dition of the matter raised in gaseous form from the nucleus; and if as yet we have had no direct spectroscopic evidence of the existence of iron in comets, we know that meteors are closely connected with comets, and that many meteors contain iron. Moreover, as unexpected spectroscopic evidence of the presence of the substance sodium, common in so many meteors, has been found in the case of one comet, we may fairly hope that under yet more favourable conditions, the presence of iron also may be recognised in the

same way.

How far electricity may be looked to for an explanation of cometic phenomena, is a doubtful point among astronomers and physicists. For my own part, I must confess I share the strong objections which many physicists have expressed against the mere vague suggestion that perhaps this is an electrical phenomenon, perhaps that other feature is electrical too, perhaps all or most of the phenomena of comets depend on electricity. It is so easy to make such suggestions, so difficult to obtain evidence in their favour having the slightest scientific value. Still I hold the electrical idea to be well worth careful study. Whatever credit may hereafter be given to any electrical theory of comets, will be solely and entirely due to those who may help to establish it upon a basis of sound evidence-none whatever to the mere suggestion, which has been made time and again since it was first advanced by Fontenelle. Dr. Huggins says that he finds there is a rapidly growing feeling among physicists that both the inherent light (which he prefers to call the self-light) of comets and the phenomena of their tails belong to the order of electrical phenomena. An American astronomer recently wrote to him, as to American views of the self-light of comets, 'I cannot speak with authority for anyone but myself; still I think the prevailing impression amongst us is that this light is due to an electric, or, if I may coin the word' (far better not) 'an electric-oid action of some kind.' On this Dr. Huggins himself remarks

The spectroscopic results fail to give conclusive evidence on this point; still, perhaps, upon the whole, especially if we consider the photographs of last year, the teachings of the spectroscope are in favour of the view that the self-light of comets is due to electric discharges. Those who are disposed to believe that the truth lies in this direction, differ from each other in the precise modes in which they would apply the known laws of electric action to the phenomena of comets. Broadly, the different applications of principles of electricity which have been suggested, group themselves about the common idea, that great electrical disturbances are set up by the sun's action in connection with the vaporisation of some of the matter of the nucleus, and that the tail is probably matter carried away, possibly in connection with electric discharges, under an electrical influence of repulsion exerted by the sun. This view necessitates the supposition that the sun is strongly electrified, either negatively or positively, and further, that in the processes taking place in the comet, either of vaporisation or of some other kind, the matter thrown out by the nucleus has become strongly electrified in the same way as the sun-that is, negatively if the sun's electricity is negative, or positively if the sun's is positive. The enormous disturbances which the spectroscope shows to be always at work in the sun must be accompanied by electrical changes of equal magnitude, but we know nothing as to how far these are all, or the great majority of them, in one direction, so as to cause the sun to maintain permanently a high electrical state, whether positive or negative.

Unless some such state of things exist, Sir John Herschel's statement That this force' (the repulsive force forming the tail) 'cannot be of the nature of electric or magnetic forces,' must be accepted, for, as he points out, 'the centre of gravity of each particle, would not be affected; the attraction on one of its sides would precisely equal the repulsion on the other.' Repulsion of the cometary matter could only take place if this matter, after it has been driven off from the nucleus and the sun, have both high electric potentials of the same kind. Further, it is suggested that luminous jets, streams, halos, and envelopes belong to the same order of phenomena as the aurora, the electrical brush, and the stratified discharges of exhausted tubes.

All this, it will be noticed, is at present merely hypothetical. It is, however, worthy of notice that outside of

electricity there is nothing known to physicists which seems to afford even a promise of explanation so far at least as the grander and more striking (also the most mysterious) of cometic phenomena are concerned. It may well be that with our advancing knowledge of meteors and meteor systems, the spectroscopic analysis of the next few comets of the larger and completer types-comets like Donati's comet, the great comet of 1811, and the comet of 1861may throw unexpected light on mysteries which still remain among the most profound and unpromising problems presented to modern science.

DANGERS FROM COMETS.

THE appearance of two large comets in 1881, and the discovery of several telescopic comets announced in scientific journals (in 1882 also large comets were seen), have led many to ask whether these objects may be regarded as portents, while others, not quite so ill-informed, have yet fancied that there may be some connection between the comets and the exceptionally warm weather experienced during a portion of the summer. I propose to consider briefly here the ideas commonly entertained respecting the possible influence of comets on terrestrial weather, touching only in passing on the belief, which ought long since to have died a natural death, that comets are sent as signs of approaching misfortunes to the human race.

With regard to the last-mentioned superstition, I should in the first place notice that in former times the belief was natural enough. If we consider the way in which men in past ages regarded the heavenly bodies, we see that whether they considered comets to be members of the heavenly host or to be appearances in the upper air, they had good reasons for regarding them as portentous. Perceiving that the sun and moon, two of the seven planets of their astronomy, exercised very important influences on the earth, the moon ruling the tides and measuring the night, while the changes as well of the circling year with its seasons as of the day with its hours of morning, noon, and evening, were manifestly dependent on the sun's apparent motions, it was natural that they should regard the other planets as similarly influential,

though they were not equally well able to ascertain what special effects each planet produced. Hence arose the system of astrology, a system whose importance to the men of past ages is seldom fully appreciated. In that system the fixed stars found necessarily their place, so that all the heavenly bodies ordinarily seen-sun, moon, planets, and stars were regarded as of extreme importance to the human race, because in their ever-varying positions those bodies were supposed to exert ever-varying influences. If comets were to be looked upon (as by the Chaldeans, whose doctrine was later advocated by Seneca and others) as heavenly bodies, moving like the planets in regular paths, it was natural that to them should be assigned an influence of a special kind, corresponding to the special character of comets in all respects, in their motion, in their appearance, and in their changes of aspect. If, on the other hand, while the heavenly bodies were regarded as above or in the firmament,1

I am satisfied that the doctrine of a firmament-a doctrine which almost all primitive or barbaric science recognises-occupies a most important position in the astrological beliefs with which we find it associated. This belief, Tylor well remarks, arises naturally in the minds of children, and, in accordance with the simplest childlike thought, the cosmologies of the North American Indians and the South Sea Islanders describe their flat earth arched over by the solid vault of heaven. Like thoughts are to be traced on through such details as the Zulu idea that the blue heaven is a rock encircling the earth, inside which are the sun, moon, and stars, and outside which dwell the people of heaven; the modern negro's belief that there is a firmament stretched above like a cloth or web; the Finnish poem which tells how Ilinarinen forged the firmament of finest steel and set in it the moon and stars. The New Zealander, with his notion of a solid firmament, through which the waters can be let down on earth through a crack or hole from the reservoir of rain above, could well explain the passage in Herodotus concerning that place in North Africa where, as the Libyans said, the sky is pierced, as well as the ancient Jewish conception of a firmament of heaven, 'strong as a molten mirror,' with its windows through which the rain pours down in deluge from the reservoirs above, windows which late Rabbinical literature tells us were made by taking out two stars.