passed away and the plants and trees began to bud, the sun took exactly twelve hours to pass across the sky from sunrise to sunset, so then the day was twelve hours long, and the night also twelve hours; this was called the spring equi-nox, or equal night, meaning that the day and night were of equal length. After this the sun still rose higher every day, and in three months more stood for some days nearly overhead at mid-day, thus making a long journey from sunrise to sunset, and causing the day to be long and the night short. This was the summer solstice. Then the sun began to rise less high every day, and in another three months there was again equal day and equal night-the autumn equinox had arrived. Finally, in another three months, the shortest day arrived again, and the whole round began afresh. This was how Thales marked out the solstices and the equinoxes; we still call them by the same name as he did, and you may watch these changes of the sun in the sky for yourself. Thales knew that the sun and stars were not gods, and thought they were made of some fiery substance; he knew also that the moon receives its light from the sun and reflects it like a looking-glass. He was very learned in mathematics, and invented several problems now found in the 'Elements of Euclid.' He is also said to have foretold an eclipse, but this is probably not true, as it requires more knowledge than he is likely to have had. Anaximander of Miletus, 610 B.C., the friend of Thales, was the next Greek who made some important discoveries in science. He invented a sun-dial, by making a flat metal plate with the hours of the day marked upon it in a certain order, so that a large pin, or style as it is called, standing in the middle of the plate, cast a shadow on the right hour whenever the sun shone upon it. as the sun is low down in the morning and gradually passes overhead during the day, it will cause the pin to throw its shadow in a different direction at different hours. You can understand that In this way Anaximander taught the Greeks to measure the time of day. He is also said to have been the first astronomer who understood why we see the bright face of the moon growing from a crescent to a full moon and then diminishing again. To know this he must also have known that the moon moves round the earth every month. You can imitate the changes of the moon if you take a round stone and hold it just above your head between you and the sun; you will then have its shady side towards you; pass it slowly round your head, you will find that you see first a bright edge appearing, then more and more of the bright side, till when the stone is on one side of your head and the sun the other, you will see the whole of one side of the stone reflecting the sun's light-this is a full moon. Pass it on slowly round, and you will see this bright side disappear gradually till you bring it back to its old position between you and the sun, when it will be again dark. This is what the moon does every month, producing what are called the phases of the moon. Anaximander also made a map of the world, or at least of as much of it as was known in his time. Pythagoras, one of the most celebrated of the learned. men of Greece, is the next who tells us anything about science. The time and place of his birth is uncertain, but he lived CH. I. PYTHAGORAS ON GEOLOGY. II somewhere between 566 and 470 B.C. He travelled in Egypt, and learnt much there, and afterwards settled at Tarentum, in Italy, where he founded a famous sect called the Pythagoreans. You will read of the opinions of Pythagoras in books of philosophy, but we are only concerned with what he taught about nature. He was the first to assert that the earth was not fixed, but moved in the heavens, but he did not know that it moves round the sun. He also discovered that the evening and morning star are the same planet; he called this planet Eosphorus, for it did not receive the name of Venus till some time afterwards. Some of the most remarkable truths taught by Pythagoras were about geology, or the study of the earth. He noticed that seashells were sometimes to be found far inland imbedded in solid ground in a way that showed they were not brought there by man. Therefore, he argued that to bury sea-shells in the rocks, the sea must once have been there. He had also probably watched the sea eating away the cliffs on the shores of Italy, as you may see it doing now on the shores of Norfolk and Suffolk; and when he was in Egypt he must have seen the Nile carrying mud and laying it down at its mouth, or delta, to form new land. From all these and other observations he, and his pupils who followed him, drew some very true conclusions which are given in Ovid's Metamorphoses' : 1. Solid land has been converted into sea. 2. Sea has been changed into land. Marine shells lie far distant from the deep. 3. Valleys have been excavated by running water, and floods have washed down hills into the sea. 4. Islands have been joined to the mainland by the growth of deltas and new deposits, as in the case of Antissa joined to Lesbos, Pharos to Egypt, &c. 5. Peninsulas have been divided from the mainland and have become islands, as Leucadia; and according to tradition Sicily, the sea having carried away the isthmus. 6. Land has been submerged by earthquakes; the Gre cian cities of Helice and Buris, for example, are to be seen under the sea, with their walls inclined. 7. There are streams which have a petrifying power, and convert the substances which they touch into marble. 8. Volcanic vents shift their position; there was a time when Etna was not a burning mountain, and the time will come when it will cease to burn. These, and other sentences of the same kind, show how carefully Pythagoras and his followers must have observed nature, for the changes that are going on upon the earth take place so very slowly that it is only by very careful comparison that we can prove they are happening at all. Pythagoras was the first man who was called a philosopher, or lover of wisdom. He made many discoveries about musical notes, and succeeded in stretching strings so that when struck they gave the right notes of the octave in succession. CH. II. ANAXAGORAS STUDIES the MOON. 13 CHAPTER II. 499 TO 322 B.C. Anaxagoras studies the Moon-Describes Eclipses of the Sun and Moon-Is Tried and Condemned for Denying that the Sun is a God-Hippocrates the Father of Medicine-Separates the Office of Priest and Doctor-Studies the Human Body-Eudoxus has an Observatory-Makes a Map of the Stars-Explains the Movements of the Planets-Democritus Studies the Milky Way-Aristotle an Astronomer and Zoologist-Divides Animals into Classes-Teaches that there is a Gradual Succession of Animal Life-Studies the Difference of the Life in Plants and Animals. Anaxagoras, who was the next great teacher after Pythagoras, was born in Ionia about 499 B.C., but he went when quite young to Athens. He loved to study nature for its own sake, and was once heard to say that he was born to contemplate the sun, moon, and heavens. Although there were no telescopes in those days, he managed to observe that there were mountains, plains, and valleys in the moon. He believed it to be a second earth, perhaps with living beings in it. He did not know, as we do now, that the moon has no atmosphere round it, such as living beings like ourselves require in order to breathe. He discovered that an eclipse of the sun is caused by the moon coming directly between the earth and the sun, and an eclipse of the moon by the earth coming between the moon and the sun. When the moon comes exactly between our earth and the sun, we see the moon's dark body pass over the sun, so as to |