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18 yet millions more would not visibly enlarge the furnace.

To understand the relative position of the stations at which we have stopped in our excursion, it is necessary to assign a scale. If, then, we call the distance of the earth to the sun one mile, the distance of Neptune will be thirty miles; and our nearest neighbour, the moon, will only be four yards from us. To expand this scale to represent the reality, we have only to keep in mind that a railway train, going at the rate of thirty miles an hour, and travelling day and night, would take twenty thousand years to go straight across the whole breadth of the solar system.

But, after all, this journey is nothing more than a morning drive to the houses of a few friends in the neighbouring streets. We have still an expedition before us, which may be compared to the crossing of the Atlantic, or a voyage to China. We have not yet really left home, and now that we propose going abroad, what vehicle shall we take to aid us in our flight to other systems? The comet is all too slow for our purpose. We must have something still more subtle and swift. The only physical agency that can serve our purpose is a ray of light. On a ray of light we may reach the moon in a single second, and the sun in eight minutes. Instead of taking twenty thousand years, like the railway train, to cross the solar system, it would require only eight hours. Let us suppose, then, that, with the ethereal vehicle of light