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lenses instead of two only; we can then arrange to get quite a large picture with no fuzziness anywhere.

Let me now tell you a little about some of the largest lenses in the world. They have nearly all been made by an American firm called Alvan Clark. It would have been nicer for us to say that they were made in England: we have, however, the satisfaction of knowing that an Englishman, the Rev. W. R. Dawes, was chiefly instrumental in drawing attention to the excellent workmanship of the Clarks: so that when a big telescope was to be made, the order was placed with them. One of their first successes was a 26-inch lens built for the Washington Observatory; and almost directly it was pointed to the heavens, two tiny moons of the planet Mars were discovered with it. Up to that time Mars was believed to have no satellite: When in 1832 Tennyson was writing the "Palace of Art," he put in some astronomical verses, including the line—

"She saw the snowy poles of moonless Mars,"

but these verses were left out of the poem, and not published until 1898, when two moons had been discovered, so that the line was altered to

" She saw the snowy poles and moons of Mars."

Another interesting thing about these moons is that Dean Swift jokingly predicted them in his Gulliver's Travels. He speaks of the astronomers of Laputa as having

"discovered 2 lesser stars or satellites which revolve about Mars."