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194 been replaced in scientific circles by the term "luminous meteor", or simply "meteor". This summary will suffice as a preface to what is to follow.

In Nov. 1799, and 34 years afterwards, namely, in Nov. 1833, there happened magnificent displays of luminous meteors, radiating from a point in the constellation Leo, whence they have obtained the name of Leonids. Drawing the conclusion, from a catalogue of such displays which had been formed by a Belgian astronomer named Quetelet, that these displays were periodic at stated intervals, an American astronomer named Newton (following up some previous investigations by two learned Americans, Olmsted and Twining, of New Haven, Connecticut) entered upon a thorough investigation of the subject with a view of ascertaining whether any prediction as to future displays could safely be put forth. He came to an affirmative conclusion by announcing that another great display would occur on Nov. 14, 1866; in other words, that these displays were undoubtedly periodic, and that the period was about 33¼ years. The display duly happened as Newton had predicted, and was a very beautiful one; but we are not here concerned with any descriptive details, except to say that a repetition of the show on a much smaller scale occurred in 1867; and that the swarm is so stretched out that it seems to take more than 3 years in passing a given point in its orbit whilst crossing the Earth's orbit. Another great display was expected in 1899 or 1900 but did not occur, though in November 1898 and November 1901 considerable displays did take place.

Taking advantage of the information which had been gathered by previous workers in this field, Professor J. C. Adams, of Cambridge (of Neptune fame), proceeded to calculate elliptic elements for the orbit of the meteor swarm treated as, in a sense, a concrete mass.