On these blocks she laid a second flooring of short boards, which made the second story.

She then stepped up upon the staging which she had thus built, to see if it was steady.

It was very steady indeed.
"Let _me_ get up on it," said Bella.
Bella accordingly climbed up, and she and Mary Bell danced upon it together in great glee for some time to show how steady it was.
Mary Bell then attempted to open the window.

She found that she could open it a little way, but not far enough to get in.

So she said that she must make one more "story." They then both went back to the pile, and got two more blocks and another board to lay across upon the top of them for a flooring, and when these were placed, Mary Bell found that she could raise the window very high.