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comet known as Halley's may be regarded as by far the most interesting of all the comets recorded in history; and this, whether looked at from the standpoint of the historian or of the astronomer; and having regard to the position which it has occupied during many centuries in the public mind, and is likely also to occupy during the year 1910, it will be worth while to review its career in some detail.

A few years after the advent of the celebrated Comet of 1680 Sir I. Newton published his epoch-making Principia, in which he first promulgated the Theory of Gravitation, and applied it to the orbit of that comet. He explained the