[1.1.18] Let's have another example. You must have seen a silica stone before, of which glass is produced. Let such a rough silica stone, just like its descendant, the glass, the rays pass through unhindered? O no, this you know very well. Why does such a rough silica stone not let the rays through? Because its parts are still too much separated and too little united. If the rays would fall upon it, every little part would devour the rays for himself and will leave nothing, or in a sense only the waste of the absorbed light for his neighbor. But how is it that his descendant, the glass, becomes so generous? Look first, the silica stone is crushed and ground. This way each particle in a sense dies for the other or gets completely separated from the other. Then the silica powder gets washed, then dried, mixed with salt and then put into the furnace where the separate particles become completely mutually united through the salt and the correct temperature of the fire.