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454 two, will come in sight. So much the less risk of clouds : and everywhere there may be one, except when it is cloudy. Neither need be more than four thou- sand miles off; so much the larger and more beautiful will they be. If on the old Thornbush moon old Herschel with his reflector could see a town- house two hundred feet long, on the Brick Moon young Herschel will be able to see a dab of mortar a foot and a half long, if he wants to. And people with- out the reflector, with their opera-glass- es, will be able to see sufficiently well." And to this they agreed : that eventu- ally there must be two Brick Moons. Indeed it were better that there should be four, as each must be below the horizon half the time. That is only as many as Jupiter has. But it was also agreed that we might begin with one.

Why we settled on two hundred feet of diameter I hardly know. I think it was from the statement of dear John Farrar's about the impossibility of there being a state house two hundred feet long not yet discovered, on the sunny side of old Thornbush. That, somehow, made two hundred our fixed point. Besides, a moon of two hun- dred feet diameter did not seem quite unmanageable. Yet it was evident that a smaller moon would be of no use, unless we meant to have them near the world, when there would be so many that they would be confus- ing, and eclipsed most of the time. And four thousand miles is a good way off to see a moon even two hundred feet in diameter.

Small though we made them on paper, these two-hundred-foot moons were still too much for us. Of course we meant to build them hollow. But even hollow there must b some thick- ness, and the quantity of brick would at best be enormous. Then, to get them up ! The pea-shooter, of course, was only an illustration. It was long after that time, that Rodman and other guns sent iron balls five or six miles in distance, say two miles, more or less, in height.

Iron is much heavier than hollow brick, but you can build no gun with a bore of two hundred feet now, far less could you then. No. Q. again sug- gested the method of shooting off the moon. It was not to be by any of your sudden explosions. It was to be done as all great things are done, by the gradual and silent accumulation of power. You all know that a fly-wheel heavy, very heavy on the circumfer- ence, light, very light within it was made to save up power, from the time when it was produced to the time when it was wanted. Yes ? Then, before we began even to build the moon, before we even began to make the brick, we would build two gigantic fly-wheels, the diameter of each should be " ever so great," the circumference heavy beyond all precedent, and thun- dering strong, so that no temptation might burst it. They should revolve, their edges nearly touching, in oppo- site directions, for years, if it were ne- cessary, to accumulate power, driven by some waterfall now wasted to the world. One should be a little heavier than the other. When the Brick Moon was finished, and all was ready, IT should be gently rolled down a gigantic groove provided for it, till it lighted on the edge of both wheels at the same instant. Of course it would not rest there, not the ten-thousandth part of a second. It would be snapped upwards, as a drop of water from a grindstone. Upward and upward ; but the heavier wheel would have deflected it a little from the vertical. Upward and north- ward it would rise, therefore, till it had passed the axis of the world. It would, of course, feel the world's attraction all the time, which would bend its flight gently, but still it would leave the world more and more behind. Up- ward still, but now southward, till it had traversed more than one hundred and eighty degrees of a circle. Little resistance, indeed, after it had cleared the forty or fifty miles of visible atmos- phere. "Now let it fall,' : said O., in- spired with the vision. " Let it fall, and the sooner the better ! The curve it is now on will forever clear the world ;