But it is not merely as thus explaining what had been a most perplexing problem that I have dealt with the evidence supplied by the practical identity of these five comets’ orbits.  When once we recognize that this, and this only, can be the explanation of the associated group of five comets, we perceive that very interesting and important light has been thrown on the subject of comets generally.  To begin with:  what an amazing comet that must have been from which these five, and we know not how many more, were formed by disaggregative processes—­probably by the divellent action of repulsive forces exerted by the sun!  Those who remember the comets of 1843 and 1882 as they appeared when at their full splendor will be able to imagine how noble an appearance a comet would present which was formed of these combined together in one.  But the comet of 1880 was described by all who saw it in the southern hemisphere as most remarkable in appearance, despite the faintness of its head.  The great southern comet of the present year was a striking object in the skies, though it showed the same weakness about the head.  That of 1668 was probably as remarkable in appearance as even the comet of 1882.  A comet formed by combining all these together would certainly surpass in magnificence all the comets ever observed by astronomers.

And then, what enormous periods of time must have been required to distribute the fragments of a single comet so widely that one would be found returning to its perihelion more than two centuries after another!  When I spoke of one member of the Biela group being in aphelion when another would be in perihelion, I was speaking of a difference of only three and one-third years in time; and even that would require thousands of years.  But the scattered cometic bodies which returned to the sun’s neighborhood in 1668 and 1887 speak probably of millions of years which have passed since first this comet was formed.  It would be a matter of curious inquiry to determine what may have been the condition of our sun, what even his volume, at that remote epoch in history.

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THE ISOLATION OF FLUORINE.

The element fluorine has at last been successfully isolated, and its chief chemical and physical properties determined.  Many chemists, notably Faraday, Gore, Pflaunder, and Brauner, have endeavored to prepare this element in the free state, but all attempts have hitherto proved futile.  M. Moissau, after a long series of researches with the fluorides of phosphorus, and the highly poisonous arsenic trifluoride, has finally been able to liberate fluorine in the gaseous state from anhydrous hydrofluoric acid by electrolysis.  This acid in the pure state is not an electrolyte, but when potassium fluoride is dissolved in it, a current from ninety Bunsen elements decomposes it, evolving hydrogen from the negative and fluoride from the positive electrode.