I have both editions. There are a number of small differences between them, but the most obvious one is at the end of the Dark Island, which I've put here. I'm not positive which came first. Pardon any typo's.
1: In a few moments the darkness turned into a grayness ahead, and then, almost before they dares to begin hoping, they had shot out into the sunlight and were in the warm, blue world again. And all at once everybody realized that there was nothing to be afraid of and never had been. They blinked their eyes and looked about them. The brightness of the ship herself astonished them: they had half expected to find that the darkness would cling to the white and the green and the gold in the form of some grime or scum. And then first one, then another, began laughing.
"I reckon we've made pretty good fools of ourselves," said Rynelf.
Lucy lost no time in coming down to the deck, where she found the others all gathered round the newcomer. ...[more here, but it's the same in both editions]...
Lord Rhoop fell on his knees and kissed the King's hand. "Sire," he said, "you are the man in all the world I most wished to see. Grant me a boon."
"What is it?" asked Caspian.
"Never to bring me back there," he said. He pointed astern. They all looked. But they saw only bright blue sea and bright blue sky. The Dark Island and the darkness had vanished for ever.
"Why!" cried Lord Rhoop. "You have destroyed it!"
"I don't think it was us," said Lucy.
"Sire," said Drinian, "this wind is fair for the southeast. Shall I have our poor fellows up and set sail? And after that, every man who can be spared, to his hammock."
"Yes," said Caspian, "and let there be grog all round. Heigh-ho, I feel I could sleep the clock round myself."
So all afternoon with great joy they sailed southeast with a fair wind. But nobody noticed when the albatross had disappeared.
2: In a few moments the darkness turned into a greyness ahead, and then, almost before they dared to begin hoping, they had shot out into the sunlight and were in the warm, blue world again. And just as there are moments when simply to lie in bed and see the daylight pouring through your window and to hear the cheerful voice of an early postman or milkman down below and to realise that
it was only a dream: it wasn't real, is so heavenly that it was very nearly worth having the nightmare in order to have the joy of waking, so they all felt when they came out of the dark. The brightness of the ship herself astonished them: they had half expected to find that the darkness would cling to the white and the green and the gold in some form of grime or scum.
Lucy lost no time in coming down to the deck, where she found the others all gathered round the newcomer. ...[same as in other edition]...
Lord Rhoop fell on his knees and kissed the King's hand. "Sire," he said, "you are the man in all the world I most wised to see. Grant me a boon."
"What is it?" asked Caspian.
"Never to ask me, nor to let any other ask me, what I have seen during my years on the Dark Island."
"An easy boon, my Lord," answered Caspian, and added with a shudder. "
Ask you: I should think not. I would give all my treasure
not to hear it."
"Sire," said Drinian, "this wind is fair for the south-east. Shall I have our poor fellows up and set sail? And after that, every man who can be spared, to his hammock."
"Yes," said Caspian, "and let there be grog all round. Heigh-ho, I feel I could sleep the clock round myself."
So all afternoon with great joy they sailed south-east with a fair wind, and the hump of darkness grew smaller and smaller astern. But nobody noticed when the albatross had disappeared.
The version I read for years was the one listed second here. So a couple years ago when I read the first version I was like, "Whooooah, the Dark Island disappeared!" Which was okay in a way, as I always felt Reepicheep wouldn't have been satisfied with sailing away from the Island, but if it was gone he would think that they had somehow conquered it.
On another note, was Rhoop the only living person on the Island?