Now the breadth of the spectrum seen by Dr. Huggins, corresponded with the breadth of the coma so far as the widest parts of the tongue-shaped bands were concerned. But the narrower parts were about the width of the nucleus. Therefore the first question to be decided was this,-Is the narrowing of these bands of light towards one extremity, and of the other towards both extremities, to be considered as indicative of any difference, in character, between the light emitted by the nucleus and that emitted by the coma ? At first sight it seems that no other conclusion could be come to. But a little consideration enabled Dr. Huggins to arrive at a different result. The tongue-shaped bands were not only narrower but very much fainter towards one end. They were also fainter along their outer edges, on account, of course, of the faintness of the coma as compared with the nucleus. Now it was possible that the narrowing down of the bands might be only apparent, and due to the fact that their outer parts, though really existent, became invisible at the fainter end. And there were two modes of attacking the question. First the observer could determine by a careful inspection whether the light at the narrower end of the tongues was so faint that it ought to disappear at the edges merely by undergoing the same sort of reduction as the brighter light at the broader end of the tongue : this would show that the coma does not differ in constitution from the nucleus. Secondly, if the strip brought under examination were narrowed by any contrivance, it is clear that any difference which might exist in the constitution of the coma and of the nucleus ought to be exhibited in a more marked manner.

1 Our readers will, of course, understand that a slice only of the object is brought under spectroscopic analysis at once. If the whole of a circular object, whose centre was gaseous, were examined at once, the middle streak of the spectrum would exhibit the compound spectrum of the edge and centre of the object. Such an arrangement would clearly be unfavourable to the formation of clear views respecting the character of the object's light.

Dr. Huggins applied both methods, and each resulted in showing that the nucleus has the same constitution as the coma, excepting only that the exterior part of the coma seems to give a continuous spectrum. In other words, the nucleus and all the coma except its outer shell consists of the same incandescent vapour; but the outer shell of the coma either consists of incandescent solid or liquid matter or shines by reflecting the solar rays.

So far, however, there is little in the spectroscopic analysis which differs in character from what had been observed respecting Brorsen's comet. But we have now to record one of the most startling discoveries ever made respecting comets.

Dr. Huggins was reminded by the appearance of the cometic spectrum of a form of the spectrum of carbon which he had observed in the year 1864. It must be premised that the spectrum of an element often assumes a different form according to the circumstances under which it is obtained. Amongst the objects which have spectra thus variable is the element carbon. The particular form of carbon-spectrum which resembled that of the comet, is that obtained when an electric spark is taken through olefiant gas-a substance which, as many of my readers are doubtless aware, consists of carbon and hydrogen, and is one of the constituents of ordinary coal-gas.1 Of course the spectrum of olefiant gas exhibits the bright lines belonging to hydrogen; but as these are well known, the part of the spectrum belonging to carbon also becomes determinable.

Having noticed, as we said, the resemblance between the spectrum of the comet and a form of the carbon spectrum, Dr. Huggins determined to compare the two spectra directly. We have not space to explain the contrivances by which this was effected. Suffice it to say, that when the two spectra were brought side by side it appeared that in place of mere resemblance there was absolute identity. The bands of light which formed the comet's spectrum were found not only to coincide in position with those which appeared in the spectrum of olefiant gas, but to present the same relative brightness. Two days later the observations were repeated by Dr. Huggins in company with Professor Miller (who had been associated with him in his earlier spectroscopic labours), and both observers agreed in the opinion that the coincidence between the spectra could not be more exact.

1 The other constituent is 'fire-damp;' also a compound of carbon and hydrogen. Olefiant gas is commonly called heavy carburetted hydrogen, while fire-damp is termed light carburetted hydrogen.

The reader will, of course, understand that the hydrogen lines belonging to the spectrum of olefiant gas are not seen in the spectrum of the comet.

Now only one interpretation can be put on this remarkable result, and that is that Winnecke's comet consists of the incandescent vapour of carbon, - not of burning carbon, be it understood, but of volatilised carbon.

But carbon, as we are acquainted with it on earth, is a substance whose chief peculiarity, perhaps, is its fixity at ordinary temperatures; and no phenomenon hitherto presented by comets is more perplexing than the existence of volatilised carbon as the main or only constituent of a comet of enormous real bulk, when that comet was not so near to the sun as to be raised


(one could suppose) to an extraordinarily high temperature. There have been cases where comets have been so near to the sun as to account for almost any conceivable change in the constitution of their elements. An intensity of heat of which we can form no conception must have been experienced, for example, by Newton's comet; and a still fiercer heat dissipated the substance of the comet of 1843. But Winnecke's comet at the time of observation was at far too great a distance from the sun for us to assign to its mass a temperature which under ordinary circumstances would account for the volatilisation of carbon.