of the immense number of cometic voyages through space, when our sun, one amongst millions of millions of suns, is visited by so many comets, that Kepler (before the telescope had shown the real wealth of comet-matter) said that the comets of the solar system must be as the fish of the sea for multitude? Every comet reaching our system indicates the existence of comets reaching or voyaging towards other systems than ours. We must picture the interstellar spaces, which seem wholly unoccupied, as in reality tenanted by millions of comets. for each one of the millions on millions of suns. This opinion, indeed, is forced upon us whatsoever view we take as to the past history of individual comets. A wonderful wealth of matter is thus displayed to us. The whole universe is presented as a scene of amazingly complex activity; and to the wonder caused by its infinite extent and by the vastness of the orbs which people it, there are added the thoughts suggested by the amazing voyages which the messengers, as it were, from one scheme to another are continually making, and by the enormous duration of each single voyage.

But we have still to consider whence comets come. We may trace them through voyage after voyage, but that does not bring us to their starting-place. We have still to enquire how these strange objects came into existence. The enquiry may not indeed be successful, since it carries us back to epochs so remote that we may well shrink from endeavouring to ascertain what then was

taking place. Nevertheless, modern science teaches us this lesson above all others, that there is nothing old as there is nothing new in the universe-that is, that no process or state is completely passed, and that no process or state now appears for the first time. We will then, in another chapter, make a survey of the domain of science, 'bringing forth things old and new' for comparison with what is known about comets, in order that, if it be possible, we may form some idea of the origin of these mysterious objects. It may be that we shall find evidence not altogether indistinct or unsatisfactory to show that in our time and, as it were, under our very eyes comets are being brought into existence. Need it be said that if this is so, it is to our sun that we shall have to look for the processes by which comets are being generated, and the materials from which they are being formed?

WHENCE COME THE COMETS?

WHAT I propose to say in this chapter will probably surprise many readers of these pages. It may seem to them that the ideas I am about to suggest are too wild and fanciful for acceptance. Yet before our enquiry begins let us recall to mind the wonderful and mysterious facts which have been learned respecting comets, and remember that the real explanation of those facts cannot but be surprising. Here are these amazing objects often exceeding the sun himself many times in size, spreading their huge tails over distances measured by millions of miles, undergoing the most wonderful changes of shape and dimensions, actuated apparently by forces quite different in their nature from the force of gravity and far more potent in their action, travelling from the interstellar spaces after voyages of incalculable duration, and lastly-most wonderful of all perhaps returning into those far-distant spaces after subserving no useful purpose, so far as can be perceived, in the economy of our solar system. What can these objects be but wonderful? What theory can explain them but one that is as wonderful in its nature as the objects it is to account for? We

are in the presence of stupendous facts, and we must not therefore be surprised if bold and startling ideas are suggested in explanation of those facts.

Two circumstances have recently aided speculation in this difficult and perplexing subject. One is the recognition, by means of the spectroscope, of the gaseity of the head and coma (or hair) of comets. The other is the discovery of an association between comets and meteorsystems. On the first fact I shall say little, because it rather promises future explanation than in itself affords sufficient evidence on which to base any opinion respecting comets. Doubtless when some splendid comet-like that with the aigrette-plume in 1858, known as Donati's, and the wonderful object which in the summer of 1861 shone for a few days above the horizon during the morning hours-shall have been subjected to careful spectroscopic analysis, we shall begin to know something respecting the actual structure and condition of cometic appendages. But for the present the most effective piece of knowledge in our possession is that which indicates a connection between meteors and comets.

Briefly stated, the fact-now perfectly demonstratedis this: The only meteor-systems whose paths have been recognised are found to travel in the track or orbit of known comets. We cannot tell quite certainly what may be the nature of the connection thus indicated; but it would seem to be tolerably obvious that the meteors or falling stars which are seen for a few brief moments as

they are fired during their rush through our upper air are bodies scattered on the track of comets by some process of dispersion the nature of which may one day be ascertained. And this view seems to be confirmed by Sir John Herschel's observations of the comet of 1862, which not only showed the very kind of appearances we should expect on this theory, but is otherwise remarkable as being the only bright comet yet unquestionably associated with one of our recognised meteor-systems-it is the parent comet, in fact, of the famous August meteors, called also the 'Perseids,' and sometimes the Tears of St. Lawrence.'

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Now, Sir John Herschel, before it had been demonstrated that the comet is thus connected with the August meteors, recorded the following observations which he had made upon it :-The phenomena exhibited by its nucleus and head were peculiarly interesting and instructive, it being only on very rare occasions that a comet can be closely inspected in the very crisis of its fate, so that we can witness the actual effect of the sun's rays upon it. In this case the pouring forth of the cometic matter from the singularly bright and highly condensed nucleus took place in a single compact stream, which, after attaining a short distance, equal to rather less than a diameter of the nucleus itself, was so suddenly broken up and dispersed as to give on the first inspection the impression of a double nucleus. The direction of the jet varied considerably from day to day, but always declined more or less from the exact direction from the sun.' It appears clear