Page:The fairy tales of science.djvu/239

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brother of 1744, for instance, had no less than six, spread out like an immense fan, extending to a distance of nearly 30 degrees in length. I have just now mentioned that my brother of 1811 was not at first provided with an appendage of luminous vapour. This is often the case with us. Thus the great Comet of 1843 showed at its first appearance simply a nucleus, surrounded by a coma; but it speedily set about supplying the deficiency, and in less than twenty days managed to throw out a most magnificent tail, measuring two hundred millions of miles, which was generated, accordingly, at the rate of 10,000,000 miles a day, the matter composing it being propelled through space with a velocity of 115 miles per second, which is nearly six times that of the earth in its orbit, and two hundred and fifty times greater than that of a cannon-ball!

You are already aware, so I need hardly tell you, that we are all of our family most eccentric in our motions. To superficial observation we would indeed seem to be careering with mad capriciousness along the great highway of space. But if you watch our motions more closely, you will find that there is the strictest method in this apparent madness of our movements, and that we obey the same universal law of attraction and gravitation as the other celestial bodies—some of us moving about the sun in parabolic orbits, or at least in ellipses of various degrees of eccentricity, and returning in determinate periods in the same path (unless dis-