“It must act somehow,” said Jack.
“Is it the light?” said Ned.
“But light blackens the skin, or heat does,” reasoned Dick.
“The true cause is curious. It is an action of light through the eyes, and thence, by the brain pathways, on to the numberless little pigment-cells of the skin, which are able to shrink or enlarge, and thus change the hue of the whole outside of the fish. Blind fish do not change their hue.”
“But that is not the way we get brown,” said Rose.
“No, not at all. Sun-tan is not caused by the sun’s heat; it is an effect of the chemical rays.”
“A kind of photography, Pardy?”
“Yes, more complete than you can fancy; the sunlight falls nowhere without leaving a record, only we cannot recover it as we can the photograph of the camera. In fact, it is probable that every reflection from everything and onto everything leaves positive records. It was Professor Draper, I think, who played with this pretty idea, that, if we had the means of development, we might thus win back pictures of every event since the world was made.”
“I like that,” said Anne. “What would one desire to see if we could recover these lost memorials?”
There was a little pause at this.