Brave Little Denis by Mary Louisa Molesworth

He drew on his little dressing-gown, for he was shivering with cold and excitement. But his slippers he would not put on. 'I can run so much faster without them,' he said, speaking to himself in a low voice. Then he opened the door, crossed the little anteroom, and hesitating a moment, threw open the large door of the gallery. An instant he waited before he found courage to look up. Then he did so, with a half-acknowledged feeling that if anything _too_ appalling met his eye, he could still rush back into the shelter of his own room.

But all was still, strangely still, and the curious effect of the moonlight, streaming in, in fitful patches through the coloured windows, for a moment made him forget his fears in a sort of awe-struck admiration. It was even stranger than Linda had described it, for the clouds quickly rushing across the moon, caused a mixture of light and shadow, coloured by the tints of the glass, like broken and confused rainbows. And had Denis not been too frightened to look at the faces on the wall, the effect of this jumble of light and colour and shadow would have been almost comical.