"Teacher proved to us that the bottle is not empty," he added. "He had a bottle which looked to be empty, and he pressed it, mouth downwards, as far as he could, into a large bowl of water.
"While he held it there, he made us notice that the water would not enter very far into the mouth of the bottle. The water in the neck of the bottle was not so high as the water in the basin outside.
"He told us that if the basin were deep enough, we might press the bottle down ever so far, but it would not be possible to fill it with water.""Yes, but he did fill it though at last," said Will. "He slanted the bottle on one side, and then there was a gurgling sound, and the water rushed in.""What do you think made the gurgling sound, Norah?" asked Fred. "Watch, while I do it now with this bottle. As I slant the bottle in the basin of water, something seems to come bubbling up out of it through the water, and now we can see that the bottle is full of water.
"That something that bubbled up was air. It was the air in the empty bottle that prevented the water from rising to fill it. The water could not enter the bottle, because it was already full of something else, and that something else was air.
