There was always a sentimental streak in George. "I can't help thinking that is the most beautiful flag in the world; I suppose other people think the same of their flag. How did flags come to be used by people?"
"The flag is the successor of the banner, which is taken from the Celtic word 'band.' The Bible mentions banners, showing they were used early in scriptural history. The banners of the Romans, used in their warfares, were essentially different from modern flags, colors and ensigns; they were carvings of wood or metal, some of them representing eagles, like the Persian standard described by Xenophon. In the Middle Ages it was a connecting link between the military and the clergy. The crescent and the cross symbols typified the two great contending forces of the world at that time."
Returning to their home, tired with the exertions, they sat in the living room and talked over the events of the day. Somehow, they felt that the day was too sacred to be desecrated with further toil. They congratulated each other at the success in raising the pole, as that was a matter which had given them a great deal of concern.
Ever since the day on which they commenced work on the electric battery the boys deplored the lack of glass. If they could make that it would be of such immense importance to them in many ways. It would be of great service for their tableware; they could use it for their electric work, which interested them more than any branch to which their time had been given, among the mechanical arts; with that they could make thermometers and testing instruments; and give their house the air of a modern home, because windows could be put in.
"Will it be difficult to make glass?" asked George.
"It is an exceedingly simple matter to make glass—that is, to fuse or melt it. The difficult part is the art of making it, either by the blowing process, or by making the flat forms, like window panes and the like. Owing to the simplicity in preparing it, the making of glass articles was known at a very early date, certainly fifteen hundred years before the beginning of the Christian era. In the first stages only opaque glass was produced, and it was not until eight hundred years later that the first transparent product was manufactured. Under Pharaoh it was one of the products extensively made and exported to Phonecia and other Mediterranean ports. Five hundred years before Christ, Aristophanes mentions glass or crystal vessels, but as its value at that time was next to gold it could not have been a common article."
"What is glass made of?"
"Simply common sand. Sand is the ground up particles of quartz, and may be found almost everywhere. The principal thing is to get the pure quartz. In connection an alkali of some kind must be used."
"What is an alkali?"
"A substance which is the exact opposite of an acid. Potash, soda and hartshorn (or ammonia) are the best known. They have most remarkable chemical activities, and an alkali united with an acid entirely neutralizes or destroys the activity of both. The compound produced by the union of an acid and an alkali is termed a salt."