To return again to the era of the first calendar. While the wise men of Mesopotamia were engaged in mingling science and mystery, another civilization, the Egyptian, was developing upon the banks of the Nile and passing through much of the same stages. In due course the Persians conquered both Mesopotamia and Egypt and absorbed their knowledge. Still later the wonderful Greek nation combined astronomy with mathematics in a way which makes us wonder to this day. This is the way in which civilization has grown. Race after race, during century after century has added its new knowledge and discoveries to that which has been learned before. It is interesting to note that the astronomy of the Babylonians appears to have been paralleled independently by other ancient civilizations between which there was no apparent possibility of intercourse. The Chinese in the East and the Aztecs of Mexico, on the other side of the world, invented practically the same astronomical instruments as the Babylonians and made similar discoveries. All methods of indicating time have been steps upon the long road which has led to the making of modern timepieces. The progressive Greeks did not permit knowledge to be monopolized by the priesthood and probably their common people knew more about the stars than most of the population of America do to this day. Sailors possessed no compasses, but they voyaged very skilfully with the guidance of the stars, while farmers, lacking our modern weather-reports and crop-bulletins, learned to govern their planting and harvesting by the positions of the heavenly bodies. In one sense, this is time-telling and in another it is not, but our ideas of time and astronomy have always been so closely associated that it is hard to think of one apart from the other. This is because the movements of the earth, which produce night and day and the changes of the seasons, are our supreme court of time, our final standard for its measurement. And since we cannot see the earth move, we judge of its motion by the apparent movement of the heavenly bodies, just as we realize the movement of a train by watching the landscape rush past us as we go.