This great progress they owed chiefly to one very wonderful invention, to the art of preserving their spoken words and their ideas for the benefit of their children and grandchildren. We call this the art of writing. We are so familiar with writing that we can not understand how people ever managed to live without books and newspapers and magazines. But they did and it was the main reason why they made such slow progress during the first million years of their stay upon this planet. They were like cats and dogs who can only teach their puppies and their kittens a few simple things (barking at a stranger and climbing trees and such things) and who, because they can not write, possess no way in which they can use the experience of their countless ancestors. This sounds almost funny, doesn't it? And why make such a fuss about so simple a matter? But did you ever stop to think what happens when you write a letter? Suppose that you are taking a trip in the mountains and you have seen a deer. You want to tell this to your father who is in the city. What do you do? You put a lot of dots and dashes upon a piece of paper--you add a few more dots and dashes upon an envelope and you carry your epistle to the mailbox together with a two-cent stamp. What have you really been doing? You have changed a number of spoken words into a number of pothooks and scrawls. But how did you know how to make your curlycues in such a fashion that both the postman and your father could retranslate them into spoken words? You knew, because some one had taught you how to draw the precise figures which represented the sound of your spoken words. Just take a few letters and see the way this game is played. We make a guttural noise and write down a "G." We let the air pass through our closed teeth and we write down "S." We open our mouth wide and make a noise like a steam engine and the sound is written down "H." It took the human race hundreds of thousands of years to discover this and the credit for it goes to the Egyptians. Of course they did not use the letters which have been used to print this book. They had a system of their own. It was much prettier than ours but not quite so simple. It consisted of little figures and images of things around the house and around the farm, of knives and plows and birds and pots and pans. These little figures their scribes scratched and painted upon the wall of the temples, upon the coffins of their dead kings and upon the dried leaves of the papyrus plant which has given its name to our "paper." But when the Romans entered this vast library they showed neither enthusiasm nor interest. They possessed a system of writing of their own which they thought vastly superior. [Illustration: THE KEY OF STONE]