It was there that he tried to read the book.

The words were very long and most difficultly spelt.
But he did manage to make out that all dragons sleep for one hour after sunset.

Then he heard a loud rattling sound from the ruin, and he knew it was the dragon who was making that sound, so he looked through the field-glasses, frowning with anxiety to see what the dragon was doing.
And as he looked he started and almost dropped the glasses, and the frown cleared away from his forehead and he gave a sigh that was almost a sob and almost a laugh, and then he said 'That old thing!' Then he looked again, and this is what he saw.

An enormous green dragon, very long and fierce-looking, that rattled as it moved, going in and out among the ruins, rubbing itself against the fallen pillars.

And the reason Philip laughed and sighed was that he knew that dragon very well indeed.