"With a piece of ice."
"What? Do you think that would do?"
"Why not? All that is needed is to collect the sun's rays into one common focus, and ice will serve that purpose as well as the finest crystal."
"Is it possible?" said Johnson.
"Yes, only I should like fresh water ice, it is harder and more transparent than the other."
"There it is to your hand, if I am not much mistaken," said Johnson, pointing to a hummock close by.
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"I fancy that is fresh water, from the dark look of it, and the green tinge."
"You are right. Bring your hatchet, Johnson."
A good-sized piece was soon cut off, about a foot in diameter, and the Doctor set to work. He began by chopping it into rough shape with the hatchet; then he operated upon it more carefully with his knife, making as smooth a surface as possible, and finished the polishing process with his fingers, rubbing away until he had obtained as transparent a lens as if it had been made of magnificent crystal.